One of the biggest obstacles to the dissemination of fuel cells is their cost, a large part of which is due to platinum (Pt) electrocatalysts. Complete removal of Pt is a difficult if not impossible ...task for proton exchange membrane fuel cells (PEM‐FCs). The anion exchange membrane fuel cell (AEM‐FC) has long been proposed as a solution as non‐Pt metals may be employed. Despite this, few examples of Pt‐free AEM‐FCs have been demonstrated with modest power output. The main obstacle preventing the realization of a high power density Pt‐free AEM‐FC is sluggish hydrogen oxidation (HOR) kinetics of the anode catalyst. Here we describe a Pt‐free AEM‐FC that employs a mixed carbon‐CeO2 supported palladium (Pd) anode catalyst that exhibits enhanced kinetics for the HOR. AEM‐FC tests run on dry H2 and pure air show peak power densities of more than 500 mW cm−2.
Low‐cost cell: A platinum‐free alkaline membrane fuel cell employing a Pd/C‐CeO2 anode electrocatalyst produces peak power densities of more than 500 mW cm−2. Morphological analysis attests to a fine dispersion of the Pd nanoparticles accumulated mostly on the ceria part of the catalyst.
•Discusses hydrogen oxidation reaction kinetics in anion exchange membrane fuel cells.•CeO2-Pd nanocomposites supported on conductive carbon exhibit enhanced activity.•Various synthetic methods have ...been developed to prepare Pd-CeO2/C materials.•Enhanced HOR activity is linked to maximized Pd-CeO2-C interfacial contact area.•Computational studies point to a bi-functional HOR mechanism on Pd-CeO2.•Pd-CeO2/C shows enhanced activity also for alcohol oxidation at high pH.
In 2016, for the first time a polymer electrolyte fuel cell free of Pt electrocatalysts was shown to deliver more than 0.5 W cm−2 of peak power density from H2 and air (CO2 free). This was achieved with a silver-based oxygen reduction (ORR) cathode and a Pd-CeO2 hydrogen oxidation reaction (HOR) anodic electrocatalyst. The poor kinetics of the HOR under alkaline conditions is a considerable challenge to Anion Exchange Membrane Fuel Cell (AEMFC) development as high Pt loadings are still required to achieve reasonable performance. Previously, the ameliorative combination of Pd and CeO2 nanocomposites has been exploited mostly in heterogeneous catalysis where the positive interaction is well documented. Carbon supported Pd-CeO2 HOR catalysts have now been prepared by different synthetic techniques and employed in AEMFCs as alternative to Pt and PtRu standards. Important research has also been recently reported, delving into the origin of the HOR enhancement on Pd-CeO2. Such work has highlighted the importance of the bifunctional mechanism of the HOR at high pHs. Carefully prepared nano-structures of Pd and CeO2 that promote the formation of the Pd-O-Ce interface provide optimal binding of both Had and OHad species, aspects which are crucial for enhanced HOR kinetics. This review paper discusses the recent advances in Pd-CeO2 electrocatalysts for AEMFC anodes.
We report an interesting new class of bifunctional electrocatalysts, Pd/C-CeO2, with excellent activity and stability for the hydrogen oxidation reaction (HOR) under alkaline conditions. The unique ...structure of palladium deposited onto a mixed support of Vulcan XC-72 carbon and CeO2 consists of Pd metal preferable deposited on the ceria regions of the catalyst. The CeO2-Pd interaction leads to enhanced HOR kinetics and increased stability. Here we compare catalysts with three different Pd loadings and show that the 10wt% Pd sample has optimized activity. Hydrogen pumping and fuel cell experiments based on this catalyst show higher activities as compared to a Pd/C sample without ceria. Metal dissolution tests and identical location transmission microscopy experiments show that the catalyst stability under harsh potential cycling experiments in alkaline medium is significantly improved as compared to Pd/C, making this material one of the best options for use as highly active and highly stable electrocatalysts for the HOR in anion exchange membrane fuel cells.
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•A new class of electrocatalyst for H2 oxidation in alkaline media is described.•Unique structure of Pd deposited on a mixed support of carbon and CeO2.•Hydrogen pump and fuel cell tests show enhanced activity.•Identical location transmission electron microscopy show improved stability.
Electrochemical oxygen reduction (ORR) is a challenging approach for the sustainable production of hydrogen peroxide (H2O2) and is also a reaction of relevance in fuel-cell applications. Here, we ...propose an outstanding metal-free electrocatalyst for the unexpectedly selective ORR to H2O2, consisting of graphitized N-doped single-wall carbon nanohorns (CNHs). The catalyst can operate at acidic pH to a faradic efficiency as high as 98%, but it also shows excellent performance at either physiological or alkaline pH. Moreover, the very positive onset potentials observed at all pH values investigated (+0.40 V, +0.53 V, and +0.71 V at pH 1.0, 7.4, and 13.0, respectively), good stability, and excellent reproducibility make this material a benchmark catalyst for ORR to H2O2. The outstanding activity arises from a combination of several factors, such as CNH-dependent facilitation of electron delivery, suitable porosity, and a favorable distribution of the types of N atoms.
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•A metal-free electrocatalyst for the reduction of O2 is prepared•The catalysts displays high selectivity toward the formation of H2O2•The catalyst's selectivity remains excellent over a wide pH range
The versatility of hydrogen peroxide as a chemical for a wide range of applications justifies its heavy industrial production. Hydrogen peroxide is currently produced through the anthraquinone process, which is an energy-intensive process relying on the use of a precious metal (palladium). Therefore, there is huge interest in finding alternative low-cost and low-energy synthetic schemes. Electrocatalytic processes exploiting the reduction of molecular O2 are undoubtedly of high appeal, particularly if they can rely on electrocatalysts based on metal-free materials.
The electrocatalytic reduction of O2 is also of high interest from an energy perspective for fuel-cell development. Hence, the development of an electrocatalyst able to selectively reduce O2 to H2O2 potentially has a double utility, provided that the catalytic reaction occurs at low applied overpotentials and the material possesses long-term stability and high current efficiency.
Fornasiero and colleagues describe an alternative strategy for producing hydrogen peroxide through a more sustainable method than the current synthetic approaches. The strategy relies on the use of electrocatalysis, made possible by the use of a catalyst with high efficiency and selectivity toward H2O2 formation. The prepared material is particularly appealing because it does not contain any metal, implying a greener and cheaper synthetic scheme.
The selective conversion of ethanol into potassium acetate with concomitant production of electrical energy has been achieved in both passive and active direct fuel cells containing platinum-free ...electrodes and an anion-exchange polymer membrane. The power densities supplied by the passive systems at r.t. can be as high as 55
mW
cm
−2, while the active systems can deliver up to 170
mW
cm
−2 at 80
°C. Such high values have never been reported for direct ethanol fuel cells with whatsoever electrocatalyst in either alkaline or acidic media.
The electrooxidation of ethylene glycol (EG) and glycerol (G) has been studied: in alkaline media, in passive as well as active direct ethylene glycol fuel cells (DEGFCs), and in direct glycerol fuel ...cells (DGFCs) containing Pd‐(Ni‐Zn)/C as an anode electrocatalyst, that is, Pd nanoparticles supported on a Ni–Zn phase. For comparison, an anode electrocatalyst containing Pd nanoparticles (Pd/C) has been also investigated. The oxidation of EG and G has primarily been investigated in half cells. The results obtained have highlighted the excellent electrocatalytic activity of Pd‐(Ni‐Zn)/C in terms of peak current density, which is as high as 3300 A g(Pd)−1 for EG and 2150 A g(Pd)−1 for G. Membrane‐electrode assemblies (MEA) have been fabricated using Pd‐(Ni‐Zn)/C anodes, proprietary Fe‐Co/C cathodes, and Tokuyama A‐201 anion‐exchange membranes. The MEA performance has been evaluated in either passive or active cells fed with aqueous solutions of 5 wt % EG and 5 wt % G. In view of the peak‐power densities obtained in the temperature range from 20 to 80 °C, at Pd loadings as low as 1 mg cm−2 at the anode, these results show that Pd‐(Ni‐Zn)/C can be classified amongst the best performing electrocatalysts ever reported for EG and G oxidation.
An excellent electrocatalyst! The electrooxidation of ethylene glycol (EG) and glycerol (G) has been studied, in alkaline media, in passive as well as active direct ethylene glycol fuel cells and direct glycerol fuel cells containing Pd‐(Ni‐Zn)/C as anode electrocatalyst, that is, Pd nanoparticles supported on a Ni–Zn phase. Pd‐(Ni‐Zn)/C can be classified amongst the best performing Pd‐based electrocatalysts ever reported for EG and G oxidation.
•Pd catalysts deactivates in the alkaline electro-oxidation of alcohols.•Deactivation is related to the anodic stress of catalyst.•Catalyst deactivation is ascribed to the oxidation of Pd.•Catalyst ...service life can be improved by a suitable choice of operating conditions.
Deactivation is one the main causes still preventing the full exploitation of palladium electrocatalysts in alkaline direct alcohol fuel cells and the electrochemical reforming of alcohols. While often attributed to the adsorption of poisoning species generated in the alcohols oxidation, in the present work we demonstrate that deactivation is provoked by the formation of palladium oxides. A combined approach including i) fuel cell runs, ii) cyclic voltammetry and iii) near edge X-ray absorption spectroscopy has enabled us to draw the conclusions reported in the paper.
A feasibility analysis, to assess the suitability of converting the biogas produced in an existing anaerobic digestion plant to bio-methane, was carried out. The case study plant was equipped with a ...micro-gas turbine co-generator. Several upgrading systems of different sizes were considered, to determine the most suitable configuration from a thermodynamic and economic point of view. For this purpose, a model of the whole plant that included digesters, a micro-gas turbine, a sludge line, heat transfer loops, and heat exchangers was developed. A steady-state simulation was performed by using the daily average conditions for the one-year long operation of the plant. The results highlighted that the feasibility depended on the amount of bio-methane produced, as this affected the performance of the cogeneration system and the balance between the costs and revenues. When large amounts of biogas are upgraded to bio-methane, the heat provided by the micro-gas turbine during the winter season is not sufficient to keep the digesters at the desired temperature and, therefore, natural gas integration is necessary. In addition, by increasing the upgrading unit size, the amount of electric energy purchased by the grid increases accordingly. An economic analysis showed that the optimal upgrading system size was strongly dependent on the bio-methane selling price.
Here we review recent developments and technological advances in the field of electrochemical reduction of carbon dioxide to fuels, energy carriers and precursors and other interesting building ...blocks for industrial applications. Synthetic hydrocarbon fuels derived from CO2/H2O are proposed as alternatives to hydrogen as an energy carrier that enables a carbon‐neutral energy cycle, given their inherent advantages of high H/C ratio and convenience of storage and transportation. The electrochemical reduction of CO2 represents a feasible route for the direct generation of hydrocarbon fuels or their precursors (i.e., synthesis gas) using CO2/H2O. Such hydrocarbons fit well within the existing energy infrastructure because of their similarity to existing fossil fuels. Recently significant efforts are being devoted to the development of prototype systems, such as low‐ or high‐ temperature electrolyzers that operate as part of environmentally sustainable energy networks.
Reducing CO2: Synthetic hydrocarbon fuels derived from CO2/H2O are proposed as alternatives to hydrogen as an energy carrier that enables a carbon‐neutral energy cycle. The electrochemical reduction of CO2 represents a feasible route for the direct generation of hydrocarbon fuels or their precursors (i.e., synthesis gas). Such hydrocarbons fit well within the existing energy infrastructure because of their similarity to existing fossil fuels.
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