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The Athena X-ray Integral Unit (X-IFU) is the high resolution X-ray spectrometer, studied since 2015 for flying in the mid-30s on the Athena space X-ray Observatory, a versatile observatory designed to address the Hot and Energetic Universe science theme, selected in November 2013 by the Survey Science Committee. Based on a large format array of Transition Edge Sensors (TES), it aims to provide spatially resolved X-ray spectroscopy, with a spectral resolution of 2.5 eV (up to 7 keV) over an hexagonal field of view of 5 arc minutes (equivalent diameter). The X-IFU entered its System Requirement Review (SRR) in June 2022, at about the same time when ESA called for an overall X-IFU redesign (including the X-IFU cryostat and the cooling chain), due to an unanticipated cost overrun of Athena. In this paper, after illustrating the breakthrough capabilities of the X-IFU, we describe the instrument as presented at its SRR, browsing through all the subsystems and associated requirements. We then show the instrument budgets, with a particular emphasis on the anticipated budgets of some of its key performance parameters. Finally we briefly discuss on the ongoing key technology demonstration activities, the calibration and the activities foreseen in the X-IFU Instrument Science Center, and touch on communication and outreach activities, the consortium organisation, and finally on the life cycle assessment of X-IFU aiming at minimising the environmental footprint, associated with the development of the instrument. Thanks to the studies conducted so far on X-IFU, it is expected that along the design-to-cost exercise requested by ESA, the X-IFU will maintain flagship capabilities in spatially resolved high resolution X-ray spectroscopy, enabling most of the original X-IFU related scientific objectives of the Athena mission to be retained. (abridged)., Comment: 48 pages, 29 figures, Accepted for publication in Experimental Astronomy with minor editing

Understanding the structure and dynamic process of water at the solid–liquid interface is an extremely important topic in surface science, energy science and catalysis1–3. As model catalysts, atomically flat single-crystal electrodes exhibit well-defined surface and electric field properties, and therefore may be used to elucidate the relationship between structure and electrocatalytic activity at the atomic level4,5. Hence, studying interfacial water behaviour on single-crystal surfaces provides a framework for understanding electrocatalysis6,7. However, interfacial water is notoriously difficult to probe owing to interference from bulk water and the complexity of interfacial environments8. Here, we use electrochemical, in situ Raman spectroscopic and computational techniques to investigate the interfacial water on atomically flat Pd single-crystal surfaces. Direct spectral evidence reveals that interfacial water consists of hydrogen-bonded and hydrated Na+ ion water. At hydrogen evolution reaction (HER) potentials, dynamic changes in the structure of interfacial water were observed from a random distribution to an ordered structure due to bias potential and Na+ ion cooperation. Structurally ordered interfacial water facilitated high-efficiency electron transfer across the interface, resulting in higher HER rates. The electrolytes and electrode surface effects on interfacial water were also probed and found to affect water structure. Therefore, through local cation tuning strategies, we anticipate that these results may be generalized to enable ordered interfacial water to improve electrocatalytic reaction rates. Interfacial water consists of hydrogen-bonded water and Na·H2O, its structure changes at hydrogen evolution reaction (HER) potentials, and when structurally ordered it aids interfacial electron transfer, resulting in higher HER rates.

To evaluate the evidence and produce a summary and recommendations for the most common heart and lung point-of-care ultrasound (PoCUS). We reviewed 10 clinical domains/questions related to common heart and lung applications of PoCUS. Following review of the evidence, a summary and recommendations were produced, including assigning levels of evidence (LoE) and grading of recommendation, assessment, development, and evaluation (GRADE). 38 international experts, the expert review group (ERG), were invited to review the evidence presented for each question. A level of agreement of over 75 % was required to progress to the next section. The ERG then reviewed and indicated their level of agreement of the summary and recommendation for each question (using a 5-point Likert scale), which was approved in the case of a level of agreement of greater than 75 %. A level of agreement was defined as a summary of "strongly agree" and "agree" on the Likert scale responses. One question achieved a strong consensus for an assigned LoE of 3 and a weak GRADE recommendation (question 1), the remaining 9 questions achieved broad agreement with an assigned LoE of 4 and a weak GRADE recommendation (question 2), three achieved an LoE of 3 with a weak GRADE recommendation (questions 3-5), three achieved an LoE of 3 with a strong GRADE recommendation (questions 6-8) and the remaining two were assigned an LoE of 2 with a strong GRADE recommendation (questions 9 and 10). These consensus-derived recommendations should aid clinical practice and highlight areas of further research for PoCUS in acute settings.ZIEL: Bewertung der Evidenz und Erstellung einer Zusammenfassung sowie von Empfehlungen für die häufigsten Herz- und Lungenanwendungen des Point-of-Care-Ultraschalls (PoCUS). Wir überprüften 10 klinische Bereiche bzw. Fragen im Zusammenhang mit den häufigsten Herz- und Lungenanwendungen des PoCUS. Nach der Überprüfung der Evidenz wurden eine Zusammenfassung und Empfehlungen erstellt, einschließlich der Zuordnung von Evidenzgraden (“Level of Evidence” LoE) und der Einstufung der Empfehlung, Bewertung, Entwicklung und Evaluierung (GRADE). Die Expert Review Group (ERG), bestehend aus 38 internationale Experten, wurde aufgefordert, die für jede Fragestellung vorgelegte Evidenz zu überprüfen. Eine Zustimmung von über 75 % war erforderlich, um zum nächsten Teilbereich überzugehen. Anschließend überprüfte die ERG die Ergebnisse und gab den Grad der Zustimmung (mittels 5-stufiger Likert-Skala) bezüglich der Zusammenfassung und Empfehlung für jede Fragestellung an. Diese wurde anerkannt, wenn der Grad der Zustimmung – definiert als Summe der Antworten „stimme voll zu“ und „stimme zu“ auf der Likert-Skala – mehr als 75 % betrug. Bei einer Frage wurde ein starker Konsens bei einem zugeordneten LoE von 3 und einer schwachen GRADE-Empfehlung erzielt (Frage 1). Die übrigen 9 Fragen erzielten eine breite Zustimmung, wobei eine Frage einen LoE von 4 und eine schwache GRADE-Empfehlung erhielt (Frage 2), 3 Fragen erreichten einen LoE von 3 mit schwacher GRADE-Empfehlung (Fragen 3–5), 3 Fragen erreichten einen LoE von 3 mit starker GRADE-Empfehlung (Fragen 6–8) und die verbleibenden 2 Fragen erhielten einen LoE von 2 mit einer starken GRADE-Empfehlung (Fragen 9 und 10). Diese konsensbasierten Empfehlungen sollen die klinische Praxis unterstützen und Bereiche für weitere Forschung hinsichtlich des PoCUS in der Akutversorgung aufzeigen.

To evaluate the evidence and produce a summary and recommendations for the most common heart and lung applications of point-of-care ultrasound (PoCUS). We reviewed 10 clinical domains/questions related to common heart and lung applications of PoCUS. Following review of the evidence, a summary and recommendation were produced, including assignment of levels of evidence (LoE) and grading of the recommendation, assessment, development, and evaluation (GRADE). 38 international experts, the expert review group (ERG), were invited to review the evidence presented for each question. A level of agreement of over 75 % was required to progress to the next section. The ERG then reviewed and indicated their level of agreement regarding the summary and recommendation for each question (using a 5-point Likert scale), which was approved if a level of agreement of greater than 75 % was reached. A level of agreement was defined as a summary of "strongly agree" and "agree" on the Likert scale responses. One question achieved a strong consensus for an assigned LoE of 3 and a weak GRADE recommendation (question 1). The remaining 9 questions achieved broad agreement with one assigned an LoE of 4 and weak GRADE recommendation (question 2), three achieving an LoE of 3 with a weak GRADE recommendation (questions 3-5), three achieved an LoE of 3 with a strong GRADE recommendation (questions 6-8), and the remaining two were assigned an LoE of 2 with a strong GRADE recommendation (questions 9 and 10). These consensus-derived recommendations should aid clinical practice and highlight areas of further research for PoCUS in acute settings.ZIEL: Bewertung der Evidenz und Erstellung einer Zusammenfassung sowie von Empfehlungen für die häufigsten Herz- und Lungenanwendungen des Point-of-Care-Ultraschalls (PoCUS). Wir überprüften 10 klinische Bereiche bzw. Fragen im Zusammenhang mit den häufigsten Herz- und Lungenanwendungen des PoCUS. Nach der Überprüfung der Evidenz wurden eine Zusammenfassung und eine Empfehlung erstellt, einschließlich der Zuordnung von Evidenzgraden („Level of Evidence“ LoE) und der Einstufung der Empfehlung, Bewertung, Entwicklung und Evaluierung (GRADE). Die Expert Review Group (ERG), bestehend aus 38 internationalen Experten, wurde aufgefordert, die für jede Fragestellung vorgelegte Evidenz zu überprüfen. Eine Zustimmung von über 75 % war erforderlich, um zum nächsten Teilbereich überzugehen. Anschließend überprüfte die ERG die Ergebnisse und gab den Grad der Zustimmung (mittels 5-stufiger Likert-Skala) bezüglich der Zusammenfassung und Empfehlung für jede Fragestellung an. Diese wurde anerkannt, wenn der Grad der Zustimmung – definiert als Summe der Antworten „stimme voll zu“ und „stimme zu“ auf der Likert-Skala – mehr als 75 % betrug. Bei einer Frage wurde ein starker Konsens bei einem zugeordneten LoE von 3 und einer schwachen GRADE-Empfehlung erzielt (Frage 1). Die übrigen 9 Fragen erzielten eine breite Zustimmung, wobei eine Frage einen LoE von 4 und eine schwache GRADE-Empfehlung erhielt (Frage 2), 3 Fragen erreichten einen LoE von 3 mit schwacher GRADE-Empfehlung (Fragen 3–5), 3 Fragen erreichten einen LoE von 3 mit starker GRADE-Empfehlung (Fragen 6–8) und die verbleibenden 2 Fragen erhielten einen LoE von 2 mit einer starken GRADE-Empfehlung (Fragen 9 und 10). Diese konsensbasierten Empfehlungen sollen die klinische Praxis unterstützen und Bereiche für weitere Forschung im Bereich des PoCUS in der Akutversorgung aufzeigen.

Introduction Bile acid diarrhoea (BAD) can occur due to disruption to the enterohepatic circulation, e.g. following cholecystectomy. Post-cholecystectomy diarrhoea has been reported in 2.1–57.2% of patients; however, this is not necessarily due to BAD. The aim of this study was to determine the rates of bile acid diarrhoea diagnosis after cholecystectomy and to consider investigation practices. Methods A retrospective analysis of electronic databases from five large centres detailing patients who underwent laparoscopic cholecystectomy between 2013 and 2017 was cross-referenced with a list of patients who underwent 75SeHCAT testing. A 7-day retention time of p Results A total of 9439 patients underwent a laparoscopic cholecystectomy between 1 January 2013 and 31 December 2017 in the five centres. In total, 202 patients (2.1%) underwent investigation for diarrhoea via 75SeHCAT, of which 64 patients (31.6%) had a 75SeHCAT test result of >15%, while 62.8% of those investigated were diagnosed with bile acid diarrhoea (BAD). In total, 133 (65.8%) patients also underwent endoscopy and 74 (36.6%) patients had a CT scan. Median time from surgery to 75SeHCAT test was 672 days (SD ± 482 days). Discussion/Conclusion Only a small proportion of patients, post-cholecystectomy, were investigated for diarrhoea with significant time delay to diagnosis. The true prevalence of BAD after cholecystectomy may be much higher, and clinicians need to have an increased awareness of this condition due to its amenability to treatment. 75SeHCAT is a useful tool for diagnosis of bile acid diarrhoea.

Sodium–oxygen battery cathodes utilise the reversible redox species of oxygen in the presence of sodium ions. However, the oxygen reduction and evolution reaction mechanism is yet to be conclusively determined. In order to examine the part played by surface structure in sodium–oxygen electrochemistry for the development of catalytic materials and structures, a method of preparing clean, well-defined Pt electrode surfaces for adsorption studies in aprotic solvents is described. Using cyclic voltammetry (CV) and in situ electrochemical shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS), the various stages of oxygen reduction as a function of potential have been determined. It is found that on Pt{111} and Pt{110}-(1 × 1) terraces, a long lived surface sodium peroxide species is formed reversibly, whereas on Pt{100} and polycrystalline electrodes, this species is not detected.

BackgroundFollowing blunt trauma, diagnosis of shoulder dislocation based on physical examination alone is difficult due to possible concurrent proximal humeral fractures. X-rays are therefore used to confirm diagnosis. Results from recent observational studies comparing diagnostic accuracy of point-of-care ultrasound (PoCUS) with X-rays for shoulder dislocation have been encouraging. The aim of this study was to determine whether PoCUS improves diagnostic accuracy when used with physical examination for the diagnosis of shoulder dislocation, proximal humeral fracture and ascertaining successful reduction in the ED.MethodsA prospective, single-centre, open, parallel randomised control study over a 6-month period was used to answer the research question and test the null hypothesis. Consecutive eligible adult patients attending the ED of Mater Dei Hospital in Malta were randomised to either the control (C) (physical examination only) or experimental group (E) (physical examination and a two-point PoCUS scan). The study objectives were to measure diagnostic accuracy for both examinations for detecting shoulder dislocation, any associated proximal humeral fractures and confirming reduction. X-rays were used as reference standard for both groups.Results1206 patients were enrolled in this study (C n=600, E n=606). 290 dislocations (C n=132 and E n=158), 332 proximal humeral fractures (C n=154 and E n=178) and 278 reductions (C n=130 and E n=148) were analysed. A statistically significant difference (pConclusionsThe addition of PoCUS to a physical examination significantly improves diagnostic accuracy for dislocations, proximal humeral fractures and reduction confirmation.Trial registration numberInternational Standard Randomised Controlled Trials Number Registry (ISRCTN17048126).

Cyclic voltammetry has been used to probe the initial stages of oxygen reduction and oxidation in lithium-containing dimethyl sulfoxide at well-defined Pt single crystal electrodes in order to elucidate any catalytic effects ascribable to surface structure. In contrast to previous work involving sodium-oxygen, lithium-oxygen studies did not yield any significant differences for reaction on the three basal planes of platinum. Rather, all three planes generated a similar voltammetric response. However, by judicious use of various potential sweep limits, the formation of superoxide together with both a “conformal” or surface adlayer of lithium peroxide (Li2O2) together with a “microcrystallite” surface Li2O2 phase was resolved. Voltammetric peak intensity versus sweep rate measurements confirmed that superoxide electrooxidation was diffusion limited whereas electrooxidation of the two Li2O2 phases displayed behaviour typical of a surface-confined process. Under steady-state conditions for the formation of superoxide, it was found that for both the conformal and microcrystallite Li2O2 phases, electrooxidation followed zero-order kinetics, pointing to the importance of free surface sites in facilitating these reactions. A marked change in the rate of Li2O2 formation was found to coincide with a coverage of 0.25 monolayers, as measured by the charge density of the conformal Li2O2 electrooxidation peak. We postulate that electron tunnelling through both the conformal Li2O2 layer and microcrystallites deposited on this surface layer coincides with this coverage and accounts for such behaviour. This phenomenon of electron tunnelling through single conformal and mixed conformal/microcrystallite structures should prove vitally important in governing the overall electrooxidation rate.

ObjectivesCholecystectomy is one of the most common surgical procedures performed worldwide to treat gallstone-related disease. Postcholecystectomy diarrhoea (PCD) is a well-reported phenomenon, however, the actual rate, predictive factors and mechanism of action have not been well determined. A systematic review was undertaken to determine the rate and predictive factors associated with diarrhoea in the postcholecystectomy setting.MethodsThe review was conducted according to the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocol. Databases searched included Medline, Embase, Pubmed, Cochrane and Google Scholar up to 29 September 2020. The inclusion criteria consisted of cohort studies or randomised trials which investigated the rate of PCD and predictive factors. Case reports, case series, conference abstracts and expert opinion pieces were excluded as were other systematic reviews as all the original articles from those reviews were included in this review. Papers that did not include PCD as a separate entity were excluded. Bias assessment was performed using the Newcastle-Ottawa Scale for cohort studies and the Cochrane risk of bias tool for randomised controlled trials as appropriate. Data were extracted by two authors (AF and JAA) and an overall rate of PCD was calculated. Predictive factors were also extracted and compared between studies.Results1204 papers were obtained and 21 were found to contain relevant information about PCD, including the number of patients developing diarrhoea, method of symptom assessment and time of onset postcholecystectomy. A pooled total of 3476 patients were included across the identified studies with 462 (13.3%) patients developing PCD. Possible predictive factors varied across all studies, with characteristics such as gender, age and weight of patients postulated as being predictive of PCD, with no agreement across studies.DiscussionPCD is therefore relatively common (13.3%). This has important implications for patient consent. Patients ought to be investigated early for bile acid diarrhoea in suspected PCD. More studies are required to determine the possible predictive factors for PCD. Limitations of the study included that most studies were not powered for calculation of PCD, and assessment methods between studies varied.PROSPERO registration numberCRD42019140444.

By combining cyclic voltammetry (CV) and shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS), the adsorption behavior of two alkynes, propargyl alcohol (PA) and 2-methyl-3-butyn-2-ol (MeByOH), undergoing hydrogenation on Pt basal plane single-crystal electrodes is investigated. It is found that PA and MeByOH give rise to strong surface sensitivities in relation to both hydrogenation activity and molecular fragmentation into adsorbed species such as CO. For PA, irreversible adsorption is strongly favored for Pt{100} and Pt{110} but is weak in the case of Pt{111}. It is suggested that the presence of the primary alcohol substituent is key to this behavior, with the order of surface reactivity being Pt{100} > Pt{110} > Pt{111}. In contrast, for MeByOH, strong irreversible adsorption is observed on all three basal plane Pt surfaces and we propose that this reflects the enhanced activity of the alkyne moiety arising from the inductive effect of the two methyl groups, coupled with the decreased activity of the tertiary alcohol substituent toward fragmentation. Pt{111} also exhibits singular behavior in relation to MeByOH hydrogenation in that a sharp Raman band at 1590 cm–1 is observed corresponding to the formation of a di-σ/π-bonded surface complex as the alkyne adsorbs. This band frequency is some 20 cm–1 higher than the analogous broadband observed for PA and MeByOH adsorbed on all other basal plane Pt surfaces and may be viewed as a fingerprint of Pt{111} terraces being present at a catalyst surface undergoing hydrogenation. Insights into the hydrogenation activity of different Pt{hkl} surfaces are obtained using quantitative comparisons between Raman bands at hydrogenation potentials and at 0.4 V vs Pd/H, the beginning of the double-layer potential region, and it is asserted (with support from CV) that Pt{110} is the most active plane for hydrogenation due to the presence of surface defects generated via the lifting of the (1 × 2) to (1 × 1) clean surface reconstruction following flame annealing and hydrogen cooling. Our findings are also consistent with the hypothesis that Pt{111} planes are most likely to provide semihydrogenation selectivity of alkynes to alkenes, as reported previously.

The adsorption and electrooxidation of CO molecules at well-defined Pt(hkl) single-crystal electrode surfaces is a key step towards addressing catalyst poisoning mechanisms in fuel cells. Herein, we employed in situ electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) coupled with theoretical calculation to investigate CO electrooxidation on Pt(hkl) surfaces in acidic solution. We obtained the Raman signal of top- and bridge-site adsorbed CO* molecules on Pt(111) and Pt(100). In contrast, on Pt(110) surfaces only top-site adsorbed CO* was detected during the entire electrooxidation process. Direct spectroscopic evidence for OH* and COOH* species forming on Pt(100) and Pt(111) surfaces was afforded and confirmed subsequently via isotope substitution experiments and DFT calculations. In summary, the formation and adsorption of OH* and COOH* species plays a vital role in expediting the electrooxidation process, which relates with the pre-oxidation peak of CO electrooxidation. This work deepens knowledge of the CO electrooxidation process and provides new perspectives for the design of anti-poisoning and highly effective catalysts.

A phenomenological theory of electrosorption is presented based upon notions of local charge and local electronic polarisability (Friedel oscillations). The strong link between the extent and nature of ionic and molecular adsorption at an electrode surface and the uv-absorption properties displayed by such molecular entities in an aqueous solution is emphasised. The theory may be used to predict, in certain cases the extent of ionic adsorption at the potential of zero charge (PZC) and, also, to rationalise recent results pertaining to metal underpotential deposition (UPD) processes on single crystal electrodes.

We discuss the possibility of a new mechanism for the hydrogen evolution reaction (HER) involving hydrogen anion as the reaction intermediate. A simple thermodynamic analysis reveals that this mechanism is unfavourable at most relevant catalysts in aqueous solution in the usual potential range encountered for the HER. Its likelihood, however, increases when the dielectric permittivity of the electrolyte solution decreases, the work function of the catalyst decreases, and when the electrode potential decreases. We suggest that carbon-based catalysts with low dielectric constant solvents, such as n-Hexane, are plausible systems to observe hydrogen anion as the intermediate for hydrogen reactions. In the cases where the proposed HER mechanism is permissible, values of Tafel slope are calculated using a simple kinetic analysis based on the rate-determining term concept.

Hydrogen oxidation and oxygen reduction are two crucial energy conversion reactions, which are shown to be both strongly affected by the presence of intrinsically microporous polymer coatings on electrodes. Polymers of intrinsic microporosity (PIMs) are known to possess extremely high internal surface area and ability to bind gases under dry conditions. It is shown here that both, hydrogen- and oxygen gas binding into PIMs, also occurs under wet or “triphasic” conditions in aqueous electrolyte environments (when immersed in 0.01 M phosphate buffer at pH 7). For two known PIM materials (PIM-1 and PIM-PY), nanoparticles are formed by an anti-solvent precipitation protocol and then cast as a film onto platinum or glassy carbon electrodes. Voltammetry experiments reveal evidence for hydrogen and oxygen binding. Both, PIM-1 and PIM-PY, locally store hydrogen or oxygen gas at the electrode surface and thereby significantly affect electrocatalytic reactivity. The onset of oxygen reduction on glassy carbon is shifted by 0.15 V in the positive direction.

The electrochemical reduction of nitrate anions in aqueous 0.1 M perchloric acid has been studied using Pt(S)-[n{1 1 0} × {1 1 1}] and Pt(S)-[n{1 1 0} × {1 0 0}] single crystal electrodes. It is demonstrated that the presence of Pt{1 1 0} adsorption sites is associated with a single, broad nitrate reduction peak centred at 0.18 V (RHE). Moreover, depending on the cooling environment used after flame-annealing (CO, H2, Ar, air, nitrogen), the surface concentration of such sites varies which in turn regulates the nitrate reduction current density achievable for a given stepped Pt{h k l} electrode. The origin of this phenomenon is the propensity of the clean Pt{1 1 0} basal plane (and vicinal surfaces containing this plane) to reconstruct towards a stable (1 × 2) phase with strong CO chemisorption favouring formation of larger Pt{1 1 0}-(1 × 1) domains. In contrast, argon/air-cooling appears to promote the development of a largely (1 × 2) reconstructed surface which is much less active for nitrate reduction since the surface density of Pt{1 1 0}-(1 × 1) terrace sites is significantly diminished. Interestingly, hydrogen-cooling affords nitrate reduction activity intermediate between these two extremes. We suggest that under this particular preparation condition, a partially deconstructed (1 × 1) phase forms containing the “excess” 50% of surface atoms (originating from the (1 × 2) phase) sitting proud of the surface in the form of small (1 × 1) islands, together with residual (1 × 2) missing row regions. Hence, after hydrogen cooling, the nominal Pt{1 1 0} surface plane is speculated to exhibit a wider distribution of smaller terrace widths than found with CO cooling together with residual areas of (1 × 2). The weaker chemisorption of hydrogen apparently limits the size of the Pt{1 1 0}-(1 × 1) domains achievable and consequently, nitrate reduction activity is diminished. Based on these findings, it is proposed that nitrate reduction may be used as a quantitative electrochemical probe of Pt{1 1 0}-(1 × 1) sites at Pt nanoparticles in an analogous fashion to the method of ammonia electrooxidation presently used to quantify the surface abundance of Pt{1 0 0} sites. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001. JMF wishes to thank MINECO for support from project CTQ2016-76221-P (AEI/FEDER, UE).

Surface activation and cleaning of platinum micro-wires of 25 micron diameter has been achieved by a short one-second electrothermal annealing treatment in air at 0.3 A (to orange glow). Voltammetric data suggest a decrease in the electrochemically active surface area with annealing time and a change in surface structure towards the Pt(100) crystalline face. The impact of electrothermal annealing on the electrocatalytic activity towards (i) oxygen reduction and (ii) glucose oxidation in pH 7 phosphate buffered aqueous solutions is investigated. In contrast to as-received platinum, annealed platinum produces an electrocatalytic response towards glucose oxidation with increasing glucose concentration. A short one-second anneal step is just as effective in enhancing catalysis as prolonged electrochemical cleaning in sulphuric acid. Finally, by combining a non-annealed and an annealed microwire electrode, a very simple membrane-free micro-fuel cell system is devised operating in phosphate buffer at pH 7 with linearly increasing power output reaching 2.2 nW cm−2 for high glucose levels of 0.5 M.

Stainless-steel rods were manufactured by laser additive manufacturing (LAM or "3D-printing") from a stainless-steel (316L) powder precursor, and then investigated and compared to conventional stainless steel in electrochemical experiments. The LAM method used in this study was based on "powder bed fusion", in which particles with an average diameter of 20-40μm are fused to give stainless-steel rods of 3mm diameter. In contrast to conventional bulk stainless-steel (316L) electrodes, for 3D-printed electrodes, small crevices in the surface provide residual porosity. Voltammetric features observed for the 3D-printed electrodes immersed in aqueous phosphate buffer are consistent with those for conventional bulk stainless steel (316L). Two chemically reversible surface processes were observed and tentatively attributed to Fe(II/III) phosphate and Cr(II/III) phosphate. Galvanic exchange is shown to allow improved platinum growth/adhesion onto the slightly porous 3D-printed stainless-steel surface, resulting in a mechanically robust and highly active porous platinum deposit with good catalytic activity toward methanol oxidation.

The in situ combination of electrochemistry and shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS) has been used for the first time to investigate the surface structure sensitivity of asymmetric catalytic hydrogenation at single-crystal Pt electrodes. The adsorption and hydrogenation behavior of aqueous ethyl pyruvate (EP) at a range of modified and unmodified Pt{hkl} electrodes was measured both by cyclic voltammetry and by recording Raman spectra at hydrogen evolution potentials. Two primary surface intermediates were observed, including the previously reported half-hydrogenation state (HHS), formed by addition of a hydrogen atom to the keto carbonyl group, as well as a new species identified as intact chemisorbed EP bound in a μ2(C,O) configuration. The relative populations of these two species were sensitive to the Pt surface structure; whereas the μ2(C,O) EP adsorbate was dominant at pristine Pt{111} and Pt{100}, the HHS was only observed at these electrodes after the introduction of d...

Attenuated total reflection infrared (ATR-IR) spectroscopy has been combined with electrochemical methods to investigate molecular decomposition and self-poisoning processes on platinum surfaces under the conditions of catalytic hydrogenation. In aqueous 0.1 M H2SO4 the α-keto ester ethyl pyruvate (EP) is found to decompose on polycrystalline platinum electrodes to yield surface-adsorbed CO, but the observed behavior is highly dependent on the electrode potential, a parameter intimately linked to the surface-adsorbed hydrogen coverage. In the potential range −0.2 to −0.4 V (vs mercury/mercurous sulfate electrode) where the hydrogen coverage is negligible, CO is readily produced at the platinum surface along with other molecular fragments but the decomposition process becomes inhibited at high EP solution concentrations. At −0.5 V only very low coverages of CO are observed due to competing hydrogen adsorption at Pt(100) step sites which most favor EP decomposition. At more negative potentials, during the o...

The structure and molecular processes occurring at the Nafion® membrane/electrode interface remain poorly understood. The present study aims at elucidating the nano-scale properties of the Pt(100)/Nafion® interface using scanning probe techniques, namely STM and AFM. In STM, the surface morphology of the thin Nafion® film appears smooth on the atomic scale; monoatomic steps of the substrate are well visible. The thickness of the Nafion® membrane is determined using AFM tip penetration experiments and also by scratching of the Nafion® layer from the electrode surface. Force deflection (“approach”) curves demonstrate that the tip penetrates the Nafion® layer at a normal force greater than 5 nN.

By flame-annealing and cooling a series of Pt n{110} × {111} and Pt n{110} × {100} single crystal electrodes in a CO ambient, new insights into the nature of the electrosorption processes associated with Pt{110} voltammetry in aqueous acidic media are elucidated. For Pt n{110} × {111} electrodes, a systematic change in the intensities of so-called hydrogen underpotential (Hupd) and oxide adsorption voltammetric peaks (for two dimensionally ordered (1 × 1) terraces and linear {111} × {111}step sites) point to a lack of surface reconstruction with all surfaces adopting a (1 × 1) configuration. This is in contrast to hydrogen cooled analogues which give rise to significant residual surface disorder, probably associated with the excess 50% of atoms remaining atop of the surface upon deconstruction of the {110} − (1 × 2) terrace phase. In contrast, Pt n{110} × {100} stepped electrodes, when cooled in gaseous CO following flame-annealing, show a marked tendency towards surface reconstruction, even at low step densities. Variations in potential of the Pt{110}-(1 × 1) Hupd electrosorption peaks as a function of specific ion adsorption strength and pH point to weak specific adsorption for both anions (including perchlorate and fluoride) and cations (including Na+ and K+). CO charge-displacement measurements of the potential of zero total charge (PZTC) allow inferences to be made concerning the nature of the electrosorbed species in the hydrogen underpotential deposition (Hupd) region. Hence, a coherent interpretation of the complex voltammetric phenomena often displayed by platinum surfaces vicinal to the {110} plane is proposed. GAA acknowledges the financial support of the EPSRC towards a studentship for KH. RMH thankfully acknowledges support from Generalitat Valenciana under the Santiago Grisolia Program (GRISOLIA/2013/008). Partial support from MINECO (Spain) Project CTQ 2013-44083-P is greatly acknowledged.

A water-insoluble Polymer with Intrinsic Microporosity (or PIM, here for the particular case of the Tröger Base system PIM-EA-TB, BET area ca. 103 m2 g−1) is demonstrated to act as a rigid host environment for highly water-insoluble molecular catalysts, here tetraphenylporphyrinato-iron (FeTPP), surrounded by aqueous solution-filled micropores. A PIM-EA-TB film containing catalyst is deposited onto the electrode and immersed for voltammetry (i) with 4-(3-phenyl-propyl)-pyridine to give an organogel, or (ii) bare directly into aqueous solution. The porous host allows processes to be optimised as a function of solution phase, composition, and catalyst loading. Effective electron transfer as well as effective electrocatalysis is reported for aqueous oxygen and peroxide reduction. Given the use of completely water-insoluble catalyst systems, the methodology offers potential for application with a wide range of hitherto unexplored molecular electrocatalysts and catalyst combinations in aqueous media. Keywords: Electrocatalysis, Ion transfer, Peroxide, Oxygen, Fuel cell, Sensing

PtM overlayers (where M=Fe, Co or Ni) supported on Pt{111} are prepared via thermal annealing in either a nitrogen/water or hydrogen ambient of dilute aqueous droplets containing M(Z+) cations directly attached to the electrode. Two different PtM phases are detected depending on the nature of the post-annealing cooling environment. The first of these consists of small (20 nm), closely packed microcrystals comprised of a central metallic core and a shell (several monolayers thick) of mixed metal oxides/hydroxides. The second type of PtM phase is prepared by cooling in a stream of hydrogen gas. Although this second phase also consists of numerous microcrystals covering the Pt{111} electrode surface, these are both flatter than before and moreover are entirely metallic in character. A positive shift in the onset of PtM oxide formation correlates with increased activity towards the oxygen reduction reaction (ORR), which we ascribe to the greater availability of platinum metallic sites under ORR conditions.

The enzymeless glucose oxidation process readily occurs on nano-gold electrocatalyst at pH7, but it is highly susceptible to poisoning (competitive binding), for example from protein or chloride. Is it shown here that gold nanoparticle catalyst can be protected against poisoning by a polymer of intrinsic microporosity (PIM-EA-TB with BET surface area 1027m2g-1). This PIM material when protonated, achieves a triple catalyst protection effect by (i) size selective repulsion of larger protein molecules (albumins) and (ii) membrane ion selection effects, and (iii) membrane ion activity effects. PIM materials allow "environmental control" to be introduced in electrocatalytic processes.

The electrooxidation of formic acid and methanol on Pt{1 1 1} in aqueous sulphuric and perchloric acid as a function of both palladium coverage and Nafion adsorption is reported. Nafion is a proton conducting polymer commonly used as a membrane electrolyte in fuel cells. Understanding the interaction of Nafion with platinum and other bimetallic electrocatalytic surfaces is therefore of crucial importance if one is to optimise fuel cell performance. Here, we demonstrate that for formic acid electrooxidation, Nafion behaves as a weakly adsorbing electrolyte exhibiting similar properties to aqueous perchloric acid. Adsorbed palladium is observed to promote formic acid electrooxidation on Pt{1 1 1} and a maximum in electrooxidation rate is found when a single monolayer of palladium on Pt{1 1 1} is formed in agreement with previous studies. In contrast, aqueous sulphuric acid strongly inhibits formic acid electrooxidation due to extensive specific adsorption of (bi-)sulphate anions on the palladium adlayer which compete successfully with molecules of formic acid for adsorption sites. In all electrolytes studied, unique electrooxidation peaks ascribable to formic acid electrooxidation occurring on first and second/third layer palladium islands are observed. We ascribe this behaviour to a strong coupling of formic acid adsorption with changes in the local potential of zero total charge as a function of palladium coverage. Hence, it is deduced that Pd/Pt electrocatalysts utilising Nafion membranes should not prove deleterious to electrocatalytic activity. In contrast, similar measurements but using methanol instead of formic acid indicated that methanol electrooxidation is inhibited significantly when Nafion is adsorbed relative to activity recorded in aqueous perchloric acid. In addition, palladium adlayers on Pt{1 1 1} are found to inhibit methanol electrooxidation in all electrolytes studied, presumably because the key Csingle bondH methanol dissociation step is less favoured on palladium compared to platinum. It is concluded that the role of specifically adsorbed anions is crucial in order to afford optimal fuel cell performance and that for methanol at least, proton conducting membranes other than Nafion should be considered although for formic acid, Nafion appears to be ideal.

The adsorption of citrate anions on Pt{h k l} single crystal electrodes and Pt nanoparticles was investigated using cyclic voltammetry (CV). Citrate is found to behave as a simple, specifically adsorbing anion, stronger in its surface interaction with platinum than either (bi-) sulphate or OH but displaying no tendency to decompose at 293 K into molecular fragments such as chemisorbed carbon monoxide. No preference for a particular adsorption site was exhibited by citrate either, as would be expected from its reported ability to control the shape of growing Pt nanoparticles. Rather, citrate is readily removed from platinum surfaces either by exposure to aqueous sodium hydroxide (it acts as a non-specifically adsorbing anion at high pH) or potential excursions to potentials

"Bamboo-like" multiwalled (b-MWCNT), "hollow-tube" multiwalled (h-MWCNT) and single-walled carbon nanotubes (SWCNT), chemically modified with 1-anthraquinonyl (AQ) or 4-nitrophenyl (NP) groups, are characterized using voltammetric, electron microscopic and Raman spectroscopic techniques. The pKa values of the AQ-modified CNTs are found to be shifted by greater than three units when compared to the pKa values of anthrahydroquinone (AHQ, the reduced form of AQ) in aqueous solution to beyond pH 14. These large changes in the surface pKa values of the modified CNTs are explored further by comparing the pKa values of CNTs modified with an anthraquinonyl-2-carboxylic acid group. These groups are attached to the CNT surface via the formation of an amide bond with an aminophenyl "spacer" unit derived from the chemical reduction of NP modified CNTs. The location of reactive sites on the CNT surface is investigated and their influence on the pKa of the modified materials is discussed. Comparison with modified pyrolytic graphite electrodes exposing pure edge-plane or pure basal-plane crystal faces indicates that the modifying aryl groups are predominantly located on edge-plane like defects at the tube ends of MWCNTs. The effect of polymer formation on electron transfer kinetics of b-MWCNTs and h-MWCNTs is also discussed. In contrast SWCNTs show both significant side-wall functionalisation and fast electron transfer kinetics which is attributed to their different electronic structure. This journal is © The Royal Society of Chemistry.

The biomanufacture of two types of platinum bionanoparticle (bioNP) using Escherichia coli MC4100(1% and 20% by mass metal loading) together with a method for both liberating the nanoparticles (NPs) from the bacterial layer and their subsequent critical cleaning is reported. The possibility of an enantiomeric excess of chiral kink sites forming on the surface of the Pt nanoparticles produced by the bacteria was investigated using the electrooxidation of D- and L-glucose as the chiral probe. Transmission electron microscopy revealed that the Pt bioNPs (after recovery and cleaning) were typically 2.3 ± 0.7 nm (1% loading) and 4.5 ± 0.7 nm (20% loading) in diameter. The D- and L-glucose electrooxidation measurements did not give rise to any chiral response using either of the Pt bioNPs types but did display differing CV profiles. This suggested that the overall surface morphology of each bioNP could be controlled by the degree of metal loading but that no enantiomeric excess of intrinsically chiral surface kink sites was present.

The selectivity towards 1,4-butynediol hydrogenation of both a standard 5 wt % Pt on graphite supported catalyst and a biogenic Pt analogue is reported. In both cases, it is determined using cyclic voltammetry that step sites afford the greatest extent of hydrogenation and that deliberate blocking of such sites gives rise to significant selectivity in favor of the 1,4-butenediol product. For the 5 wt % Pt/graphite catalyst, irreversible adsorption of bismuth was used as the step site blocking agent. In the case of the biogenic Pt nanoparticles (NPs) synthesized within the bacterium Escherichia coli, residual molecular organic fragments, left over after chemical cleaning and subsequent separation from the bacterial support, were observed to have accumulated preferentially at defect sites. This phenomenon facilitated an increase in selectivity toward alkenic products of up to 1.4 during hydrogenation of the alkyne. When biogenic NPs of platinum supported upon bacterial biomass were also investigated, they too were found to be active and selective although selectivity toward 1,4-butenediol was optimized only after the particles were chemically cleaned and separated from the biomass. Bi-poisoned 5% Pt on graphite, although highly selective, gave half the reaction rate of the biogenic counterpart (20% and 45% conversion of starting material respectively after 2 h), but the latter exhibited less selectivity for butenediol (0.7 and 0.9 respectively). It is proposed therefore that such biogenic materials may potentially act in a similar manner to Lindlar-type catalysts, used extensively in organic synthesis for selective hydrogenation of alkynes, in which an additive partially poisons metal sites but without the associated hazards of toxic heavy metals such as lead being present.

The electrooxidation of d- and l-glucose at chiral Pt{321}r/s single crystal electrodes modified with Au, Ag and Bi adatoms up to a coverage of one monolayer (ML) is reported. All adatoms investigated are found to selectively decorate kink and step sites. Only at higher coverages is adsorption onto the narrow {111} terrace sites observed for Bi, Ag and Au, consistent with previously reported adsorption behaviour on stepped surfaces vicinal to the {111} plane for chemisorbates exhibiting a lower work function than platinum. However, silver is found to block {111} terrace sites even when Pt step sites are still available on Pt{321}. This behaviour is ascribed to the propensity of silver to undergo place-exchange to form a surface alloy. The selective decoration of chiral kink sites has a profound influence on the voltammetric response of Pt{321} towards glucose electrooxidation. For bismuth adsorption, the electrooxidation current density initially increases and reaches a maximum when bismuth adsorption at {111} terraces commences. This is because the reaction pathways at step/kink sites leading to the formation of adsorbed CO (a surface poison for the clean surface reaction) and other strongly adsorbed intermediates, are either blocked by adsorbed bismuth or their electrooxidation and subsequent removal promoted. Once all step/kink sites are blocked by bismuth, hardly any chiral discrimination can be discerned between r-/s-electrodes towards d-/l-glucose. Silver adsorption does not cause any increase in glucose electrooxidation current density but rather induces a continual attenuation in glucose electrooxidation activity, particular (in contrast to bismuth) electrooxidation current at potentials in excess of 0.35 V. Therefore, unlike for bismuth, the initial glucose adsorption and electrooxidation processes associated with chiral kink sites appear to be preserved even though silver adsorbs at these sites. It is speculated that spontaneous place-exchange of silver with platinum to form a PtAg surface alloy at steps is responsible for this difference in behaviour between silver and bismuth. Finally, gold neither promotes reaction rate nor preserves chiral discrimination and is therefore deduced to act as an inert site blocker (no alloying, no promotion of CO electrooxidation) leading to complete attenuation of glucose electrooxidation current at a coverage of one ML.

Adsorption of ethyl pyruvate (EP) and methyl pyruvate (MP) has been studied on a SERS-active platinum electrode. Gas-phase experiments under a hydrogen atmosphere show that decarbonylation to form adsorbed CO together with formation of a half-hydrogenated state of MP/EP are the dominant surface reaction pathways occurring under these conditions. Similar findings were obtained using a hydrogen-evolving platinum electrode under potentiostatic control in 0.1 M aqueous sulfuric acid containing EP or MP. DFT calculations have been used to support the assignment of vibrational bands in the SERS obtained from the half-hydrogenated state intermediate. At hydrogen evolution potentials and using concentrations of MP and EP < 0.02M, adsorbed hydrogen adatoms were detected. At higher EP concentrations, hydrogen-atom formation was inhibited by the greater surface coverages of the half-hydrogenated state of EP/MP and to a lesser extent adsorbed CO derived from decarbonylation side reactions. Addition of the chiral modifier cinchonidine (CD) to the acidic electrolyte under conditions of hydrogen evolution resulted in significantly less CO production and a reduction in the intensity of all SERS peaks associated with the half-hydrogenated state. Most importantly, however, the presence of surface hydrogen, previously absent on the unmodified surface, was always observed irrespective of the EP concentration. The significance of this result in relation to the question of the origin of rate enhancement during heterogeneously catalyzed enantioselective hydrogenation of α-ketoesters is discussed.

Ultrathin Nafion overlayers ranging from 0 to 3.3 nm in thickness have been deposited on platinum single crystal electrodes in order to study their voltammetric behavior as a function of both Nafion surface coverage and platinum surface step density. Unusual structural sensitivity of Nafion-induced voltammetric peaks ascribable to Nafion interactions with step sites is observed as a function of average terrace width. For stepped surfaces containing both {111} and {100} terraces, average terrace widths of 2–3 atoms give rise to the most intense Nafion-step electrosorption peaks. Rapid quenching of the Nafion-step voltammetric peaks is observed as the average terrace width is gradually increased until for >5 atom wide terraces all such electrochemical features are completely attenuated. This rapid diminution of the step-Nafion voltammetric peak, within just three atoms of terrace width, is unprecedented, and a parallel with the “splitting” of hydrogen underpotential deposition (HUPD) step peaks in perchloric acid aqueous electrolyte for closely spaced steps is noted. On the basis of these measurements, it is suggested that Nafion is a molecular probe of adsorbed OH species on Pt electrodes.

The electrooxidation of adsorbed and bulk solution of 10−2 M ethanol and D6-ethanol at polycrystalline platinum, smooth, roughened and Ru modified Pt(3 3 2), Pt(3 3 1) and Pt(1 1 1) electrodes was studied by on-line differential electrochemical mass spectroscopy (DEMS) using a dual thin layer flow through cell. On polycrystalline Pt, the main (or even single) product is acetaldehyde; due to the flow through conditions the amount of acetaldehyde further oxidized to acetic acid is negligible. At stepped single crystals with (1 1 1) terraces (Pt(s)[n(1 1 1) × (1 1 1)], acetic acid is produced at a lower potential than acetaldehyde. This demonstrates that in addition to the reaction path involving C–C bond splitting leading to CO2 (via adsorbed CO and CHx) and the reaction path leading to acetaldehyde there is a third, direct reaction path leading to the formation of acetic acid. Step decoration by Ru does not lead to an increased reactivity. This is different from the strong cocatalytic effect of Ru at step sites on the oxidation of CO. Furthermore, Ru does not influence the relative amount of acetaldehyde formed.

Ru quasi-single-crystal electrodes, prepared by resistive heating of Ru deposited on Pt single-crystal surfaces in a nitrogen atmosphere, have been used to study copper underpotential deposition (Cu-UPD), Bulk and surface Cu stripping experiments were performed on the low-index Ru/Pt(1 0 0), Ru/Pt(1 1 0) and Ru/Pt(1 1 1) quasi-crystalline film electrodes and also stepped Ru/Pt(S)[n(1 0 0) × (1 1 1)] and Ru/Pt(S)[4(1 1 1) × (1 0 0)] electrodes vicinal to the (1 0 0) and (1 1 1) planes respectively. Upon performing Cu-UPD experiments in the potential range from 0 to 500 mV vs. Cu/Cu2+ on the Ru/Pt(1 0 0) quasi-single-crystal film electrode, a single peak for Cu-UPD was observed at a potential of about 200 mV vs. Cu/Cu2+. Its charge density was close to that for copper on the clean Pt(1 0 0) single-crystal substrate consistent with a coverage of one monolayer (1.3 × 1015 atoms cm−2). In contrast, on Ru/Pt(1 1 0) and Ru/Pt(1 1 1), no significant amounts of Cu could be deposited – possibly due to competitive adsorption by adsorbed oxygen-species. For Cu-UPD on stepped Ru/Pt(S)[n(1 0 0) × (1 1 1)] film electrodes vicinal to the (1 0 0) plane, a peak was also found in the same potential range as observed for Ru/Pt(1 0 0). From the linear variation of the charge densities of this Cu-UPD peak with the step density, we conclude that Cu-UPD is related to the adsorption of Cu on (1 0 0) terrace sites. Hence Cu-UPD is a structural probe of (1 0 0) terrace sites on quasi-crystalline Ru films supported on platinum. In order to reduce the amount of oxygen-species blocking the Ru/Pt(1 1 1) and vicinal surfaces, diffusion controlled progressive over-potential deposition (OPD) of Cu (in the sub-monolayer regime but at very negative potentials) from very dilute Cu2+(aq) containing solutions was performed. For the Ru/Pt(1 1 1) film electrode, a desorption peak in the UPD range around 300 mV vs. Cu/Cu2+ for Cu desorption from the (1 1 1) sites was then observed, while for experiments on the Ru/Pt(3 1 1), Ru/Pt(5 1 1) and Ru/Pt(5 3 3) electrodes, we could also observe a peak at around 200 mV, which we ascribe to the desorption of Cu from the (1 0 0) oriented sites. From these experimental results, we conclude that after preparation of the Ru-film electrodes, the terrace and step sites of the underlying Pt single-crystal substrate are preserved on the Ru film. These results for Cu-UPD on the Ru-film electrodes also demonstrate that free Pt domains do not exist on the Ru-film electrodes.

Cyclic voltammetry (CV) has been used to investigate the irreversible adsorption of ethyl 2-oxopropanoate (ethyl pyruvate (EtPy)) on well-defined Pt and Pd electrodes. Following dosing of EtPy at open circuit on Pt and Pd surfaces, adsorption was found to be structure sensitive with extensive chemisorption being exhibited at {1 1 0} and {1 0 0} terraces together with {1 1 1} × {1 0 0} and {1 1 1} × {1 1 1} steps. However, only very limited adsorption of EtPy was observed at {1 1 1} terraces under identical dosing conditions. In particular, Pt{1 0 0} terraces were found to give rise to significant decarbonylation of molecularly adsorbed EtPy in the hydrogen underpotential deposition (H upd) potential region to generate chemisorbed CO. This finding concerning EtPy adsorption and decomposition agrees with previous investigations on polycrystalline Pt. In contrast, no electrochemical evidence for EtPy decomposition to form adsorbed CO on Pd was ever detected, irrespective of the surface crystallography of the electrode. EtPy decarbonylation was found to be suppressed on Pt{1 0 0} by pre-modification with (R)-[(4S, 5R, 7S)-5-ethenyl-1-azabicyclo[2.2.2]octan-7-yl]-quinolin-4-yl methanol (cinchonidine (CD)), often applied as a chiral modifier in the Pt-catalysed enantioselective hydrogenation of α-ketoesters. The degree of inhibition was found to be proportional to the amount of CD adsorbed. This surface sensitivity suggested that EtPy requires a very specific adsorption geometry or number of free Pt sites to undergo decarbonylation. For all surfaces studied, EtPy adsorption products could readily be removed either by electrochemical hydrogenation (leaving behind a clean metal surface) or, in the case of adsorbed CO, by performing potential excursions to 0.85 V (Pd/H) to facilitate electrooxidation of CO to CO2. The results highlight the relative importance of ‘active’ {1 1 0} and {1 0 0} defect sites (relative to {1 1 1} terraces) for the chemisorption of EtPy on polycrystalline Pt catalysts used in the enantioselective hydrogenation of α-ketoesters and this finding may have wider implications for catalyst design methodologies.

The cyclic voltammetric (CV) behaviour of gold adsorbed on Pt{h k l} electrodes is reported. It is found that stepped surfaces vicinal to Pt{1 1 1} exhibit preferential adsorption of gold at step sites. However, for stepped surfaces containing Pt{1 0 0} terraces, adsorption of gold at step and terrace site occurs with equal probability, although for Pt{n 1 1} electrodes with n < 7 (i.e. electrodes containing short Pt{1 0 0} terraces), slight preference for step site adsorption is still observed. This behaviour is similar to that reported previously for Bi adsorption on Pt{h k l} and is interpreted in terms of slower rates of gold atom surface diffusion across Pt{1 0 0} vs. Pt{1 1 1} terraces. By comparing the electrochemical response of gold adlayers on Pt{h k l} with previously published bulk Au{h k l} voltammetry, it is deduced that the gold overlayers on Pt{h k l} are pseudomorphic in nature. This finding is in agreement with previous UHV and electrochemical results for gold deposition on platinum. Using such gold modified Pt{h k l} electrodes as model surfaces, we also report, for the first time, the electrooxidation of ethanol on Au/Pt{h k l} in alkaline aqueous solution. The ethanol oxidation reaction (EOR) is shown to be structure sensitive for submonolayer gold coverages. In fact, a maximum in the rate of EOR at platinum sites adjacent to gold islands is observed between approximately 0.4–0.6 monolayers of gold on Pt{1 0 0}, Pt{1 1 1} and Pt{1 1 0} in 0.1 M NaOH(aq). A second electrooxidation state at more positive potentials for 0 < θAu < 1 ascribed to EOR at pure gold sites is also observed, at least for Pt{1 1 1} and Pt{1 0 0}. On Pt{1 1 1}, the potential range and activity of EOR in this second process is similar to bulk gold whereas for submonolayer gold films on Pt{1 0 0}, the peak is shifted to more negative potentials.

The formation of quasi-crystalline PtRh two dimensional films supported on Pt{1 0 0} is described. For the first time, the voltammetry of PtRh{1 0 0} single crystal alloys covering the whole range of alloy composition is reported. Synthesis follows a similar procedure to that described previously for the formation of PtPd alloys supported on Pt{h k l} but with some important provisos concerning the final annealing step. CO electrooxidation was used as a probe reaction and for certain PtRh{1 0 0} surface alloys, unusually high electrocatalytic activity was observed relative to monometallic Pt and Rh electrodes. The flame annealing of a “PtRhPt sandwich” precursor structure was found to be the best method of forming the PtRh alloy surfaces. For PtRh films annealed under nitrogen, significant phase separation was observed in agreement with previous surface science studies of PtRh adlayers on Pt{1 0 0} annealed in the absence of oxygen. In addition, an excess of Rh in the “sandwich structure” from which the alloy was formed tended to preclude good alloy formation. It is suggested that the protocols for thin film formation described may prove useful in many other important electrocatalytic systems.

A detailed study of the hydrochlorination of acetylene and higher alkynes using a supported gold catalyst is described and discussed. A series of reactions using sequential exposure of the catalysts to C2H2 and HCl demonstrate that exposure to HCl prior to reaction of C2H2/HCl leads to enhanced activity whereas exposure to C2H2 leads to deactivation. The reaction of higher alkynes is affected by steric factors with the trend in activity being: acetylene (ca. 40 % conversion)>> hex-1-yne (10%)>phenylacetylene (7 %) > hex-2-yne (2 %) under standard reaction conditions. Using 1H-NMR spectroscopy we have found that for hex-1-yne and phenyl acetylene the anti-Markovnikov product is \ud formed by anti addition of HCl. However, the Markovnikov products are equivalent for syn- and antiaddition of HCl, and hence we investigated the reaction using deuterated substrates and confirmed the products are formed by the anti addition of HCl. The reaction mechanism is discussed in detail.

In a recent communication [F.J. Vidal-Iglesias, A. Al-Akl, D.J. Watson, G.A. Attard, Electrochem. Commun. 8 (2006) 1147], we demonstrated via a combination of forced deposition and flame-annealing procedures that PtPd{1 1 0} single crystal alloy films may be prepared using Pt{1 1 0} as a surface template. The present study extends the application of such protocols to the general case of PtPd{hkl}. Characterization of the well-defined PtPd surface alloy films using cyclic voltammetry (CV) and copper underpotential deposition (Cu UPD) allows quantification of the surface alloy composition based on systematic variations in the voltammetric signatures (charge and peak potential) corresponding to Pt-rich and Pd-rich regions of the electrode surface. Comparison with previous Auger/LEED/CV measurements of alloy composition using bulk PtPd{hkl} electrodes [D.J. Watson, G.A. Attard, Surf. Sci. 515 (2002) 87, T.J. Schmidt, N.M. Markovic, V. Stamenkovic, P.N. Ross Jr., G.A. Attard, D.J. Watson, Langmuir 18 (2002) 6969] provides a number of insights into the structure of the alloy surface and the veracity of the electrochemical estimation of surface composition. For PtPd{1 1 1} electrodes, excellent agreement between electrochemical and surface science determinations is observed. This suggests that the original assumption used in the Auger analysis of a homogeneous PtPd film, was correct. However, for the more open PtPd{1 0 0} and PtPd{1 1 0} surfaces, the disagreement between electrochemical and Auger analyses was more marked. We suggest that in these cases, the assumption of a completely homogeneous selvedge is not correct and strong surface segregation of Pd results in an oscillatory compositional profile as reported for several other Pt binary alloy electrodes.

Microbial reduction of Au(III) from HAuCl4 was demonstrated. Escherichia coli and Desulfovibrio desulfuricans reduced 1 mM Au(III) in 60 and 120 min at pH 6.9 and 2.3 respectively. TEM and elemental analysis showed the formation of Au(0) nanoparticles and their pH-dependent cellular localisation. The concept was applied to the recovery of gold from jewellery waste leachates using E. coli. Bio-Au(0) nanoparticles were tested for catalytic activity in the oxidation of glycerol, achieving 30% conversion to glyceric acid. A simple bioprocess for conversion of waste to new material is suggested.

Carbon nanocages, with remarkably large mesoporous volumes, have been synthesized by the deposition of p-xylene over a Co/Mo catalyst in supercritical carbon dioxide. Nanocages with diameters ranging between 10 and 60 nm were synthesized at temperatures between 650 and 750 degrees C. The surface area and pore volume of the nanocages produced was found to depend on the reaction temperature and pressure employed. In particular, carbon nanocages with a pore volume of up to 5.8 cm(3) g(-1) and a BET surface area of 1240 m(2) g(-1) were readily synthesized at a temperature of 650 degrees C and a pressure of 10.34 MPa. The high pore volume and surface area of the carbon nanocages synthesized makes them ideal materials for use as inert adsorbents and catalytic supports.

Cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS) have been used to characterise novel PtRh\ud mixed metal and surface alloyed active phases supported on 5% Pt/graphite catalysts (5% Pt/G). The active phases\ud could be prepared using forced deposition or a combination of forced deposition and thermal annealing in a\ud flowing 5% hydrogen in argon gas mixture at 700 K. The protocols employed originate directly from previous\ud single crystal studies of Rh on Pt{100} whereby Rh overlayers (either singly adsorbed or as a ‘sandwich structure’\ud of alternate Pt/Rh/Pt layers) could be transformed into surface PtRh alloys by careful thermal annealing. We\ud demonstrate that this method is also successful for the preparation of active supported catalysts for CO\ud electrooxidation whereby a peak potential as low as 0.60 V (Pd/H) for the CO oxidation is reported (0.12 V\ud lower than that on 5% Pt/G). Moreover, the onset potential for CO stripping is lowered to 0.33 V (Pd/H). The\ud presence of alloyed PtRh phases gives rise to a small but reproducible 0.1–0.2 eV shift to higher binding energy\ud of the Pt 4f7/2 XPS peak together with strongly modified Pt and Rh electrosorption features in the CV which\ud correlate with changes in surface composition. Unusual kinetic behaviour in the CO stripping peaks from the\ud PtRh catalyst as a function of CO coverage is ascribed to competition between electrochemical oxide on Rh and\ud CO-induced blocking of electrochemical oxide formation sites at the highest CO coverage. For PtRh alloys, the\ud onset of electrochemical oxide formation shifts to more positive potentials relative to Rh overlayers and so a\ud different behaviour towards CO electrooxidation is observed.

A new method for the preparation of Ru quasi single crystal electrode surfaces is described. Using the ‘forced deposition’ method followed by resistive heating in nitrogen, it is demonstrated that well-defined Ru films supported on Pt single crystal electrodes may be synthesised which, for the case of Pt{111} exhibit voltammetry similar to that reported for bulk single crystal Ru(0001) electrodes. Moreover, systematic changes in the voltammetric response of the well-ordered supported Ru film upon varying the substrate surface crystallography from Pt{111} to Pt{100} (via a series of Pt n{111} × {100} and Pt n{100} × {111} stepped surfaces) demonstrate unequivocally the epitaxial nature of the films. For surfaces based on Pt{100} – (1 × 1) terraces, two sharp, intense peaks just positive of the potential of hydrogen evolution signify the presence of fcc Ru{100} terrace sites. This is significant because fcc {100} surface sites are not normally associated with hcp bulk phases. In addition, the voltammetric features usually ascribed to fcc {100} × {111} step sites and {111} terraces are clearly identified for the Ru films. The surfaces prepared by this method have been characterised by cyclic voltammetry (CV) in H2SO4. The most interesting facet of this new method is the ease of preparation of fcc Ru{hkl} surfaces relative to analogues derived from variously prepared single crystals of Ru. Keywords: Single crystal electrodes, Cyclic voltammetry, Ruthenium single crystal surfaces

A new method for the preparation of PtPd single crystal alloy surfaces is described. Using the ‘forced deposition’ method followed by gentle flame annealing, it is demonstrated that well-defined epitaxial PtPd surface alloy films supported on Pt single crystal electrodes may be synthesised covering the whole range of surface alloy composition. The surfaces prepared by this method have been characterised by cyclic voltammetry (CV) in H2SO4 and also via copper underpotential deposition (Cu UPD). The most interesting facet of this new method is the ease of preparation of PtPd{hkl} alloy surfaces relative to analogues derived from bulk PtPd single crystals, although in this paper, only the characterisation of PtPd{110} is presented. Keywords: Single crystal electrodes, Cyclic voltammetry, Platinum–palladium alloys

A 5% Pt/graphite catalyst has been sintered in 5% H2/Ar at 400, 500, 600, 700, 800, and 1000 K and cinchonidine-modified samples used to catalyse enantioselective ethyl pyruvate hydrogenation at 293 K and 30 bar pressure. Changes in catalyst morphology on sintering have been investigated by high resolution electron microscopy and cyclic voltammetry. The as-received catalyst contained small Pt particles aggregated into clusters. As the temperature was raised these clusters disaggregated; the resulting small particles grew, first showing enhanced crystallinity and better defined step and terrace topography, and later progressive faceting. Ultimately the particles were large and hexagonal. These processes were accompanied by a loss of surface area and a reduction in catalytic activity. Enantiomeric excess rose from 43% for as-received material to 63% for catalyst sintered at 700 K, and declined for higher sintering temperatures. The particle size distribution for the optimal catalyst peaked at 8 nm and most particles were substantially faceted. Chiral performance is interpreted in terms of enhanced enantioselectivity provided by edge sites in the Pt surface. Modification of chiral kink sites by alkaloid, to give diastereomeric enantioselective sites may have further enhanced the enantioselectivity. The investigation provides clear objectives for future catalyst design.

Since there has been no effort at all in using a microwave cavity resonator in the detection of hydrogen peroxide in water, we propose a simple detection method of hydrogen peroxide concentration based on the well-known microwave cavity perturbation technique for the TM010 mode at of a copper cylindrical cavity at 3.48 GHz. From the measurements, we found that the main parameters for cavity perturbation namely center frequency shifts and bandwidth (or quality factor Q) changes both exhibit strong correlation with the concentration.

The steps (Pt{111} × {111} and Pt{100} × {111}) and terraces (Pt{100} and Pt{111}) of a 5% Pt/graphite catalyst have been identified by cyclic voltammetry and their contributions to rate and enantioselectivity in high-pressure ethyl pyruvate hydrogenation assessed. Bi preferentially adsorbed from solution onto the platinum surface of the catalyst at step and {100} terrace sites. Further increasing Bi coverage led to the gradual occupation of {111} terrace sites, followed by the formation of Bi multilayers. In contrast, S adsorbed from solution onto terrace and step sites simultaneously but with the {111} × {111} step sites being strongly disfavoured. Pt/graphite, Bi–Pt/graphite, and S–Pt/graphite catalysts have been modified by cinchonidine and used to catalyse the enantioselective hydrogenation of ethyl pyruvate to ethyl lactate at 30 bar and 293 K. The effect of increasing Bi coverage at step sites was to increase activity substantially but reduce enantiomeric excess from 43%(R) to 17%(R), whereas the effect of increasing S adsorption at terrace sites was to decrease activity and increase enantiomeric excess to 52%(R). These unexpected contrary effects on activity and enantioselectivity were confirmed for Bi adsorption by repeating the experiments using the standard reference catalyst 6.3% Pt/silica (EUROPT-1), for which enantiomeric excess fell linearly from 73%(R) to 20%(R) as Bi loading was increased. The well-documented rate enhancement associated with catalyst modification by cinchonidine has been reassessed in the light of this further rate enhancement by Bi adsorption, and its origin has been attributed to inhibition of ethyl pyruvate dimerisation/polymerisation by the strongly basic alkaloid. Rate enhancement is now attributed to reaction occurring at a normal rate at an enhanced number of sites, not (as previously proposed) to a reaction occurring at an enhanced rate at a constant number of sites. The opposing effects of Bi and S on rate and enantioselectivity are consistent with (i) preferential initiation of pyruvate polymerisation at step sites, (ii) inhibition of propagation of this polymerisation by alkaloid, and (iii) a higher enantiomeric excess in cinchonidine-modified near-step sites than in similarly modified terrace sites. These results have important implications for future catalyst design.