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CO2 electroreduction has been considered a promising alternative to simultaneously reduce CO2 emissions and produce value-added products. Among others, the production of formic acid/formate is particularly attractive. Although promising results have already been obtained in the literature, one of the recent approaches to improve the process deals with the use of an alternative reaction at the anode instead of the traditional oxygen evolution reaction (OER). In this context, this work reports, for the first time, the study of the CO2 electroreduction to formate coupled with the electrooxidation of glycerol to high-added value products where both half-reactions operate in a continuous mode with a single pass of the reactants through the electrochemical cell. Interestingly, at the cathode, similar results to those previously reported were obtained, reaching formate concentrations of about 18 g·L-1 at a 200 mA·cm-2. In addition, at the anode, promising dihydroxyacetone productions of 196 µmol·m-2·s-1 were simultaneously achieved in the output stream of the anodic compartment. These findings represent a significant step forward for the development and application of the technology. The authors gratefully acknowledge financial support through projects PID2019–108136RB-C31, PID2019–108136RB-C32 and PID2020–112845RB-I00 (AEI/10.13039/501100011033).

An autonomous electrochemical system prototype for ammonia oxidation reaction (AOR) measurements was efficiently done inside a 4'' x 4'' x 8'' 2U Nanoracks module at the International Space Station (ISS). This device, the Ammonia Electrooxidation Lab at the ISS (AELISS), included an autonomous electrochemical system that complied with NASA ISS nondisclosure agreements, power, safety, security, size constrain, and material compatibility established for space missions. The integrated autonomous electrochemical system was tested on-ground and deployed to the International Space Station as a “proof-of-concept” ammonia oxidation reaction testing space device. Here are discussed the results of cyclic voltammetry and chronoamperometry measurements done at the ISS with a commercially available channel flow-cell with eight screen-printed electrodes, including Ag quasi-reference (Ag QRE) and carbon counter electrodes. Pt nanocubes in Carbon Vulcan XC-72R were used as the catalyst for the AOR and 2 μL drop of Pt nanocubes/ Carbon Vulcan XC-72R, 20 wt%, ink was placed on the carbon working electrodes and allowed to dry in air. After the AELISS was prepared for launch to the ISS, a 4 days delayed (2 days in the space vehicle Antares and 2 days space transit to the ISS) cause a slight shift on the Ag QRE potential. Nevertheless, the AOR cyclic voltametric peak was observed in the ISS and showed ca. 70% current density decrease due to the buoyancy effect in agreement with previous microgravity experiments done at the zero-g aircraft. This work was supported by the Puerto Rico NASA Space Grant Consortium, funded through the NASA Cooperative Agreement Grant Number 80NSSC20M0052, NASA-EPSCoR-International Space Station (ISS) Flight Opportunity Grant Number NNH14ZHA002C, NASA-RID Grant Number 80NSSC19M0049, and the National Science Foundation (NSF) CREST Center for Innovation Research and Education in Environmental Nanotechnology Grant Number 1736093. C.R.C acknowledges the STARs Award (2021) of the University of Texas System.

Shape‐controlled metal nanoparticles are significantly improving the electrocatalysis of many relevant reactions. By controlling the shape of nanoparticles, it is possible to engineer their surface to exhibit a preferential structure. However, to facilitate the incorporation of shaped nanomaterials into practical electrochemical devices, it is indispensable to overcome limitations caused by their large particle size (typically >5 nm). For practical applications, nanoparticles must have a size lower than 5 nm with a clean surface to decrease costs and provide a sufficiently large specific surface area. This is a major challenge that has remained unexplored up to now. Herein, we present the synthesis and electrochemical characterization of 3–5 nm, with well‐defined cubic Pt nanoparticles supported on carbon. The electrochemical characterization of the nanoparticles evidences the existence of a preferential {100} and clean structure (within about 40 % of {100} terrace surface). This paper was performed under Ministerio de Ciencia e Innovación-FEDER (Spain) Project PID2019-105653GB-100 and Generalitat Valenciana (Project PROMETEO/2020/063). J.S.G. thanks VITC (Vicerrectorado de Investigación y Transferencia de Conocimiento) of the University of Alicante (UATALENTO16-02). R.M.A and R.M.T thank to the support from FAPESP, Procs. 2019/08051-0, 2017/15469-5 and 15/26308-7. H.E. thanks the Estonian Research Council (grant No PUTJD841).

Human activities during the last century have increased the concentration of greenhouse gases in Earth's atmosphere, mainly carbon dioxide (CO2), and the impacts of climate change around the world are becoming more damaging. Therefore, scientific research is needed to mitigate the consequences of atmospheric CO2, and, among others, the electrochemical CO2 conversion to useful chemicals is one of the most interesting alternatives. Herein, different Bi, Sn and Sb systems were synthesised as nanoparticles, supported on carbon (Vulcan XC-72R) and finally used to manufacture electrodes. The Bi-Sn-Sb nanoparticulated systems and their corresponding electrodes were characterised by TEM, XPS, ICP-OES and SEM. Electrochemical reduction of CO2 to formate was performed in an electrochemical H-type cell in a CO2-saturated KHCO3 and KCl solution. The Bi-Sn-Sb electrodes exhibited good activity and selectivity for the CO2 reduction towards formate. Particularly, Bi95Sb05/C and Bi80Sn10Sb10/C electrodes showed improved stability compared to previous works, keeping values of formate efficiency over 50 % after 24 h. This research was funded by the MICINN Spanish Ministry, through the projects CTQ2016-76231-C2-2-R (AEI/FEDER, UE) and PID2019-108136RB-C32.

The lack of an artificial system that mimics elemental sulfur (S8) oxidation by microorganisms inhibits a deep mechanistic understanding of the sulfur cycle in the biosphere and the metabolism of sulfur-oxidising microorganisms. In this article, we present a biphasic system that mimics biochemical sulfur oxidation under ambient conditions using a liquid|liquid (L|L) electrochemical cell and gold nanoparticles (AuNPs) as an interfacial catalyst. The interface between two solvents of very different polarity is an ideal environment to oxidise S8, overcoming the incompatible solubilities of the hydrophobic reactants (O2 and S8) and hydrophilic products (H+, SO32–, SO42–, etc.). Furthermore, the interfacial AuNPs provide a catalytic surface onto which O2 and S8 can adsorb. Control over the driving force for the reaction is provided by polarising the L|L interface externally and tuning the Fermi level of the interfacial AuNPs by the adsorption of aqueous anions. Comparison of electrochemical measurements using a 4-electrode closed bipolar electrochemical cell and a L|L electrochemical cell confirmed that electron transfer reactions are possible between O2, gold and S8 in biphasic systems. M.D.S. acknowledges Science Foundation Ireland (SFI), under Grant No. 13/SIRG/2137 and the European Research Council through a Starting Grant (Agreement No. 716792). M.F.S.-H. acknowledges the “Universidad Nacional de Colombia” for allowing his sabbatical leave and the “Fundación Banco de la República” through the grant 4.562.

The adsorption of p-nitroaniline (PNA) on Pt nanoparticles, both in the absence (in aqueous solution) and in the presence of oxygen (in air environment), is studied by SERS for the first time. Differences between the plasmon-driven catalysis of adsorbed PNA on Pt and Ag nanoparticles have been found. In the presence of oxygen, the oxidative coupling of the NH2 group in PNA to yield dinitroazobenzene (DNAB) occurs on both Pt and Ag nanoparticles. However, in the absence of oxygen, PNA behaves clearly differently on Ag than on Pt. Thus, whereas diaminoazobenzene (DAAB) is catalytically produced on Ag nanoparticles by plasmon-driven reduction reactions of the NO2 group, on Pt nanoparticles this reaction does not fully take place as indicated by the presence of NO2 groups on the surface of the nanoparticles. A mechanism for this distinctive behavior is tentatively proposed in which water acts as a sacrificial agent, being reduced to hydrogen by hot electrons coming from the Pt surface, while the hot holes on Pt are proposed to attach to an occupied molecular state of adsorbed PNA. The overall photocatalytic reaction of adsorbed PNA on Pt nanoparticles, in an O2 free solution, would actually be consistent with a dehydrogenation process of water. This work was conducted under the framework of the Spanish Ministry of Economy, Industry and Competitiveness (MINECO), project CTQ2016-76231-C2-2-R (AEI/FEDER, UE). JSG acknowledges financial support from VITC (Vicerrectorado de Investigación y Transferencia de Conocimiento) of the University of Alicante (UATALENTO16-02).

The use of shape-controlled nanomaterials represents an elegant way to improve the performance of many electrochemical reactions. However, two main aspects must be still optimised: decreasing particle size and increasing their activity. This study shows that the deposition of Pd on different small (3-5 nm) supported Pt materials (displaying a preferential structure containing ∼40% of Pt{100} terraces) leads to a great enhancement in the electrocatalytic activity towards the formic acid electrooxidation reaction. After Pd decoration, the oxidation takes place at lower overpotentials and oxidation current densities are significantly higher than those observed with all the bare Pt/C samples. For the Pt/C 45% catalyst, the intrinsic activity after Pd deposition was more than three times of that without Pd, while the oxidation overpotential shifted about ∼200 mV to lower overpotentials. This work was supported by the Ministerio de Ciencia e Innovación-FEDER (Spain) Project PID2019-105653GB-100 and Generalitat Valenciana (Project PROMETEO/2020/063). R.M.A and R.M.T thank to the support from FAPESP, Procs. 2019/08051-0, 2017/15469-5 and 15/26308-7. H.E. thanks the Estonian Research Council (grant No PUTJD841).

The understanding of electrocatalytic activity and poisoning resistance properties of Pt and Pd nanoparticles, recognized as the best electrocatalysts for the ethanol oxidation reaction, is an essential step for the commercialization of direct ethanol fuel cells (DEFCs). In this paper, mono and bimetallic Pt and Pd nanoparticles with different atomic ratios have been synthesized to study their electrocatalytic properties for an ethanol oxidation reaction in alkaline solutions. The different nanoparticles were physiochemically characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The electrochemical characterization was performed by cyclic voltammetry and chronoamperometry measurements. The electrochemical measurements indicate that Pt nanoparticles have much higher electrocatalytic activity for ethanol oxidation than Pd nanoparticles. The studies with bimetallic PtPd nanoparticles showed a significant impact of their composition on the ethanol oxidation. Thus, the highest electrocatalytic activity and poisoning resistance properties were obtained for Pt3Pd2 nanoparticles. Moreover, this study demonstrates that the poisoning of the catalyst surface through ethanol oxidation is related to the prevalence of the acetaldehyde–acetate route and the polymerization of acetaldehyde through aldol condensation in the alkaline media. This research was funded by Ministerio de Ciencia e Innovación (Spain) grant number PID2019-105653GB-100), Generalitat Valenciana (Spain) grant number PROMETEO/2020/063, and the University of Zanjan Research Council.

Electrocatalysis is at the heart of a broad range of physicochemical applications that play an important role in the present and future of a sustainable economy. Among the myriad of different electrocatalysts used in this field, nanomaterials are of ubiquitous importance. An increased surface area/volume ratio compared to bulk makes nanoscale catalysts the preferred choice to perform electrocatalytic reactions. Bragg coherent diffraction imaging (BCDI) was introduced in 2006 and since has been applied to obtain 3D images of crystalline nanomaterials. BCDI provides information about the displacement field, which is directly related to strain. Lattice strain in the catalysts impacts their electronic configuration and, consequently, their binding energy with reaction intermediates. Even though there have been significant improvements since its birth, the fact that the experiments can only be performed at synchrotron facilities and its relatively low resolution to date (∼10 nm spatial resolution) have prevented the popularization of this technique. Herein, we will briefly describe the fundamentals of the technique, including the electrocatalysis relevant information that we can extract from it. Subsequently, we review some of the computational experiments that complement the BCDI data for enhanced information extraction and improved understanding of the underlying nanoscale electrocatalytic processes. We next highlight success stories of BCDI applied to different electrochemical systems and in heterogeneous catalysis to show how the technique can contribute to future studies in electrocatalysis. Finally, we outline current challenges in spatiotemporal resolution limits of BCDI and provide our perspectives on recent developments in synchrotron facilities as well as the role of machine learning and artificial intelligence in addressing them. Financial support from Brazilian agencies: P.S.F. thanks FAPESP (Grants 2017/11986-5, 2018/20952-0, and 2019/13888-6 (RAV fellowship)), CNPq (Grant136436/2019-6 (RAV fellowship)), Shell, and the strategic importance of the support given by ANP (Brazil’s National Oil, Natural Gas and Biofuels Agency) through the R&D levy regulation. Use of the Center for Nanoscale Materials, an Office of Science user facility, was supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences Data, Artificial Intelligence and Machine Learning at DOE Scientific User Facilities program under Award No. 34532.

Bragg coherent diffraction imaging is a powerful strain imaging tool, often limited by beam-induced sample instability for small particles and high power densities. Here, we devise and validate an adapted diffraction volume assembly algorithm, capable of recovering three-dimensional datasets from particles undergoing uncontrolled and unknown rotations. We apply the method to gold nanoparticles which rotate under the influence of a focused coherent x-ray beam, retrieving their three-dimensional shapes and strain fields. The results show that the sample instability problem can be overcome, enabling the use of fourth generation synchrotron sources for Bragg coherent diffraction imaging to their full potential. Research conducted at MAX IV, a Swedish national user facility, is supported by the Swedish Research council under Contract No. 2018-07152, the Swedish Governmental Agency for Innovation Systems under Contract No. 2018-04969, and Formas under Contract No. 2019-02496. This work has also received funding from the ÅForsk Foundation (Contract No. 17-408), the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Contract No. 801847), from the Olle Engkvist Foundation, from the Swedish Research council (Contract No. 2018-00234), and from NanoLund.

The application of shape-controlled metal nanoparticles in electrocatalysis has improved significantly the activity, selectivity, and even the stability of many relevant electrocatalytic reactions. It is well accepted that, by controlling the shape of the nanoparticles, it is possible to provide nanoparticles with a preferential surface structure. However, to fully understand the capabilities of these nanomaterials, it is extremely relevant to correlate shape, surface structure, and electrocatalytic reactivity. Particularly, establishing the correlations between surface structure and reactivity is the key point to be studied and understood. Consequently, having tools to characterize the surface structure of these nanoparticles is of critical importance. In this short review, we discuss about the progress in the in situ characterization of the surface structure of shaped Pt, Au, and Pd nanoparticles by electrochemical probes. The results here included clearly demonstrate the potentialities of the electrochemical tools to gain detailed information of the surface structure of these shaped nanomaterials. This article was performed under Ministerio de Ciencia e Innovación (MICINN)-FEDER (Spain) Project CTQ2016-76221-P. J.S-.G. also acknowledges financial support from VITC (Vicerrectorado de Investigación y Transferencia de Conocimiento) of the University of Alicante (UATALENTO16-02).

Previous knowledge shed by single crystal electrochemistry path the way to obtain better catalysts aiming fuel cell purposes. In this sense, tailoring shape-controlled nanoparticles has been a strategy followed over the past years to optimize the activity, selectivity and stability of electrocatalytic surface sensitive reactions by maximizing the exposure of certain facets of the nanocatalyst. In the present paper, preferentially oriented (100) nanoparticles synthesized by different methodologies have been electrochemically characterized and compared. The voltammetric profile of these cubic nanoparticles has also been compared with different platinum single crystal stepped surfaces, showing a singular fitting to the characteristic response of Pt(510). Subtle changes on the surface structure of platinum nanocubes due to surface degradation upon storage time in aqueous solution are pointed out in this work. The characteristic fingerprints of platinum surfaces and CO oxidation profiles have demonstrated to be powerful surface probes for the in situ detection of these minor structural reorganizations. This work has been supported by the Ministry of Economy and Competitiveness (MINECO) through the project CTQ2016-76221-P and Generalitat Valenciana (project PROMETEO II/2014/013). J.S.G. acknowledges financial support from VITC (Vicerrectorado de Investigación y Transferencia de Conocimiento) of the University of Alicante.

In this work, Vulcan carbon-supported cube-shape Pt nanoparticles with various metal loadings were synthesised in the presence of oleylamine and oleic acid. Surface morphology of different Pt/C samples was examined by transmission electron microscopy (TEM) and their metal loading verified by thermogravimetric analysis (TGA). TEM micrographs showed Pt nanoparticles with a preferential cubic-shape and increased agglomeration of the particles with increasing Pt loading. Electrochemical characterisation of the Pt/C catalysts indicated that the resulting Pt nanoparticles present a preferential (100) surface structure. The electrocatalytic properties of the Pt/C catalysts of different metal loading were evaluated towards the oxygen reduction reaction (ORR) both in acidic and alkaline media employing the rotating disk electrode (RDE) configuration. Interestingly, similar specific and mass activities were found in both solutions revealing that the ORR activities were independent of the Pt loading and suggesting that all the Pt nanocubes contributed as isolated particles. This work was financially supported by institutional research funding (IUT20-16) of the Estonian Ministry of Education and Research. This research was also supported by the EU through the European Regional Development Fund (TK141 “Advanced materials and high-technology devices for energy recuperation systems”). KJ would like to thank Archimedes Foundation for the partial study scholarship. JMF thanks MINECO (Project CTQ2016-76221-P (AEI/FEDER, UE)) and Generalitat Valenciana (Project PROMETEOII/2014/013) for financial support. JSG acknowledges financial support from VITC (Vicerrectorado de Investigación y Transferencia de Conocimiento) of the University of Alicante.

Formic acid electrooxidation on Tl modified Pt single crystal electrodes has been carried out in sulfuric acid media. Voltammetric experiments demonstrated that Pt(100) modified by Tl displays a significant enhancement towards formic acid oxidation both lowering the oxidation onset potential and increasing the maximum current density in the positive going-sweep. A similar behavior has been observed in Pt(s)[(100)x(111)] stepped surfaces. On the other hand, for Pt(111) surfaces, the incorporation of Tl also induced a shift of the oxidation onset to lower potential values, a diminution of the hysteresis between the positive and negative going-sweep and also an increase of the oxidation currents. These results have been corroborated using in situ FTIR experiments, where the CO adsorption band disappears completely when Pt(100) and its vicinal surfaces are modified by Tl adatom, leading to the formation of CO2 at lower overvoltages. This work has been financially supported by the MINECO (Spain) (projects CTQ2013-44083-P and CTQ2013-48280-C3-3-R) and Generalitat Valenciana (project PROMETEOII/2014/013, FEDER).

This is a study of the chronoamperometric performance of the electrochemical oxidation of ammonia in an alkaline fuel cell for space applications. Under microgravity the performance of a fuel cell is diminished by the absence of buoyancy since nitrogen gas is produced. The following catalysts were studied: platinum nanocubes of ca. 10nm, platinum nanocubes on carbon Vulcan ™ and platinum on carbon nanoonion support of ca. 10nm. These nanomaterials were studied in order to search for catalysts that may reduce or counter the loss of ammonia oxidation current densities performance under microgravity conditions. Chronoamperometries at potential values ranging from 0.2 V to 1.2V vs. cathode potential (breathing Air/300ml/min/82737 Pa) in 1.0 M NH4OH (30ml/min in anode) were done during over 30 parabolas in NASA’s C9 airplane The Weightless Wonder in January 2016 from Ellington Field Houston. The current densities at 15s in the chronoamperometry experiments showed diminishing values under microgravity and in some cases improvements of up to 92%, for Pt-carbon nanoonions, and over 70% for the three catalysts versus ground at potentials ranging from 0.2 to 0.4V after 5 minutes of chronoamperometric conditions. At higher potentials, 1.0V or higher, Pt nanocubes and Pt-carbon nanoonions showed enhancements of up to 32% and 24%, respectively. At these higher potentials we will have a contribution of oxygen evolution. The changes in current behavior are attributed to the sizes of the catalyst materials and the time needed for the N2 bubbles detachment from the Pt surface under microgravity conditions. This work was financially supported by the NASA-MIRO Center for Advanced Nanoscale Materials at the University of Puerto Rico-Río Piedras Campus Grant number NNX10AQ17A and NASA-EPSCoR grant number NNX14AN18A, Puerto Rico NASA Space Grant Consortium: NASA cooperative agreement NNX10AM80H, NASA Flight Opportunities Program Announcement of Flight Opportunities (AFO) NOCT110 call #5 and Ministerio de Economía y Competitividad (projects CTQ2013-44083-P and CTQ2013-48280-C3-3-R).

Electrochemical denitrification is a promising approach to remove NO3− towards its conversion to innocuous N2. In this work, the electrocatalytic performance of Bi, Sn and BixSny carbon-supported nanoparticles (∼10 nm) was evaluated for the selective NO3− electroreduction (NER) to N2. The different electrocatalysts were synthesised using a simple chemical method, physicochemically characterised by TEM-EDS and XPS and, subsequently, air-brushed onto a Toray carbon paper to build electrodes. These electrodes were characterised by SEM-EDS and cyclic voltammetry. Electrolyses were carried out in a slightly alkaline media to find the most active electrocatalyst towards the NO3− removal. Among them, Bi60Sn40/C showed the best results with more than 50% of selectivity to N2 after exhaustive electrolyses, regardless of the cathode potential or the electric charge passed. Other detected non-desired secondary products were N2O, NO2− and NH4+/NH3. The results obtained point out that the combination of Sn and Bi gives rise to higher NER activity and selectivity to N2 than pure Bi and pure Sn. Therefore, these electrocatalysts are not only promising but also cost-effective for future practical applications like electrochemical denitrification of wastewater. Nevertheless, further investigation is still needed in order to assess the optimum operational conditions. I. Sanjuán acknowledges the Ph.D. fellowship granted and the material and human resources provided by the University of Alicante and the company Aguas de Valencia, S.A (UAIND2016-02). JSG acknowledges financial support from VITC (Vicerrectorado de Investigación y Transferencia de Conocimiento) of the University of Alicante (UATALENTO16-02).

The practical application of Pt-based technologies depends on the lowering in the costs and one way to face this challenge is by reducing the amount of Pt. Herein, we decorate Ag nanoparticles with ultra-small (0.8 %) quantities of Pt and test them for the electrooxidation of glycerol. We showed that the Pt atoms of our catalyst are one order of magnitude more active (in terms of mass activity) than Pt/C commercial catalyst. By performing in situ FTIR measurements, electrolysis experiments and HPLC analysis, we showed that both catalysts form mainly glycerate and lactate, but Pt/C is more prone to poisoning and to form carbonate. We suggest that this different behavior is attributed to the high dispersion of the Pt atoms on Ag nanoparticles. The lower probability of finding neighboring Pt atoms diminishes the formation of multiple bonded intermediates, which are precursors for the formation of carbonate and some poisoning intermediates. PSF thanks Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) (grants: 2016/01365-0, 2017/11986-5, 2018/20952-0). CCL thanks Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001. J.S-G. also acknowledges financial support from VITC (Vicerrectorado de Investigación y Transferencia de Conocimiento) of the University of Alicante (UATALENTO16-02). We also thanks Prof. M.A. Zezzi and Luana F. da Costa for the ICP analysis. The authors also extend gratitude to CNPEM open-facilities (LME, and LNNano) and Synchrotron Light Laboratory, CNPEM/MCTIC under proposals 20180571 and 20171115.

The use of bismuth‐based catalysts is promising for formate production by the electroreduction of CO2 captured from waste streams. However, compared to the extensive research on catalysts, only a few studies have focused on electrochemical reactor performance. Hence, this work studied a continuous‐mode gas–liquid–solid reaction system for investigating CO2 electroreduction to formate using Bi‐catalyst‐coated membrane electrodes as cathodes. The experimental setup was designed to analyze products obtained in both liquid and gas phases. The influence of relevant variables (e.g., temperature and input water flow) was analyzed, with the thickness of the liquid film formed over the cathode surface being a key parameter affecting system performance. Promising results, including a high formate concentration of 34 g/L with faradaic efficiency for formate of 72%, were achieved. The authors of this work would like to acknowledge the financial support from the MINECO through the projects CTQ2016-76231-C2-1-R and CTQ2016-76231-C2-2-R (AEI/FEDER, UE). JSG acknowledges financial support from VITC (Vicerrectorado de Investigación y Transferencia de Conocimiento) of the University of Alicante (UTALENTO16-02).

The electron-induced damage in self-assembled monolayers (SAMs) of n-dodecanethiolate on Au(111) and Au(100) single-crystalline surfaces is investigated in situ by X-ray photoelectron spectroscopy. The same irradiation dose produced different adsorbed groups. The damage at the headgroup–substrate interface leads to find dialkyl sulfide (RS–R′) on Au(111), while dialkyl disulfide (RS–SR) and/or thiol (RSH) were produced on Au(100). With regard to C species, significant amounts of C═C are generated on Au(111) but not on Au(100), showing that double bond formation is not triggered through the same pathways on these surfaces. Detailed analysis of a variety of mechanisms, which involved cationic (RS+), anionic (RS–), or thiyl radical (RS•) species, in combination with ab initio density functional theory (DFT) calculation, leads to the conclusion that the radical pathways successfully explain the experimental results. Molecular dynamics simulations show that the n-dodecanethiolate SAMs on both surfaces are equivalent with regard to the van der Waals interactions. The breakage of the S–Au bonds is studied by means of DFT calculations. The thiyl radical would form close to the Au(100) surface, making it likely to react with another thiyl radical or thiolate to form the RS–SR species. On the other hand, for Au(111), the thiyl radical would form farther from the surface, reacting with the alkyl chains of neighboring molecules to form RS–R′ species. The mechanistic framework proposed here is very useful to explain the behavior of related systems., Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas

Au surfaces modified by Pd electrodeposits have been found to enhance the rates of nitrate electroreduction in acidic aqueous solutions containing Cd2+ over those of the bare Au substrate in the same media. Rather surprisingly, similar electrocatalytic effects were also observed for ensembles of Au and Pd nanoparticles supported on otherwise inert glassy carbon (GC) surfaces under the same conditions, which suggest that this phenomenon does not originate solely from specific interactions between the two metals. In fact, the overall electrocatalytic activity of GC surfaces decorated with either a fixed number of Au in one case, or a fixed number of Pd nanoparticles in the other, displayed much lower activity than GC surfaces covered with a mixture of half of each of them. This unique behavior may be explained by the ability of Pd to reduce NO2−, which is known to be the main reaction product of NO3− reduction on underpotential deposited Cd on Au. This work was supported by a grant from NSF, CHE-1412060.

Herein we investigate the effect of irreversibly adsorbed bismuth on polycrystalline platinum (Ptp) on the electrooxidation of glycerol in alkaline media by combining electrochemical, spectroscopic (in situ FTIR), and analytical (HPLC on line) techniques. We found that the activity of Ptp increases by about 5-fold when the optimal quantity of Bi ions is added to the solution. Besides, the adatom strongly impacts the reaction products by suppressing the pathways with C–C bond breaking, hindering the formation of CO (and other unknown intermediates) and enhancing the production of glycerate. Different from the results in acid media for Ptp-Bi systems where Bi blocks the oxidation pathway through the primary carbon, glycerate is the main product in alkaline media, and dihydroxyacetone is either produced in extremely low quantities or not produced. Besides, comparing our results with those in acid media, the peak current recorded at 1 mV·s–1 in this work was 1 order of magnitude higher. These results show the strong impact of the pH in the reaction rate and selectivity. Financial support from the Brazilian agencies: PSF and JLB thanks FAPESP (grants: 2016/01365-0) and Shell and the strategic importance of the support given by ANP (Brazil’s National Oil, Natural Gas and Biofuels Agency) through the R&D levy regulation. MBCS thanks PRP-FAEPEX and RAV and VYY thanks SAE-Unicamp for their scholarships. J.S-G. acknowledges financial support from VITC (Vicerrectorado de Investigación y Transferencia de Conocimiento) of the University of Alicante (UATALENTO16-02).

The development of new electrocatalysts with improved properties for the electrochemical reduction of CO2 is being the objective of innumerable contributions. In this contribution, the electrochemical reduction of CO2 to formate on novel carbon-supported antimony nanoparticles (Sb/C NPs) is studied. The carbon-supported Sb2O3/Sb nanoparticles were synthesised using a simple methodology at room temperature and characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The Sb2O3/Sb/C electrodes were prepared by air-brushed onto a carbon paper and were characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The Sb2O3/Sb/C electrodes were also electrochemically characterized by cyclic voltammetry and displayed a clear activity for CO2 electroreduction. To evaluate the properties of the electrodes for the reduction of CO2, electrolyses at different potentials were systematically conducted. Hydrogen and formate were the only products found. The faradic efficiency towards formate was found to be about 20%. This FE was in good agreement with previous finding obtained with comparable system. Interestingly, 24-hour tests were carried out to analyse the stability of the material under working conditions. The results indicate that Sb2O3/Sb-based electrodes display a remarkably better stability than other nanostructured electrocatalysts such as Sn or Bi. This work was supported by the MINECO, through the projects CTQ2016-76231-C2-2-R (AEI/FEDER, UE) and PID2019-108136RB-C32. Also, the invitation by the E3TECH Spanish Network of Excellence (CTQ2017-90659-REDT (MEIC/AEI)) is kindly acknowledged.

The knowledge about how CO occupies and detaches from specific surface sites on well-structured Pt surfaces provides outstanding information on both dynamics/mobility of COads and oxidation of this molecule under electrochemical conditions. This work reports how the potentiostatic growth of different coverage CO adlayers evolves with time on both cubic and octahedral Pt nanoparticles in acidic medium. Data suggest that during the growth of the CO adlayer, COads molecules slightly shift toward low coordination sites only on octahedral Pt nanoparticles, so that these undercoordinated sites are the first filled on octahedral Pt nanoparticles. Conversely, on cubic Pt nanoparticles, adsorbed CO behaves as an immobile species, and low coordinated sites as well as (100) terraces are apparently filled uniformly and simultaneously. However, once the adlayer is complete, irrespectively of whether the CO is oxidized in a single step or in a sequence of different potential steps, results suggest that COads behaves as an immobile species during its oxidation on both octahedral and cubic Pt nanoparticles. M. J. S. Farias is grateful to the CAPES/PNPD (Brazil) for the financial support. G. A. Camara acknowledges CNPq (grants no. 405695/2013-6 and 309176/2015-8) and FUNDECT (grants no. 23/200.583/2012). J. M. Feliu thanks the MINECO (Spain) project CTQ2016-76221-P. J.S.G. acknowledges financial support from VITC (Vicerrectorado de Investigación y Transferencia de Conocimiento) of the University of Alicante.

The development of electroanalytical methods for the detection and quantification of nucleotides in DNA offers vital implications in assessing the degree of oxidation or epigenetic modification in DNA. Unfortunately, the electrochemical response of oligonucleotides is strongly influenced by the size, composition and nucleic base sequence. In this article, an optimized analytical procedure for the enzymatically breakdown of the oligonucleotides to their corresponding nucleotides for the evaluation of the electrochemical response through the use of square wave voltammetry (SWV) is presented. Enzymatic digestion of oligonucleotides has been optimized in terms of buffer composition, digestion time, strategy for stopping the enzymatic reaction and filtration requirement for enzyme removal, and then compared to an established protocol. Under the optimized protocol SWV response of a number of untreated and enzymatically digested six-mer oligonucleotides, namely 5′-GGGGGG-3′, 5′-AAAAAA-3′, 5′-CGCGCG-3′ and 5′-AAACGC-3′ have been analysed, providing a higher sensitivity for the determination of guanosine and adenosine monophosphate species under digestion conditions with a more facile and cost effective procedure. The novel strategy for the enzymatically treated oligonucleotides in combination with the SWV response provides a proof of principle for feasible applications in the diagnosis of methylated guanosine in DNA as a potential biomarker due to its relation with cancer. This work has been also financially supported by the MINECO (Spain) through projects CTQ2013-48280-C3-3-R and CTQ2013-44083-P.

In this communication we report a voltammetric study of the adsorption–desorption of cytosine (C) and methylcytosine (mC) on well-defined gold (Au) electrodes. The voltammetric measurements clearly indicate that these processes are extremely sensitive to the Au surface structure and in particular to the presence of (111) surface domains. Interestingly, on Au(111) surfaces, a linear correlation between the C and mC concentrations (logarithm scale) and the peak potential of the main voltammetric feature is found. In addition, in the simultaneous presence of both molecules, mC governs the electrochemical response, which has allowed its accurate quantification in C-mC mixtures. In situ FTIR spectroscopic measurements have been carried out to deepen on this mC electrochemical sensitivity. This research may contribute to the future development of an electrochemical sensor for the determination of the degree of methylation in DNA. This work has been financially supported by the MINECO through projects CTQ2013-48280-C3-3-R, CTQ2013-44083-P and by the Generalitat Valenciana through project PROMETEOII/2014/013.

Different adatom modified shape-controlled Pt nanoparticles have been prepared and their electrocatalytic properties have been evaluated toward ethanol electrooxidation. Based on previous findings with Pt model surfaces, Sn, Rh, Ru and Pb adatoms have been selected as promising surface modifiers. The different adatoms have been gradually incorporated on the surface of the preferentially oriented (100) and (111) Pt nanoparticles under electrochemical conditions. The results obtained in 0.5 M H2SO4 indicated that, among the selected adatoms, Sn-modified nanoparticles displayed not only a significant shift to negative values on the onset potential of the ethanol oxidation, but also an important decrease on the hysteresis between the positive and negative sweeps. Interestingly, in chronoamperometic measurements at 0.6 V, the oxidation enhancement factors have been found to be dependent on the surface structure of the Pt nanoparticles. On the other hand, Ru and Pb-modified Pt nanoparticles only presented a rather small oxidation enhancement, whereas the activity of the Rh-modified Pt nanoparticles clearly diminished. In alkaline solutions, the oxidation mechanism changes, and the adsorption of Rh, Sn and Pb on the platinum surfaces just displays small catalytic effect at lower coverage for the potential onset in the voltammetric experiments. Ru adsorption does not present any positive effect over the reaction. This work has been financially supported by the Ministerio de Economía y Competitividad (project CTQ2013-44083-P) and Generalitat Valenciana (project PROMETEOII/2014/013).

Carbon-supported Pd nanocubes with the size of 30, 10 and 7 nm were prepared and their electrocatalytic activity towards the oxygen reduction reaction (ORR) in alkaline solution was studied. For comparison carbon-supported spherical Pd nanoparticles and commercial Pd/C catalyst were used. The catalysts were characterised by transmission electron microscopy, electro-oxidation of carbon monoxide and cyclic voltammetry and the ORR activity was evaluated using the rotating disk electrode method. The ORR on all studied Pd/C catalysts proceeded via four-electron pathway where the rate-limiting step was the transfer of the first electron to O2 molecule. The specific activity of Pd nanocubes was more than two times higher than that of spherical Pd nanoparticles and increased with increasing the particle size. This research was financially supported by institutional research funding (IUT20-16) by the Estonian Ministry of Education and Research and by the Estonian Research Council (Grant No. 9323).

The electrochemical conversion of CO2 is gaining increasing attention because it could be considered as an appealing strategy for making value-added products at mild conditions from CO2 captured. In this work, we report a process for the electrocatalytic reduction of CO2 to formate (HCOO-) operating in a continuous way, employing a single pass of the reactants through the electrochemical reactor and using Bi carbon supported nanoparticles in the form of a membrane electrode assembly composed by a Gas Diffusion Electrode, a current collector and a cationic exchange membrane. This contribution presents the best trade-off between HCOO- concentration, Faradaic Efficiency and energy consumption in the literature. We also show noteworthy values of energy consumption required of only 180 kWh·kmol-1 of HCOO-, lower than previous approaches, working at current densities that allow achieving formate concentration higher than 300 g·L-1 and simultaneously, a Faradaic Efficiency close to 90%. The results here displayed make the electrochemical approach closer for future implementation at the industrial scale. The authors of this work would like to acknowledge to the financial support from the MINECO, through the projects CTQ2016-76231-C2-1-R and CTQ2016-76231-C2-2-R (AEI/FEDER, UE). J.S.G acknowledges financial support from VITC (Vicerrectorado de Investigación y Transferencia de Conocimiento) of the University of Alicante (UTALENTO16-02). G.D.S, M.A.G and A.I filed a patent application on the experimental reaction system discussed here.

Electrocatalytic reduction of CO2 has been taken into consideration as a fascinating option to store energy from intermittent renewable sources in the form of chemical value-added products. Among the different value-added products, formic acid or formate is particularly attractive since it can be used as a fuel for low-temperature fuel-cells and as a renewable hydrogen carrier. Very recently, a rapidly increasing number of studies have revealed Bi as a promising electrocatalytic material for the CO2 electroreduction to formate, but the performance of Bi electrodes operating in a continuous mode and high current density (j) has been hardly investigated yet. Thus, this work aims at studying the CO2 electroreduction to formate working in a continuous mode in a filter-press-reactor at a j up to 300 mA·cm−2 using Bi electrodes. Bismuth Gas Diffusion Electrodes (Bi-GDEs) were fabricated from carbon-supported Bismuth-nanoparticles. The influence of j and the electrolyte flow/area ratio in the performance of the Bi-GDEs towards formate were evaluated. Working at j of 300 mA·cm−2, a concentration of 5.2 g formate·L−1 with a faradaic efficiency (FE) and rate of 70% and 11 mmol·m−2·s−1, respectively were achieved. Lowering the j to 90 mA·cm−2, formate concentrations of up to 7.5 g·L−1 could be obtained with an excellent FE of 90%. Interestingly, the highest concentration of formate obtained was 18 g·L−1, but at expenses of an important decrease in FE. Although the results of this study are interesting and promising, further research is required to increase formate concentration for a future implementation at industrial scale. The authors of this work would like to show their gratitude to the financial support from the MINECO, through the projects CTQ2016-76231-C2-1-R and CTQ2016-76231-C2-2-R (AEI/FEDER, UE). Jose Solla-Gullón also acknowledges the financial support from VITC of the University of Alicante (UTALENTO16-02).

The formic acid oxidation reaction has been studied on Pt(111), Pt(100) and Pt nanoparticles with preferential (111) surface structure in 0.1 M HClO4 in the presence of different concentrations of acetonitrile. An electrocatalytic enhancement towards the formic acid oxidation has been observed under these conditions, and it is proposed that this enhancement is due to two different effects of the adsorbed acetonitrile species: a third-body effect which hinders the formation of CO and a promoting effect of the direct oxidation of formic acid. This promoting effect is structure sensitive. The different enhancement between Pt(111) and Pt(100) indicates that the ratio of free Pt sites and sites occupied by adsorbed acetonitrile is important in order to have the better electrocatalytic activity. On-line mass spectrometry (OLEMS) measurements confirmed the preference for the direct oxidation of formic acid to CO2, which is almost complete below 0.3 V vs. RHE for Pt(111). Finally, chronoamperometric studies confirmed the lower poisoning rate in the presence of acetonitrile but they also pointed out a competition of formed CO for the Pt sites occupied by acetonitrile species. This work constitutes an example of electrocatalytic enhancement by using an organic molecule for surface modification, which is not as common as using metallic adlayers. This work has been financially supported by the MINECO-FEDER (Spain) through project CTQ2016-76221-P. V. B-M thankfully acknowledges to MINECO the award of a predoctoral grant (BES-2014-068176, project CTQ2013-44803-P) and a student stay grant (EEBB-I-16-11656). S-G. acknowledges financial support from Vicerrectorado de Investigación y Transferencia de Conocimiento of the University of Alicante (UATALENTO16-02).

Coherent imaging in the Bragg geometry of nanoparticles inside an electrochemical cell is presented., Nanoparticles are essential electrocatalysts in chemical production, water treatment and energy conversion, but engineering efficient and specific catalysts requires understanding complex structure–reactivity relations. Recent experiments have shown that Bragg coherent diffraction imaging might be a powerful tool in this regard. The technique provides three-dimensional lattice strain fields from which surface reactivity maps can be inferred. However, all experiments published so far have investigated particles an order of magnitude larger than those used in practical applications. Studying smaller particles quickly becomes demanding as the diffracted intensity falls. Here, in situ nanodiffraction data from 60 nm Au nanoparticles under electrochemical control collected at the hard X-ray nanoprobe beamline of MAX IV, NanoMAX, are presented. Two-dimensional image reconstructions of these particles are produced, and it is estimated that NanoMAX, which is now open for general users, has the requisites for three-dimensional imaging of particles of a size relevant for catalytic applications. This represents the first demonstration of coherent X-ray diffraction experiments performed at a diffraction-limited storage ring, and illustrates the importance of these new sources for experiments where coherence properties become crucial.

The number of publications devoted to studying electrochemical reactions in room temperature ionic liquids (RTILs) is constantly growing, but very few of them have been devoted to defining proper experimental conditions to obtain reproducible electrochemical results. In this work, we demonstrate that the combination of a proper RTIL purification treatment and a filtered Ar gas stream allow us to obtain featureless voltammograms in [C4mim][BF4], [C4mim][NTf2], and [C4m2im][NTf2], which otherwise present signals associated with different types of impurities such as water and some minor electroactive impurities acquired during the RTIL synthesis process. Moreover, we demonstrate that bubbling Ar, or another inert gas, through the electrolyte in order to purge O2 dissolved in RTILs is one of the major sources of water and O2 impurities incorporated in RTILs within the electrochemical cell. To overcome this source of water uptake, we have incorporated a gas stream purification filter before the gas reaches the RTIL in the electrochemical cell. To illustrate the effect of these impurities in relevant electrocatalytic studies, we study the electrocatalytic reduction of CO2 on Pt nanoparticles and the key role of an appropiate filter when the CO2 gas stream is bubbled within imidazolium based RTILs. Our cyclic voltammetric studies point out that CO2 electroreduction on Pt nanoparticles only presents activity in [C4mim][NTf2] and [C4m2im][NTf2], thus suggesting that the C-2 position on the imidazolium ring is not the key position in CO2 electrochemical reduction. In contrast, the same Pt nanoparticles are inactive towards CO2 electroreduction in [C4mim][BF4], which is a more hydrophilic RTIL. The authors acknowledge financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) (projects CTQ2013-48280-C3-3-R and CTQ2016-76231-C2-2-R) (AEI/FEDER, UE) and from the CNRS (projet Défi Instrumentation aux limites 2015). J. S.-G. acknowledges financial support from VITC (Vicerrectorado de Investigación y Transferencia de Conocimiento) of the University of Alicante (UATALENTO16-02). C. M. S.-S. acknowledges financial support from the University of Alicante, visiting researcher grant INV16-15.

The use of adatom decorated shape-controlled metal nanoparticles in electrocatalysis, and particularly for energy conversion reactions, has made important contributions to the development of better electrocatalysts. In this short review, we highlight some of the most relevant findings and discuss about future challenges. J.S-G and P.S.F. acknowledges financial support from FAPESP (Process numbers 2017/09780-0 and 2016/01365-0). J.S-G. also acknowledges financial support from VITC (Vicerrectorado de Investigación y Transferencia de Conocimiento) of the University of Alicante (UATALENTO16-02). M.B.C.S acknowledges CAPES for his fellowship.

Pd nanocrystals were produced with uniform truncated-cube shape and a narrow size distribution, yielding controlled surface area fractions from low Miller index ({100}, {110}, {111}) crystalline facets. Details on the structure and morphology of the nanocrystals were obtained by combining X-ray powder diffraction line profile analysis, high-resolution transmission electron microscopy and surface electrochemistry based on Cu underpotential deposition. ML acknowledges support from the Italian government (Ministero dell’Istruzione, dell’Università e della Ricerca) through the project FIRB Futuro in Ricerca RBFR10CWDA. JMF acknowledges financial support from the MINECO (Spain) project CTQ2013-44083-P and Generalitat Valenciana project PROMETEOII/2014/013.

The ethanol oxidation reaction in 0.1 M NaOH on Pt nanoparticles with different shapes and loadings was investigated using electrochemical and spectroscopic techniques. The surface structure effect on this reaction was studied using well-characterized platinum nanoparticles. Regardless of the type of Pt nanoparticles used, results show that acetate is the main product with negligible CO2 formation. From the different samples used, the nanoparticles with a large amount (111) of ordered domains have higher peak currents and a higher onset potential, in agreement with previous works with single crystal electrodes. In addition, spherical platinum nanoparticles supported on carbon with different loadings were used for studying possible diffusional problems of ethanol to the catalyst surface. The activity in these samples diminishes with the increase of Pt loading, due to diffusional problems of ethanol throughout the whole Pt nanoparticle layer, being the internal part of the catalyst layer inactive for the oxidation. To avoid this problem and prepare more dispersed nanoparticle catalyst layers, deposits were dried while the carbon support was rotated to favor the dispersion of the layer around the support. The improvement in the electrocatalytic activity for ethanol oxidation confirms the better performance of this procedure for depositing and drying. This work has been financially supported by the Ministerio de Economía y Competitividad and Generalitat Valenciana through projects CTQ2013-44083-P and PROMETEOII/2014/013, respectively.

The demand for power sources alternative to fossil fuels makes urgent the development of more efficient electrocatalysts for fuel cells applications and the maximization of the performances of the existent ones. This work reports, for the first time, the use of carbon-supported shape-controlled Pt nanoparticles as anode catalysts in direct ethanol fuel cells. By using cubic Pt nanoparticles, on which (100) surface sites are predominant, the performance of the fuel cell can be increased from 14 to 24 mW per mg of Pt when compared with cuboctahedral nanoparticles. Moreover, the open circuit potential shifts about 50 mV toward more positive potentials. In comparison with commercially available Pt catalysts, the performance for the (100) preferentially oriented nanoparticles is about three times higher. The reported results evidence that, from an applied point of view, the effect of the surface structure/shape of the electrocatalysts can be also considered to improve the performance of real fuel cell systems. Keywords: Direct ethanol fuel cells, Shape controlled nanoparticles, Electrocatalysis

The surface orientation effect on the oxidation of small organic molecules such as methanol, formaldehyde, ethanol, and glycerol has been studied on Au nanoparticles in alkaline medium. Two sets of Au nanoparticles enriched in (100) and (111) facets were synthetized by using colloidal methods in presence of cetyltrimethylammonium bromide. The nanoparticles were physically characterized by using TEM and XRD and electrochemically characterized by using Pb underpotential deposition as a surface-structure probe. It is reported that, although methanol oxidation was similar in both types of nanoparticles, the oxidation of formaldehyde presented a clear surface orientation effect. For this reaction, nanoparticles with (111) preferential orientation presented higher current densities at low potentials, whereas Au(100) nanoparticles exhibited higher activity at potentials more positive than 1.0 V versus RHE. On the other hand, for glycerol and ethanol oxidations, the onset of the reaction was similar in both types of particles, although Au(111) nanoparticles showed higher current densities than the Au(100) ones. P.R. acknowledges financial support from the Netherlands Organization for Scientific Research (NWO) through a VENI grant and the University of Birmingham through a Birmingham Fellowship.

The electrochemical valorisation of captured CO2 is an attractive option to obtain value-added products, and at the same time, to chemically store energy from intermittent renewable sources. Among the different products, formic acid/formate is particularly interesting since it is one of the most promising materials for hydrogen storage and candidate fuel for low-temperature fuel cells. In this work, a process for CO2 electroreduction to formate is studied on a continuous filter-press cell using an innovative electrode: Sn Catalyst Coated Membrane Electrodes (Sn-CCMEs) - comparing with previous approaches based on Sn Gas Diffusion Electrodes (Sn-GDEs), using the same synthesised tin nanoparticles (Sn NPs) and operating conditions. The Sn-CCME is prepared by depositing Sn NPs directly over a Nafion 117 membrane, and it allows working with a gaseous CO2 flow humidified with water as the input of the electrochemical cell, avoiding the use of the liquid catholyte. Sn-CCME operates at lower current densities (45 mA cm-2) than previous Sn-GDEs (200 mA cm-2), which resulted in lower rates of formate production. However, the proposed Sn-CCME, allowed achieving even higher formate concentrations with an energy consumption 50% lower than with the Sn-GDEs. The influence of key variables such as temperature and water input flow on the performance of the process using Sn-CCMEs was also analysed in a controlled experimental set-up specifically designed and built for this goal. Increasing the temperature of the gaseous stream did not improve the performance. The best results were obtained at ambient conditions of temperature (20 °C) and with the amount of water in the CO2 stream at 0.5 g h-1, giving the highest formate concentration (19.2 g L-1) with a Faradaic efficiency close to 50% and an energy consumption of 244 kW h kmol-1. More research is still required to further improve CCME configuration in order to increase formate rate and efficiency without increasing energy consumption. This work was conducted under the framework of the Spanish Ministry of Economy, Industry and Competitiveness (MINECO), projects CTQ2016-76231-C2-1-R (AEI/FEDER, UE) and CTQ2016-76231-C2-2-R (AEI/FEDER, UE). JSG acknowledges financial support from VITC (Vicerrectorado de Investigación y Transferencia de Conocimiento) of the University of Alicante (UTALENTO16-02).

The development of green and scalable syntheses for the preparation of size- and shape-controlled metal nanocrystals is of high interest in many areas, including catalysis, electrocatalysis, nanomedicine, and electronics. In this work, a new synthetic approach based on the synergistic action of physical parameters and reagents produces size-tunable octahedral Pt nanocrystals, without the use of catalyst-poisoning reagents and/or difficult-to-remove coatings. The synthesis requires only sodium citrate, ascorbic acid, and fine control of the reduction rate in aqueous environment. Pt octahedral nanocrystals with particle size as low as 7 nm and highly developed {111} facets have been achieved, as demonstrated by Transmission Electron Microscopy, X-ray Diffraction, and electrochemical methods. The absence of sticky molecules together with the high quality of the surface renders these nanocrystals ideal candidates in electrocatalysis. Notably, 7 nm bismuth-decorated octahedral nanocrystals exhibit superior performance for the electro-oxidation of formic acid in terms of both specific and mass activities. JMF and VM acknowledge financial support from MINECO (projects CTQ2016-76221-P and CTQ2016-76231-C2-2-R (AEI/FEDER, UE)). JSG acknowledges financial support from VITC (Vicerrectorado de Investigación y Transferencia de Conocimiento) of the University of Alicante (UATALENTO16-02).

Nanocatalyst performance towards the ethanol oxidation reaction (EOR) for fuel cell applications can be enhanced by exploiting the benefits of structural and compositional sensitivity and control. We describe the synthesis and characterization of cubic Pt-Sn alloyed nanoparticles consisting of (100) faceted Pt-Sn nanoparticles with a core-shell structure, with a Pt-rich core and a Sn-rich shell. Stability tests indicated that this catalyst preserves its morphology and remains well-dispersed on the carbon support after 5,000 potential cycles, while a cubic (pure) Pt catalyst exhibited severe agglomeration of the nanoparticles after the same stability testing protocol. Analysis of the elemental distribution in the nanoparticles by STEM-EELS indicated that Sn dissolves from the outer part of the shell after potential cycling, forming a ~0.5 nm Pt skin. Finally, the activity of this bimetallic core-shell nanostructured electrocatalyst towards the EOR was investigated, exhibiting currents about three times higher than those of unshaped Pt-Sn nanoparticles and six times higher than Pt nanocubes., This work has been supported by Fundación Cajacanarias (project BIOGRAF), the Ministry of Economy and Competitiveness (MINECO) through the projects CTQ2011-28913-C02-02 and ENE2014-52158-C2-2-R (co-funded by FEDER) and the. The authors acknowledge the SEGAI services of Universidad de La Laguna for important technical assistance and R.R also thanks the funding received from MINECO (EEBB-I-16-11762) to carry out a predoctoral stay in a foreign R&D center. E.P. acknowledges support from an electron microscopy facilities supported by the NSF MRSEC program (DMR 1120296) and an NSF MRI grant (DMR 1429155).J.S.G. acknowledges financial support from VITC (Vicerrectorado de Investigación y Transferencia de Conocimiento) of the University of Alicante.

The application of shape-controlled metal nanoparticles is profoundly impacting the field of electrocatalysis. On the one hand, their use has remarkably enhanced the electrocatalytic activity of many different reactions of interest. On the other hand, their usage is deeply contributing to a correct understanding of the correlations between shape/surface structure and electrochemical reactivity at the nanoscale. However, from the point of view of an electrochemist, there are a number of questions that must be fully satisfied before the evaluation of the shaped metal nanoparticles as electrocatalysts including (i) surface cleaning, (ii) surface structure characterization, and (iii) correlations between particle shape and surface structure. In this chapter, we will cover all these aspects. Initially, we will collect and discuss about the different practical protocols and procedures for obtaining clean shaped metal nanoparticles. This is an indispensable requirement for the establishment of correct correlations between shape/surface structure and electrochemical reactivity. Next, we will also report how some easy-to-do electrochemical experiments including their subsequent analyses can enormously contribute to a detailed characterization of the surface structure of the shaped metal nanoparticles. At this point, we will remark that the key point determining the resulting electrocatalytic activity is the surface structure of the nanoparticles (obviously, the atomic composition is also extremely relevant) but not the particle shape. Finally, we will summarize some of the most significant advances/results on the use of these shaped metal nanoparticles in electrocatalysis covering a wide range of electrocatalytic reactions including fuel cell-related reactions (electrooxidation of formic acid, methanol and ethanol and oxygen reduction) and also CO2 electroreduction. Graphical Abstract

A collection of shape-controlled Pt nanoparticles has been prepared using two different and previously described methodologies, both using oleylamine/oleic acid as capping material/solvent. A new decontamination protocol is presented to effectively clean the surface of the different nanoparticles thus allowing a full exposure of their surface area and consequently to make the most of their surface structure dependent reactivity. Subsequently, the clean shape-controlled Pt nanoparticles have been electrochemically characterized and their electrocatalytic properties evaluated towards some surface structure reactions of interest. The results indicate that the full characterization of the surface structure cannot be done exclusively by the available microscopy techniques, since it is very difficult to determine the presence of surface defects. Additional surface characterization probes, such as those provided by electrochemical surface sensitive reactions, have been used to assess the surface structure of the samples. This work has been financially supported by the MICINN (Feder) of Spain and Generalitat Valencia through Projects CTQ2013-44083-P and PROMETEOII/2014/013, respectively.

The electrochemical kinetic behavior of the oxygen reduction reaction (ORR) on PdPt alloy nanocubes of various compositions is investigated in 0.1 M KOH and 0.1 M HClO4 solutions, adopting the rotating disk electrode (RDE) configuration. The PdPt nanocubes are prepared in the presence of polyvinylpyrrolidone and identified by using transmission electron microscopy (TEM). TEM images reveal that the PdPt alloy nanoparticles have a preferential cubic shape and the average particle size is approximately 8–10 nm. CO-stripping and cyclic voltammetry (CV) experiments are used for electrochemical cleaning and characterization of metal nanoparticles. The CV responses indicate alloy formation. In acidic media, Pd36Pt64 shows the highest specific activity (SA) for the ORR from the alloyed catalysts studied, but this activity is similar to that found with Pt and Pd nanocubes. However, in alkaline solution, the SA value for Pd72Pt28 is about two times higher than that of Pd and Pt nanocubes. The mechanistic pathway of O2 reduction on PdPt alloy nanocubes is analogous to that of pure Pd and Pt catalysts and the ORR proceeds via a 4-electron pathway in both electrolyte solutions. This research was financially supported by institutional research funding (IUT20-16) of the Estonian Ministry of Education and Research and by the Estonian Research Council (Grant No. 9323). This research was also supported by the EU through the European Regional Development Fund (TK141 “Advanced materials and high-technology devices for energy recuperation systems”). K.J. thanks the Archimedes Foundation for scholarship. J.M.F. acknowledges financial support from MINECO (Spain), project CTQ2016-76221-P. J.S.G. acknowledges financial support from VITC (Vicerrectorado de Investigación y Transferencia de Conocimiento) of the University of Alicante.

To understand how the CO oxidation reaction proceeds on nanoparticles, which have complex surface structures, the behavior of the nanoparticles has to be related to that of single crystal electrodes with a well-defined surface structure. However, the direct extrapolation of the results is not possible because significant differences in the behavior between both type of surfaces are observed. In single crystal electrodes in both acidic and alkaline media, the reaction initiates on defects on the CO adlayer. These defects can be already present on the surface, as surface defects or steps, or generated during the formation of the CO adlayer. In the case of steps, the oxidation starts on the lower part of the step. The only difference between the reaction behavior between acidic and alkaline solutions is the lower mobility of the CO in alkaline solutions, which generates adlayers with higher number of defects and give rise to multiple stripping peaks in stepped surfaces. Using these results, the differences of the behavior between single crystal electrodes and nanoparticles can be rationalized. In spite of the fact that nanoparticles have small ordered domains, the presence of sites in which the reaction is initiated, equivalent to the site in the lower part of the step, is almost negligible, and thus, the oxidation reaction takes place at higher potential values than in stepped surfaces with similar domain size. Also the effect of nanoparticle agglomeration in the oxidation has been rationalized. This work has been financially supported by the MINECO-FEDER (projects CTQ 2013-44083-P and CTQ2013-48280-C3-3-R) and Generalitat Valenciana (project PROMETEO/2014/013). M.J.S. Farias acknowledges financial support from the CAPES – Brasil (PNPD).