Cost-Effective Hydrogen Oxidation Reaction Catalysts for Hydroxide Exchange Membrane Fuel Cells

Abstract

Fuel cells are clean, efficient energy conversion devices that produce electricity from chemical energy stored within fuels. The development of fuel cells has significantly progressed over the past decades. Specifically, polymer electrolyte fuel cells, which are representative of proton exchange membrane fuel cells (PEMFCs), exhibit high efficiency, high power density, and quick start-up times. However, the high cost of PEMFCs, partially from the Pt-based catalysts they employ, hinders their diverse applicability. Hydroxide exchange membrane fuel cells (HEMFCs), which are also known as alkaline polymer electrolyte fuel cells (APEFCs), alkaline anionexchange membrane fuel cells (AAEMFCs), anion exchange membrane fuel cells (AEMFCs), or alkaline membrane fuel cells (AMFCs), have attracted much attention because of their capability to use non-Pt electrocatalysts and inexpensive bipolar plates. The HEMFCs are structurally similar to PEMFCs but they use a polymer electrolyte that conducts hydroxide ions, thus providing an alkaline environment. However, the relatively sluggish kinetics of the hydrogen oxidation reaction (HOR) inhibit the practical application of HEMFCs. The anode catalyst loading needed for HEMFCs to achieve high cell performance is larger than that required for other fuel cells, which substantially increases the cost of HEMFCs. Therefore, low-cost, highly active, and stable HOR catalysts in the alkaline condition are greatly desired. Here, we review the recent achievements in developing such HOR catalysts. First, plausible HOR mechanisms are explored and HOR activity descriptors are summarized. The HOR processes are mainly controlled by the binding energy between hydrogen and the catalysts, but they may also be influenced by OH adsorption, interfacial water adsorption, and the potential of zero (free) charge. Next, experimental methods used to elevate HOR activities are introduced, followed by HOR catalysts reported in the literature, including Pt-, Ir-, Pd-, Ru-, and Ni-based catalysts, among others. HEMFC performances when employing various anode catalysts are then summarized, where HOR catalysts with platinum-group metals exhibited the highest HEMFC performance. Although the Ni-based HOR catalyst activity was higher than those of other non-precious metalbased catalysts, they showed unsatisfactory performance in HEMFCs. We further analyzed HEMFC performances while considering anode catalyst cost, where we found that this cost can be reduced by using recently developed, non-Pt HOR catalysts, especially Ru-based catalysts. In fact, an HEMFC using a Ru-based HOR catalyst showed an anode catalyst cost-based performance similar to that of PEMFCs, making the HEMFC promising for use in practical applications. Finally, we proposed routes for developing future HOR catalysts for HEMFCs.

Lattice Oxygen-Induced d-Band Shifting for Enhanced Hydrogen Oxidation Reaction on Nickel

“…Large-scale application of proton exchange membrane fuel cells (PEMFCs) is still hindered by the high cost of proton exchange membranes and platinum-based precious metal catalysts used for both electrodes. , In contrast, alkaline anion-exchange membrane fuel cells (AEMFCs) have the potential to break through these bottlenecks for available low-cost anion-exchange membranes and functional non-precious electrocatalysts for the cathodic reaction . However, the 2–3 orders of magnitude slower hydrogen oxidation reaction (HOR) kinetics on platinum group metal (PGM) catalysts in an alkaline environment necessitate a higher loading of PGM catalysts to maintain the energy output of AEMFCs comparable to PEMFCs, eventually making the overall cost unaffordable. , These limitations motivate extensive research in developing highly efficient low-loading PGM or PGM-free HOR electrocatalysts in alkaline electrolytes. , …”

“…5,6 These limitations motivate extensive research in developing highly efficient low-loading PGM or PGM-free HOR electrocatalysts in alkaline electrolytes. 7,8 One of the common strategies to reduce cost is to dope nonnoble metals into PGM catalysts, which has achieved favorable progress in reducing precious metal loadings without distinctly damaging the activities of the electrocatalysts. 9 For example, the HOR activity and PGM loading amount of Pt/CuNWs, 10 BCC-phased PdCu alloy, 11 and RuNi 12,13 can be adjusted through tuning the proportions of mixed components.…”

Electrocatalytic Hydrogen Oxidation in Alkaline Media: From Mechanistic Insights to Catalyst Design

“…Given these considerations, we herein aim at providing an in-depth analysis of the recent advances in high-performance electrocatalysts for HOR in alkaline media. Despite several previous reviews elsewhere summarizing the developments regarding the alkaline HOR from reaction mechanism and structural design aspects, ,− a deep understanding of the relationship between the binding energies of the reaction intermediates and the electrocatalytic activities is still highly desirable. Beyond that, it should be noted that some representative electrocatalysts demonstrate considerable HOR activity, whereas the antioxidation ability is less desirable or left unmentioned, which deserves in-depth exploration.…”

Ruthenium nanoparticles supported on Ni3N nanosheets as bifunctional electrocatalysts for hydrogen oxidation/evolution reactions

“…Over the past few decades, hydrogen energy has emerged as an eco-friendly alternative to fossil fuel energy. 1 Notably, protonexchange membrane fuel cells, as the most promising cell technology, are severely constrained by high-cost Pt-based catalysts and peruorinated membranes. [2][3][4][5][6] Since the highly stable hydroxide exchange membrane was reported, 7 anionexchange membrane fuel cells (AEMFCs) have attracted much attention because they provide the possibility to use low-cost non-noble metal catalysts for alkaline ORR.…”