A detailed perspective on the use of anion-exchange membranes in fuel cells, electrolysers, flow batteries, reverse electrodialysis, and bioelectrochemical systems.

For the large-scale sustainable implementation of polymer electrolyte membrane fuel cells in vehicles, high-performance electrocatalysts with low platinum consumption are desirable for use as cathode material during the oxygen reduction reaction in fuel cells. Here we report a carbon black-supported cost-effective, efficient and durable platinum single-atom electrocatalyst with carbon monoxide/methanol tolerance for the cathodic oxygen reduction reaction. The acidic single-cell with such a catalyst as cathode delivers high performance, with power density up to 680 mW cm−2 at 80 °C with a low platinum loading of 0.09 mgPt cm−2, corresponding to a platinum utilization of 0.13 gPt kW−1 in the fuel cell. Good fuel cell durability is also observed. Theoretical calculations reveal that the main effective sites on such platinum single-atom electrocatalysts are single-pyridinic-nitrogen-atom-anchored single-platinum-atom centres, which are tolerant to carbon monoxide/methanol, but highly active for the oxygen reduction reaction.

In recent decades, fuel cell technology has been undergoing revolutionary developments, with fundamental progress being the replacement of electrolyte solutions with polymer electrolytes, making the device more compact in size and higher in power density. Nowadays, acidic polymer electrolytes, typically Nafion, are widely used. Despite great success, fuel cells based on acidic polyelectrolyte still depend heavily on noble metal catalysts, predominantly platinum (Pt), thus increasing the cost and hampering the widespread application of fuel cells. Here, we report a type of polymer electrolyte fuel cells (PEFC) employing a hydroxide ionconductive polymer, quaternary ammonium polysulphone, as alkaline electrolyte and nonprecious metals, chromium-decorated nickel and silver, as the catalyst for the negative and positive electrodes, respectively. In addition to the development of a high-performance alkaline polymer electrolyte particularly suitable for fuel cells, key progress has been achieved in catalyst tailoring: The surface electronic structure of nickel has been tuned to suppress selectively the surface oxidative passivation with retained activity toward hydrogen oxidation. This report of a H2-O2 PEFC completely free from noble metal catalysts in both the positive and negative electrodes represents an important advancement in the research and development of fuel cells.nonprecious metals ͉ hydrogen oxidation ͉ oxygen reduction F uel cells have been recognized as an alternative powergeneration technique for the future in both mobile and stationary uses (1, 2). After decades of evolution, fuel cells of various types have been developed (2), such as alkaline fuel cell (AFC), phosphoric acid fuel cell (PAFC), molten carbonate fuel cell (MCFC), solid oxide fuel cell (SOFC), and polymer electrolyte fuel cell (PEFC). Among them, PEFC has been the most developed one in the past 2 decades (3), featuring rapid startup and high power density particularly suitable for vehicle applications (1-3).Compared with the aqueous electrolytes traditionally used in low-temperature fuel cells, polymer electrolytes completely eliminate the problems caused by electrolyte leakage and can effectively separate the fuels (such as hydrogen) and the oxidant (oxygen) with a thin film of a few tens of microns in thickness. For decades, the commonly used polymer electrolytes have been limited to proton exchange membranes, typically Nafion . Nowadays, many Nafion-based fuel cell systems of different sizes are being demonstrated or tested on a variety of applications across the world. Although they are promising, the Nafion-based fuel cells still face a number of obstacles to commercialization, one of which has been the severe dependence of catalysts on platinum (Pt), an expensive and scarce resource in the earth. Such dependence stems from the strong acidic nature of the protonexchange membrane; and thermodynamically, only noble metals can be relatively stable in this corrosive environment. Despite tremendous efforts devoted to the search for non-...

Pd has been the focus of recent research for Pt-alternative catalysts for the oxygen reduction reaction (ORR). It has been found that upon appropriate modification of its electronic structure, the catalytic activity of Pd can become comparable to that of Pt. However, the structure-activity relationships of Pd catalysts have hitherto not been well studied or understood. In the present work, we report a new finding that there is a strong dependence of the activity of Pd toward the ORR on its morphology. By simply adjusting the precursor concentration in the electrochemical deposition of Pd, we are able to tailor the morphology of the deposited Pd from nanoparticles to nanorods. Surprisingly, the surface-specific activity of Pd nanorods (Pd-NRs) toward the ORR was found to be not only 10-fold higher than that of Pd nanoparticles (Pd-NPs), the conventional shape of electrocatalysts, but also comparable to that of Pt at operating potentials of fuel cell cathodes. The morphology-activity relationships of Pd-NRs were further studied through a combination of electrochemical experiments and density functional theory (DFT) calculations. As revealed by its characteristic profile for CO stripping, the morphology of Pd-NRs features the exposure of Pd(110) facets, which exhibit superior ORR activity. The underlying mechanism, indicated by DFT calculations, could be ascribed to the exceptionally weak interaction between an O adatom and a Pd(110) facet. This finding furthers our understanding of Pd catalysis and casts a new light on the relevant catalyst design criteria.