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An active and stable hydrogen evolution electrocatalyst composed of MoO2 surface nanorod arrays was prepared using high-temperature reductive annealing. Electrodes with an area of 78.5 cm2 were evaluated in a three-cell AEM electrolyser stack.

This study reports the preparation, characterization, and electrocatalytic properties of palladium-based catalysts containing ceria (CeO2) on carbon black (CB) and onion-like carbon (OLC) supports. The electrocatalysts (Pd-CeO2/CB and Pd-CeO2/OLC) exhibit a large specific surface area, pore volume, and small particle size, as well as enhanced interfacial interaction and synergy among Pd, CeO2, and OLC in Pd-CeO2/OLC that are valuable for improved electrocatalysis. The presence of CeO2 in Pd-CeO2/OLC induces ca. 7% defects and modifies the electronic structure of the Pd/OLC interface, significantly improving the electrical conductivity due to enhanced charge redistribution, corroborated by density functional theory (DFT) calculations. Pd-CeO2/OLC displays the lowest adsorption energies (H*, OH*, and OOH*) among the series. For the hydrogen oxidation reaction (HOR), Pd-CeO2/OLC delivers significantly enhanced HOR (mass-specific) activities of 4.2 (8.1), 13.2 (29.6), and 15 (78.5) times more than Pd-CeO2/CB, Pd/OLC, and Pd/CB, respectively, with the best diffusion coefficient (D) and heterogeneous rate constant (k). Pd-CeO2/OLC also displays less degradation during accelerated durability testing. In an anion-exchange-membrane fuel cell (AEMFC) with H2 fuel, Pd-CeO2/OLC achieved the highest peak power density of 1.0 W cm-2 at 3.0 A cm-2 as compared to Pd-CeO2/CB (0.9 W cm-2 at 2.2 A cm-2), Pd/OLC (0.6 W cm-2 at 1.7 A cm-2), and Pd/CB (0.05 W cm-2 at 0.1 A cm-2). These results indicate that Pd-CeO2/OLC promises to serve as a high-performing and durable anode material for AEMFCs.

Recently, several researchers have claimed the existence of superior catalytic activity associated with topological materials belonging to the class of Dirac/Weyl semimetals, owing to the high electron conductivity and charge carrier mobility in these topological materials. By means of X-ray photoelectron spectroscopy, electrocatalytic tests, and density functional theory, we have investigated the chemical reactivity (chemisorption of ambient gases), ambient stability, and catalytic properties of PdSn4, a topological semimetal showing Dirac node arcs. We find a Tafel slope of 83 mV in the hydrogen evolution reaction (HER) dec-1with an overpotential of 50 mV, with performances resembling those of pure Pd, regardless of its limited amount in the alloy, with a subsequent reduction in the cost of raw materials by ∼80%. Remarkably, the PdSn4-based electrode shows superior robustness to CO compared to pure Pd and Pt and high stability in water media, although the PdSn4surface is prone to oxidation with the formation of a sub-nanometric SnO2skin. Moreover, we also assessed the significance of the role of topological electronic states in the observed catalytic properties. Actually, the peculiar atomic structure of oxidized PdSn4enables the migration of hydrogen atoms through the Sn-O layer with a barrier comparable with the energy cost of the Heyrovsky step of HER over Pt(111) in acidic media (0.1 eV). On the other hand, the topological properties play a minor role, if existing, contrarily to the recent reports overestimating their contribution in catalytic properties. © 2021 The Authors. Published by American Chemical Society D.W.B. acknowledges the support from the Ministry of Science and Higher Education of the Russian Federation (through the basic part of the government mandate, project no. FEUZ-2020-0060 and Jiangsu Innovative and Entrepreneurial Talents Project). A.M., J.F., and F.V. acknowledge the Italian Ministry of University and Research MUR by the PRIN 2017 (no. 2017YH9MRK) and MISE FISR 2019 AMPERE (FISR2019_01294) projects for the financial support.

The performances of the core-shell nano-electrocatalysts (FeCo@Fe@Pd/CNT-OH and their monometallic Pd counterparts (Pd/CNT-OH) on carbon nanotubes in passive and active direct methanol fuel cells (DMFCs) and direct ethanol fuel cells (DEFCs) have been studied. The direct alcohol alkaline fuel cell (DAAFCs) performances of the two nanocatalysts studied revealed the outstanding performances of the core shell, FeCo@Fe@Pd catalysts over the single Pd metal on the same substrates. A fourfold increase in power density value was observed in the DEFC while a threefold increase was seen in the DMFC while operating both passive DAAFCs at moderate temperatures using the core shell nanocatalysts. The core-shell-modified electrode also gave an exceptional activity of over 50% columbic efficiency in comparison with its Pd counterpart in the passive DEFC. Density functional theory calculations carried out to further comprehend the electrocatalytic oxidation of the nanocatalysts towards both methanol and ethanol fuels corroborated the experimental findings. An increase in the readily available electrons of the partially filled d-orbitals was found to be involved in the catalytic reactions on the surface of the FeCo@Fe@Pd/CNT-OH core shell catalysts as opposed to those of the p-orbitals of Pd/CNT-OH, thus enhancing its catalytic activities in both DAAFCs.

In anion exchange membrane fuel cells, catalytic reactions occur at a well-defined three-phase interface, wherein conventional heterogeneous catalyst layer structures exacerbate problems such as low catalyst utilization and limited mass transfer. We developed a structural engineering strategy to immobilize a molecular catalyst tetrakis(4-methoxyphenyl)porphyrin cobalt(II) (TMPPCo) on the side chains of an ionomer (polyfluorene, PF) to obtain a composite material (PF-TMPPCo), thereby achieving a homogeneous catalysis environment inside ion flow channels, with greatly improved mass transfer and turnover frequency due to 100% utilization of the catalyst molecules. The unique brand-new structure of the homogeneous catalysis system comprising interconnected nanoreactors exhibits advantages of low overpotential and high fuel cell power density. This strategy of reshaping of the catalyst layer structure may serve as a new platform for applications of many molecular catalysts in fuel cells.

The dinuclear Ru diazadiene olefin complex, [Ru2(OTf)(μ-H)(Me2dad)(dbcot)2], is an active catalyst for hydrogen evolution in a Polymer Exchange Membrane (PEM) water electrolyser. When supported on high surface area carbon black and at 80 °C, [Ru2(OTf)(μ-H)(Me2dad)(dbcot)2]@C evolves hydrogen at the cathode of a PEM electrolysis cell (400 mA cm−2, 1.9 V). A remarkable turn over frequency (TOF) of 7800 molH2 molcatalyst−1 h−1 is maintained over 7 days of operation. A series of model reactions in homogeneous media and in electrochemical half cells, combined with DFT calculations, are used to rationalize the hydrogen evolution mechanism promoted by [Ru2(OTf)(μ-H)(Me2dad)(dbcot)2]., Chemical Science, 13 (13), ISSN:2041-6520, ISSN:2041-6539

Nicked-based metal–organic framework-derived carbon (Ni/MOFDC) and its acid-treated counterpart (AT-Ni/MOFDC) have been prepared as supports for palladium nanoparticle electrocatalysts (Pd/Ni/MOFDC...

The electrochemical reforming of ethanol to H2 is achieved at 150 °C in an autoclave electrochemical cell that allows the safe pressurization of the H2 produced as no O2 is evolved. The alkaline conditions are very aggressive to catalysts including noble metals like Pt and Pd. We report a highly active ethanol oxidation catalyst (PdCoNifoam) composed of Pd nanoparticles supported on nanostructured Co oxide structures grown on nickel foam. Treatment with phosphorous vapors at high temperature yields a thin coating of phosphate that confers enhanced stability to the electrode operating in an electrolysis cell at 150 °C. A combination of scanning electron microscopy (energy dispersive X-ray spectroscopy) and X-ray photoelectron spectroscopy reveal a 3D nano-flake surface with an external layer of phosphates that prevents Pd dissolution. The PdCoP@Nifoam catalyst was successfully used for ethanol electrochemical reforming at 150 °C with self-pressurization of the H2 produced by the electrochemical reaction.

By means of surface-science experiments, electrochemical tests and density functional theory, we unveil the mechanisms ruling the catalytic activity of PtSn4. Specifically, through an investigation of the surface chemical reactivity toward CO, H2O, and O2 molecules at room temperature and, moreover, of surface stability in air, we show that the catalytic activity of PtSn4 is determined by the atomic tin layer constituting its surface termination. The PtSn4 surface is not affected by CO poisoning, although it evolves into a tin-oxide skin in the ambient atmosphere. We demonstrate that the hydrogen evolution reaction on PtSn4 can be modelled by the combination of two steps, i.e. Volmer and Tafel reactions. Surprisingly, surface oxidation induces a reduction of the energy barrier for the Tafel reaction, so that oxidized PtSn4 behaves similarly to Pt(111), in spite of the reduced amount of Pt in the alloy and without available over-surface Pt sites. Correspondingly, we observe in electrochemical experiments a Tafel slope of 86 mV dec−1 and an onset potential similar to that of pure Pt. However, PtSn4 contains only 29% wt of Pt, with a reduction of the economic cost by 70%. Our results indicate PtSn4 as a promising novel material for electrocatalytic reactions, whose performance could be further tuned by surface treatments.

Since its first reported exfoliation in 2014, the interest in 2D black phosphorus (2D BP) and its chemical functionalization has grown dramatically [1], though a satisfactory structural description of the modified materials is seldom achieved. Herein, the functionalization of 2D BP starting from molecular Pd precursors is presented, leading either to supported Pd NPs (Pd/BP) or to interlayer Pd-Pd discrete units (Pd2/BP). An in-depth solid-state characterization of the new materials was carried out by means of XPS, HAADF-STEM, XRD, NMR MAS and XAS. Remarkably, XAS analysis, backed up by DFT modelling, was crucial in revealing the existence of Pd2 moieties stacked amidst BP layers in Pd2/BP. The potential application of these heterogeneous systems as catalysts was demonstrated in distinct processes, namely the selective hydrogenation of chloronitrobenzene to chloroaniline and the hydrogen evolution reaction (HER) from acidic medium.

The development of low-cost and sustainable hydrogen production is of primary importance for a future transition to sustainable energy. In this work, the selective and simultaneous production of pure hydrogen and chemicals from renewable alcohols is achieved using an anion exchange membrane electrolysis cell (electrochemical reforming) employing a nanostructured Pd-CeO2/C anode. The catalyst exhibits high activity for alcohol electrooxidation (e.g. 474 mA cm−2 with EtOH at 60 °C) and the electrolysis cell produces high volumes of hydrogen (1.73 l min−1 m−2) at low electrical energy input (Ecost = 6 kWh kgHjavax.xml.bind.JAXBElement@16146147−1 with formate as substrate). A complete analysis of the alcohol oxidation products from several alcohols (methanol, ethanol, 1,2-propandiol, ethylene glycol, glycerol and 1,4-butanediol) shows high selectivity in the formation of valuable chemicals such as acetate from ethanol (100%) and lactate from 1,2-propandiol (84%). Importantly for industrial application, in batch experiments the Pd-CeO2/C catalyst achieves conversion efficiencies above 80% for both formate and methanol, and 95% for ethanol.

Hydrogen has the largest energy density of all fuels and is considered the more suitable energy source (properly H2 is an energy vector) for matching a clean and carbon neutral future energetic scenario. This rather old technology was theorized almost 50 years ago but still doesn't have a widespread application due to severe limitations. The high cost and the poor sustainability for large scale application of electrochemical devices for hydrogen production and conversion to electricity are the main limitations. In fact, proton exchange membrane electrolyzers (PEMs) and fuel cells (PEMFCs) employ catalysts based on high amounts of rare noble metals, such as Pt, Ir, Ru and Pd. In addition, proton exchange membranes, such as the DuPont Nafion®, are very expensive materials. The reduction of precious metal loadings to negligible amounts keeping constant catalyst activity is a possible route for making fuel cells and electrolyzers sustainable devices. Traditional electrocatalysts are based on metal nanoparticles dispersed on conductive supports where only the particles surface atoms are involved in electrocatalysis. Replacing nanoparticles with metal complexes is a way for making accessible each metal center of the catalyst. A molecular catalyst offers other advantages with respect to nanosized materials, such as control of the selectivity of the oxidation reaction occurring in direct fuel cells fed with liquid and renewable fuels such as alcohols and formic acid. So direct fuel cells can convert a biomass-derived fuel not only into electricity but also into high purity chemicals. A second route to make fuel cells and electrolyzers sustainable devices is the replacement of proton exchange membranes with anion exchange membranes (AEMs) because in alkaline environment several nanostructured catalysts based on cheap metals can be used (in acidic environment most of the transition metals would be subject to corrosion phenomena). Thanks to the development over the last few years of high efficiency and stable alkaline membranes, we have developed anodic and cathodic nanostructured catalysts based on cheap metals like iron and nickel which are assembled together in alkaline fuel cells and eletrolyzers able to reach an activity close to the state of the art PEM based devices. As example an iron phthalocyanine cathode based H2/O2 fed fuel cell set up in our laboratory delivered a remarkable power density of 1 W cm-2.

The chemical functionalization of 2D exfoliated black phosphorus (2D BP) continues to attract great interest, although a satisfactory structural characterization of the functionalized material has seldom been achieved. Herein, we provide the first complete structural characterization of 2D BP functionalized with rare discrete Pd2 units, obtained through a mild decomposition of the organometallic dimeric precursor [Pd(?3-C3H5)Cl]2. A multitechnique approach, including HAADF-STEM, solid-state NMR, XPS, and XAS, was used to study in detail the morphology of the palladated nanosheets (Pd2/BP) and to unravel the coordination of Pd2 units to phosphorus atoms of 2D BP. In particular, XAS, backed up by DFT modeling, revealed the existence of unprecedented interlayer Pd-Pd units, sandwiched between stacked BP layers. The preliminary application of Pd2/BP as a catalyst for the hydrogen evolution reaction (HER) in acidic medium highlighted an activity increase due to the presence of Pd2 units.

The hydrogen economy is becoming more feasible in recent years due to technological progresses in materials development. Such improvements have allowed a reduction in manufactory cost from year to year, making hydrogen competitive with the solutions currently available on the market. To this regard, the best way to produce H2 is by water electrolysis, that is one of the most abundant and renewable sources of hydrogen present in nature. Unfortunately, some problems remain due to the use of critical raw materials employed for the fabrication of the catalysts, like Platinum Group Metal (PGM) and the membrane stability and permeability. In order to make these technologies available to a large market, many efforts have been made to limit or eliminate precious metals from the catalysts. Here we report PGM free catalysts for anion exchange membrane electrolyzer based on Nickel-Molybdenum alloys and iron oxide-hydroxide: MoNi4:MoOx-3/Nifoam for the cathode and Fe-MoNi4:MoOx-3/Nifoam for the anode. These materials have some interesting advantages; firstly a facile hydrothermal synthesis, this procedure requires only the metal salts and water, representing also a "green" alternative with respect other pathways, once the mixed oxide are grown on the Nifoam surface , thermal annealing under reducing atmosphere leads to the formation of MoNi4:MoOx-3/Nifoam. An iron oxide-hydroxide anode can be prepared by simply dipping the lamina of MoNi4:MoOx-3/Nifoam in a solution of FeCl3. Tests carried out in a complete AEM electrolyzer demonstrate improved performances, showing very good stability with a current loading of 500 mA/cm2 for 1 day at 60°C, keeping the potential around 1.8 V. Further improvements are aimed to bring the current density to 1 A/cm2 maintaining the same cell potential.

Palladium nanoparticles stabilized by a sterically demanding secondary diamine ligand have been synthesized by hydrogen reduction of a palladium acetate complex bearing the corresponding diimine ligand. The obtained nanoparticles were used to catalyze the aerobic oxidation of 1,2-propandiol in n -hexane, and after their heterogenization onto a high surface area carbon, in water. In n -hexane 2,4-dimethyl-1,3-dioxolan-2-yl ( i.e ketal formed between hydroxyacetone and 1,2-propandiol) has been obtained as major product with a selectivity of > 80%, whereas in water acetic acid with a selectivity of > 85% has been achieved. The selectivity switch observed was a clear induced by water. The robustness of diamine-stabilized palladium nanoparticles under real aerobic oxidation conditions has been proved by recycling experiments, TEM measurements of the recovered catalysts and by comparison of its performance with that of palladium nanoparticles generated by the metal vapor synthesis technique and supported onto the same carbon in the absence of the stabilizing diamine ligand.

Hydrogen production using primary renewable energy sources, such as wind, solar, tidal, and so on, is an ideal way to deal with intermittent supply and demand. Electrolytic water splitting is limited by the thermodynamic barrier of water oxidation. Useful levels of hydrogen production can only be obtained with an electrical energy consumption exceeding 45 kW h kg−1 H2. Electrochemical reforming overcomes such thermodynamic limitations by replacing oxygen evolution with the facile oxidation of an alternative substrate. Energy savings of 50% can be obtained using alcohols such as ethanol, ethylene glycol, and glycerol. Electrochemical reforming can be used to exploit the partial oxidation of various alcohols to valuable intermediates of industrial interest. In this way, the production of hydrogen is combined with the biorefinery concept for the combined production of fine chemicals. This short review describes the current status and provides a summary of the steps required to bring the technology to useful application.

Bulk PtSn4 has recently attracted the interest of the scientific community for the presence of electronic states exhibiting Dirac node arcs, enabling possible applications in nanoelectronics. Here, by means of surface-science experiments and density functional theory, we assess its suitability for catalysis by studying the chemical reactivity of the (0 1 0)-oriented PtSn4 surface toward CO, H2O, O2 molecules at room temperature and, moreover, its stability in air. We demonstrate that the catalytic activity of PtSn4 is determined by the composition of the outermost atomic layer. Specifically, we find that the surface termination for PtSn4 crystals cleaved in vacuum is an atomic Sn layer, which is totally free from any CO poisoning. In oxygen-rich environment, as well as in ambient atmosphere, the surface termination is a SnOx skin including SnO and SnO2 in comparable amount. However, valence-band states, including those forming Dirac node arcs, are only slightly affected by surface modifications. The astonishingly beneficial influence of surface oxidation on catalytic activity has been demonstrated by electrocatalytic tests evidencing a reduction of the Tafel slope, from 442 down to 86 mV dec−1, whose origin has been explained by our theoretical model. The use of surface-science tools to tune the chemical reactivity of PtSn4 opens the way toward its effective use in catalysis, especially for hydrogen evolution reaction and oxygen evolution reaction.

The Haber-Bosch process for NH3 production leads to a considerable greenhouse gas release due to the remarkable use of fossil fuels. Therefore, there is an increasing interest in developing alternative and environmental friendly approaches. Among the possible solutions, the electrocatalytic conversion of N 2 has recently gained significant attention; on the other hand, not only scientific but also important technical aspects remain fundamental issues to be clarified. Particularly relevant is the need to improve the analytical protocols to ascertain that any detected NH 3 is actually produced from N 2 rather than from any external contaminations or partial decomposition of the catalyst itself. Here, a rotating ring-disc electrode (RRDE) setup is used for the first time to study the N 2 electroreduction process with the aim to recognize the product species formed at the disc and detected at the ring electrodes, respectively. We demonstrated that this experimental approach is effective to discern also a low-level ammonium concentration through monitoring the ammonia oxidation peak at the ring electrode for a fast and preliminary electrocatalytic performance evaluation and to prevent false positives. The versatility of the RRDE method employed as a fingerprint of new electrocatalyst candidates could allow to reserve time and cost.

The Oxygen Reduction Reaction (ORR) catalyzed by N-carbon electrocatalyst was investigated, focusing on the fundamental features for the selective H2O2 formation. The electrochemical characterization was primarily performed by the use of the Rotating Ring Disk Electrode (RRDE) tool in both hydrodynamic Linear Sweep Voltammetry (LSV) mode and by Chronoamperometry (CA) measurement. We rationalized the structure/activity relationship, reaching a new state-of-the-art in terms of current density for the H2O2 generation. The study also explored the performance in relation with the electrode deposit procedure that is of fundamental importance to achieve a suitable macroscopic electrode preparation. Furthermore, the electrode implementation in a polymer membrane static flow electrolyzer setup, was evaluated to understand how the material catalytic features such as current ranges and selectivity scale up from a classical three electrode system to a more realistic application-focused environment.

Recent advances in developing high-performance anion exchange membranes (AEMs) for fuel cell (AEMFC) applications enable catalyst developers to investigate and test cheaper and/or more sustainable materials under operando fuel cell conditions. In this article, we integrate a high-performance Pd-CeO2/C hydrogen oxidation reaction (HOR) catalyst into AEMFCs in combination with different Pt and Pt-free cathodes. A H2/O2 AEMFC peak power performance of 2 W cm-2 at 80 °C is obtained when using a Pt/C cathode (2 A cm-2 is achieved at a cell voltage of 0.6 V), which translates to 1 W cm-2 peak power density (0.7 A cm-2 is achieved at 0.6 V) at 60 °C with the switch to a cheap, critical raw material (CRM)-free Fe/C cathode catalyst.

Organometallic complexes have intrinsically excellent characteristics as a new class of electrocatalyst for clean energy production in fuel cells and electrolyzers. The state-of-the-art materials for these devices are based on precious metal nanoparticles dispersed on conductive carbon-based supports. Although such materials have reached very high performance levels in terms of activity and stability, they suffer from some intrinsic limitations that contribute to hinder the commercial development of fuel cells and electrolyzers on a large scale. Organometallic-based electrocatalysts may help to overcome such limitations. For example, they exhibit high selectivity in alcohol and sugar electrooxidation. Additionally, precious metal loadings can be reduced significantly using single site organometallic catalysts where each metal atom is potentially active. In this review, we will discuss various literature examples of organometallic electrocatalysts employed as anodes for fuel cells and electrolyzers and as cathodes for the hydrogen evolution reaction (HER). We will focus our attention on the few examples of electrocatalysts that have been successfully used in complete cells.

Novel anion exchange membranes (AEMs) with C-C polymer backbones, cardo fragments, flexible alkyl side chains and cyclic quaternary ammonium (QA) groups were designed and synthesized. Cardo poly(oxindolebiphenylylene) polymers with pendent cyclic QAs of different length (POXIA-Br) were prepared by a superacid-catalysed polyhydroxyalkylation reaction and subsequent quaternion functionalization. This preparation process has the advantages of mild reaction conditions, simple operation, low cost and environmental friendliness. The morphology, water uptake (WU), ion conductivity, stabilities and the fuel cell performance were all investigated thoroughly. With the extension of the side chain length, both the microphase separation scale and the ionic conductivity increased. AEMs with longer pendent QAs exhibited decreased WU and better alkaline stability performance than did AEMs with shorter pendent QAs. POXIH-OH (in OH- form) with a hexyl side-chain spacer showed a maximal conductivity of 73.6 mS cm-1 at 80 °C. There was no degradation observed for POXIH-OH except for loss of 9.5% of QA groups after 1200 h in 1 M NaOH at 80 °C. In addition, the AEM fuel cell test performed a high peak power density of 476 mW cm-2 at 60 °C.

The electrocatalytic conversion of CO 2 to energy-rich chemicals or energy vectors is a highly challenging approach to cope with an ever increasing demand for energy storage and valorization of renewable resources. Herein we report on the electrocatalytic reduction of CO 2 to CO using covalently N-decorated carbon nanotubes as highly efficient and chemoselective metal-free electrocatalysts. At odds with more conventional synthetic methods for the production of N-doped nanocarbons, chemical functionalization warrants a unique control of "surface N-defects" available for the process, ruling out any synergistic contribution to electrocatalysis coming from other surface or bulk N-containing groups. With a CO faradaic efficiency (FE CO ) close to 90% and productivity as high as 48 NL CO g N -1 h -1 , NH-aziridine functionalized MWCNTs have shown CO2RR performance that is among the highest reported so far for related metal-free systems. At the same time, it has offered a unique view-point for the comprehension of the underlying structure-reactivity relationship.

A facile two-step method was developed to synthesize a novel Pd/CeO2/C hybrid electrocatalyst for the hydrogen evolution reaction (HER) in alkaline media. Compared to Pd/C, CeO2/C, and a physical mixture of Pd/C and CeO2/C, the Pd/CeO2 C hybrid exhibited a superior HER electrocatalytic activity. Stable performance of the Pd/CeO2/C hybrid was achieved during a 12 h chronopotentiometry test at 15 mA cm(-2). The improved HER activity and stability can be attributed to the presence of CeO2 not only as a support for anchoring and stabilizing of Pd nanoparticles, but also via strong interaction between Pd and CeO2. Here an intimate contact between Pd and CeO2 nanoparticles and the strong metal support interaction were demonstrated by high resolution transmission electron microscopy (HR-TEM) and X-ray absorption spectroscopy (XAS). The electron transfer from Pd to CeO2 that results in Pd in the oxidized form was also shown by X-ray photoelectron spectroscopy (XPS). The XAS measurements additionally demonstrated that the surface Pd was partially oxidized to Pd oxide, and the formation of a plausible Pd-O-Ce structure in the Pd/CeO2/C hybrid. (C) 2018 The Electrochemical Society.

Small organic molecules such as alcohols and formate salts can be readily transformed into hydrogen and carbon dioxide through electrochemical reforming at low energy cost. In this article methanol and potassium formate are studied for hydrogen production in alkaline anion exchange membrane electroreformers using two anode electrocatalysts, nanoparticle Pd and Rh supported on carbon (5 wt%). Firstly, we report a study of the electrochemical activity of both catalysts in electrochemical test cells at 80 °C. Formate oxidation kinetics are found to be fast on both catalysts. Rh/C shows the best performance for methanol electrooxidation with an onset potential 200 mV lower than Pd/C and a specific activity almost double reaching the value of 2600 A g −1 Rh . The energy cost and conversion efficiency for hydrogen production was determined in complete electrochemical reforming cells at 80 °C using both anode catalysts. The energy costs are low for both substrates ( −1 H2 ) with Pd/C producing hydrogen from potassium formate at an energy cost of 5 KWh kg −1 H2 . Considering both the energy consumption and conversion efficiency (substrate to hydrogen), it is shown that the Rh/C catalyst performs best with methanol as substrate.

4 figures, 4 tables.-- © 2021. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/, In direct alcohol fuel cells (DAFCs), the oxidation of alcohols happens at the expenses of the oxygen reduction reaction at the cathode. DAFCs' cathodes use a significant amount of platinum that is an expensive critical raw material. Moreover, platinum oxidizes alcohols, a fact that combined with alcohol crossover, decreases significantly the performance of the cells. The use of Fe-based (Fesingle bondNsingle bondC) platinum group metal–free (PGM-free) cathodes is a convenient strategy to overcome these limitations. This review analyzes the application of PGM-free cathodes to DAFCs. The discussion focuses on acidic systems and covers the following subjects: (i) the breakdown of DAFC potential in its components, (ii) the analysis of the advantages from the use of the PGM-free cathode, and (iii) a review of the performance and durability of DAFCs. The review closes with a view of the authors of the future perspective for the research., AS gratefully acknowledges financial support from US DOE EERE (DE-EE0008419 ‘Active and Durable PGM-free Cathodic Electrocatalysts for Fuel Cell Application’). EB, AL, AM, and FV gratefully acknowledge financial support from Italian Ministry for University and Research PRIN 2017 (grant no. 2017YH9MRK). CS would like to acknowledge the support from the Italian Ministry of Education, Universities and Research (Ministero dell’Istruzione, dell’Università e della Ricerca – MIUR) through the ‘Rita Levi Montalcini 2018’ Fellowship (grant number: PGR18MAZLI). Financial support from the Italian Ministry of University and Research (MIUR) through grant ‘Dipartimenti di Eccellenza – 2017 – Materials for energy’ is gratefully acknowledged.

Acrylic acid is widely used in the chemical, polymer, cosmetic and food industries. Typically, it is produced through processes with a high environmental impact. In this paper, we demonstrate the co-production of the potassium acrylate salt and hydrogen gas from allyl alcohol in a liquid flow fed anion exchange membrane electrolysis cell operating at 60 °C and ambient pressure. We compare in electrolysis cell tests, two electrocatalysts Pd/C and Pd-CeO2/C evaluating the activity and selectivity for acrylate production. Electrolysis cell parameters are tuned obtaining a maximum conversion of allyl alcohol of 96% and a selectivity to acrylate of 50% at an operating cell voltage of 1 V. Operating at a lower cell potential (0.7 V) the selectivity for acrylate increases to 74%. Hydrogen gas is produced in the separated cathode compartment at an energy cost of 26 KWh kgH2-1, which is around half when compared to state-of-the-art water electrolyzers. The electrochemical oxidation mechanism of allyl alcohol is also studied and discussed, providing for the first time an insight into the pathways for formation of acrylate with respect to the other principle oxidation products (propionate and 3-hydroxypropionate).

Over the last two decades, researchers have found many strategies to obtain high surface area nanostructured titanium dioxide. These nanostructures have recently found application as supports for the fabrication of electrodes for electrochemical energy conversion and storage devices. The properties that make titanium dioxide appealing for these applications are as follows: (i) stability in a variety of conditions relevant to electrocatalysis, (ii) electronic conductivity, (iii) synergistic effects with metal catalysts. The work splits TiO2 nanomaterials into the following two classes: (i) powders and (ii) embedded nanoarchitectures (e.g. titania nanotubes on titanium support). We give an overview of the latest applications, with a special emphasis on fuel cells, electrolysis, and carbon dioxide electroreduction. We conclude with a list of the research needs that, in the opinion of the authors, will support the exploration and consolidation of the use of titania in electrocatalysis for energy.

A critical step in developing deployable water electrolysis technologies is the reduction in the amount of platinum group metals (PGMs) that are the most active catalysts for hydrogen and oxygen evolution. In this paper, we demonstrate a convenient strategy to reduce the PGM loading in electrolysis by using ultra-low Pd loaded electrocatalysts supported on 3D architectures of titania (TiO2) nanotubes. This manuscript focuses on the following aspects: (1) a comprehensive analysis of the synthesis of the TiO2 support using water-based electrolytes; (2) the deposition of Pd catalyst to the support by either physical vapour deposition or dropcast and (3) functional characterisation of the obtained materials for hydrogen and oxygen evolution in both acidic and alkaline environments. A new strategy is developed to obtain short low aspect ratio 3D titania nanotubes arrays (TNTA) and we demonstrate that an extremely low quantity of Pd (81 µg cm−2) is sufficient to obtain significant activity improvement in an Anion Exchange Membrane (AEM) water electrolyser.

The electrochemical reduction of carbon dioxide (CO2RR) is a viable route for the transformation of intermittent renewable energy into high energy density chemical vectors (e.g. CO) or into fuels. Differently from metal nanoparticle electrocatalysts, the use of organometallic molecular complexes affords more efficient metal utilization, limits poisoning phenomena and allows the tuning of selectivity by varying the electronic and coordination properties of the metal center. Herein the organometallic complex (fac-Mn(apbpy)(CO)3Br) (apbpy = 4-(4-aminophenyl)-2,2′-bipyridine) was covalently anchored on a gas diffusion layer which was further employed as cathode in an aqueous gas–liquid interface complete electrolysis flow cell microreactor. The decorated gas diffusion layer electrode was able to convert CO2 into CO and HCOOH with faradaic efficiencies (FE) of 76% and 10% with a CO-productivity close to 70 Nl min−1 gMn−1 reaching CO2RR turnover numbers up to 1.6·105. This result largely outperforms a state-of-the-art gold nanoparticle electrocatalyst (Au/C 10 wt%) operating in the same cell conditions.

The Lewis-acidity of a series of bis-cationic Pt(II)(aqua) complexes bearing phosphane ligands was exploited to catalyze the conversion of dihydroxyacetone to ethyl lactate. The Pt(II) complex bearing 1,2-bis(diphenylphosphanyl)ethane and triflate as counter anion showed high catalytic activity (TOF = 530 h−1) and chemoselectivity (>96%) at 70 °C. On intercalating the latter precatalyst between the lamellae of Na-montmorillonite by a cationic exchange process, high chemoselectivity for ethyl lactate (>99%) at 70 °C was observed, which was maintained in three consecutive catalytic runs.

Electroreforming is a low energy cost technology that combines the production of valuable chemicals from biomass-derived alcohols with the evolution of clean hydrogen at low temperature and atmospheric pressure. The selectivity for the desired chemicals is governed by the nature of the anode catalyst. Here we report the synthesis and characterization of a carbon supported nanostructured Rh electrocatalyst. The Rh nanoparticles are shown to be highly dispersed (2.2 nm) and a complete electrochemical study is reported. This Rh/C catalyst exhibits high activity for alcohol electrooxidation (e.g. 5700 A gRh for EG at 80 °C) and when employed with an anion exchange membrane and Pt/C cathode in an electroreformer produces high volumes of hydrogen at low electrical energy input (e.g. 500 mA cm-2 at 0.7 Vcell and Ecost = 9.6 kW h kgH2-1). A complete analysis of the alcohol oxidation products from several renewable alcohols (ethanol, ethylene glycol, glycerol and 1,2-propandiol) shows a selectivity in the formation of valuable chemicals such as lactate and glycolate.

Ether-bond-free polyfluorene (PBF) anion exchange membranes (AEMs) containing flexible alkyl pendent chains terminated with piperidinium cations were prepared via one-pot, superacid-catalyzed polycondensation and a subsequent quaternization reaction. Hydrophilic and hydrophobic microphase segregation was observed in all AEMs. The hydroxide conductivity of PBF2-Br reaches up to 86 mS cm–1 at 80 °C, and 1H NMR showed no measurable degradation after alkaline treatment in aqueous NaOH (1 M) solution for 1200 h at 80 °C. Besides, a peak power density of 410 mW cm–2 was achieved at 60 °C for an alkaline fuel cell using the selected PBF1-OH (OH– form) as AEM.

Electrocatalytic oxygen reduction (ORR) is an emerging synthetic strategy to prepare H