Abstract
The top-down fabrication of catalytically active molecular metal oxide anions, or polyoxometalates, is virtually unexplored, although these materials offer unique possibilities, for catalysis, energy conversion and storage. Here, we report a novel top-down route, which enables the scalable synthesis and deposition of sub-nanometer molybdenum-oxo clusters on electrically conductive mesoporous carbon. The new approach uses a unique redox-cycling process to convert crystalline MoIVO2 particles into sub-nanometer molecular molybdenum-oxo clusters with a nuclearity of ∼1–20. The resulting molybdenum-oxo cluster/carbon composite shows outstanding, stable electrocatalytic performance for the oxygen reduction reaction with catalyst characteristics comparable to those of commercial Pt/C. This new material design could give access to a new class of highly reactive polyoxometalate-like metal oxo clusters as high-performance, earth abundant (electro-)catalysts.
Highlights
IntroductionThe ideal scenario is the maximum dispersion of accessible reactive sites on the electrode surface
Many catalytic processes in energy conversion, such as electrolysis, fuel cells and metal–air batteries, rely on the stable immobilization of highly active metal reaction centers on electrically conductive high surface-area electrodes.[1,2,3] A prime example is the oxygen reduction reaction (ORR) which is performed in commercial systems using precious metal catalysts such as platinum to accelerate the sluggish reaction kinetics
The new composites are synthesized using a hard-templating route,[38] where a commercial mesoporous silica template is impregnated with aqueous solutions containing sucrose as the carbon precursor and precursor [H3PMo12O40] (PMo12) as the Brønsted-acidic carbonization catalyst and metal-oxo source
Summary
The ideal scenario is the maximum dispersion of accessible reactive sites on the electrode surface. To remove the silica template, the asprepared composites were stirred in 50 mL of 10% aqueous hydro uoric acid (HFaq, $ 48%, Sigma-Aldrich) for 48 h, and washed with water and ethanol three times respectively, and nally dried at 100 C overnight. During this step, PMo12 was reduced and converted to MoO2, while the subsequent HF treatment did not signi cantly affect the chemical makeup of the molybdenum-based species in 1. For 0.1 M aqueous KOH, ERHE 1⁄4 EAg/AgCl + 0.977 V and ERHE 1⁄4 EHg/HgO + 0.883 V
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