Abstract
Hydroxide exchange membrane fuel cells offer possibility of adopting platinum-group-metal-free catalysts to negotiate sluggish oxygen reduction reaction. Unfortunately, the ultrafast hydrogen oxidation reaction (HOR) on platinum decreases at least two orders of magnitude by switching the electrolytes from acid to base, causing high platinum-group-metal loadings. Here we show that a nickel-molybdenum nanoalloy with tetragonal MoNi4 phase can catalyze the HOR efficiently in alkaline electrolytes. The catalyst exhibits a high apparent exchange current density of 3.41 milliamperes per square centimeter and operates very stable, which is 1.4 times higher than that of state-of-the-art Pt/C catalyst. With this catalyst, we further demonstrate the capability to tolerate carbon monoxide poisoning. Marked HOR activity was also observed on similarly designed WNi4 catalyst. We attribute this remarkable HOR reactivity to an alloy effect that enables optimum adsorption of hydrogen on nickel and hydroxyl on molybdenum (tungsten), which synergistically promotes the Volmer reaction.
Highlights
Hydroxide exchange membrane fuel cells offer possibility of adopting platinum-group-metalfree catalysts to negotiate sluggish oxygen reduction reaction
Hydroxide exchange membrane fuel cells (HEMFCs) give critical merits over proton exchange membrane fuel cell (PEMFC), which permit the adoption of Pt group metal (PGM)-free catalysts to negotiate the formidable ORR3–5, leading to substantial cost reduction
Numerous efforts have been devoted to developing PGM-free catalysts for alkaline hydrogen oxidation reaction (HOR) since 1960s36, no catalyst with activity superior to commercial Pt/C has been reported, which severely limits their practical adoption in hydroxide exchange membrane fuel cells (HEMFCs)
Summary
Hydroxide exchange membrane fuel cells offer possibility of adopting platinum-group-metalfree catalysts to negotiate sluggish oxygen reduction reaction. Marked HOR activity was observed on designed WNi4 catalyst We attribute this remarkable HOR reactivity to an alloy effect that enables optimum adsorption of hydrogen on nickel and hydroxyl on molybdenum (tungsten), which synergistically promotes the Volmer reaction. The nanostructured MoNi4 catalyst yields a geometric exchange current density of 3.41 mA cm−2 towards the HOR, which is 1.4 times higher than that of commercial Pt/C catalyst and compares superior to previously reported PGM-free catalysts measured in alkali. At 50 mV, a geometric kinetic current density of 33.8 mA cm−2 is obtained for MoNi4 catalyst, which represents 105- and 2.8-fold increase as compared to the freshly synthesized Ni and commercial Pt/C catalyst, respectively This alloy catalyst shows impressive tolerance against surface poisoning by impurity carbon monoxide (CO) in hydrogen fuel. Our results suggest a promising alloy design strategy for producing active and durable HOR catalysts for lowcost HEMFC anodes
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