Unusual Effect of Trace Water on the Structure and Activity of NixCo1−x Electrocatalysts for the Methanol Oxidation Reaction

Graphical Just add water : A mere trace of water roughly halves the size and regulates the composition of polyhedral Ni x Co 1− x alloy nanoparticles prepared by the polyol method. The Ni 0.6 Co 0.4 nanoparticle alloy obtained by adding 70 μL of water shows superior electrocatalytic performance in the methanol oxidation reaction owing to its appropriate Ni/Co ratio and is a promising electrocatalyst for use in direct methanol fuel cells. Highly active Ni-based catalysts have attracted much attention but are still facing challenges owing to the immature synthetic method. Herein, polyhedral Ni x Co 1− x alloy was prepared by a facile modified polyol method in which a trace amount of water could halve the particle size of the alloy. The Ni/Co ratios in Ni x Co 1− x alloy strictly depended on the used amount of water owing to the different solubilities of the precursors. Among them, the Ni 0.6 Co 0.4 nanoparticles obtained with 70 μL of deionized water exhibited the best performance in the methanol oxidation reaction with a peak current density of 116 mA cm −2 in the presence of 1 m NaOH+0.5 m CH 3 OH solution, which is higher than those of Ni 0.7 Co 0.3 (80 mA cm −2 ) and Ni 0.5 Co 0.5 (33 mA cm −2 ). The excellent performance of Ni 0.6 Co 0.4 is attributed to the unique structure with appropriate Ni/Co ratio, which elongates the C−O bond in methanol and lowers the reaction free energy according to DFT calculations.