Suppression of the Hydrogen Evolution Reaction Is the Key: Selective Electrosynthesis of Formate from CO over Porous InCu Catalysts.

Direct electrosynthesis of formate through CO electroreduction (denoted CORR) is currently attracting great attention because formate is a highly valuable commodity chemical that is already used in a wide range of applications (e.g., formic acid fuel cells, tanning, rubber production, preservatives, and antibacterial agents). Herein, we demonstrate highly selective production of formate through CORR from a CO-saturated aqueous bicarbonate solution using a porous InCu alloy as the electrocatalyst. This novel high-surface-area material was produced by means of an electrodeposition process utilizing the dynamic hydrogen bubble template approach. Faradaic efficiencies (FEs) of formate production (FE) never fell below 90% within a relatively broad potential window of approximately 400 mV, ranging from -0.8 to -1.2 V the reversible hydrogen electrode (RHE). A maximum FE of 96.8%, corresponding to a partial current density of = -8.9 mA cm, was yielded at -1.0 V RHE. The experimental findings suggested a CORR mechanism involving stabilization of the HCOO* intermediate on the InCu alloy surface in combination with effective suppression of the parasitic hydrogen evolution reaction. What makes this CORR alloy catalyst particularly valuable is its stability against degradation and chemical poisoning. An almost constant formate efficiency of ∼94% was maintained in an extended 30 h electrolysis experiment, whereas pure In film catalysts (the reference benchmark system) showed a pronounced decrease in formate efficiency from 82% to 50% under similar experimental conditions. The identical location scanning electron microscopy approach was applied to demonstrate the structural stability of the applied InCu alloy foam catalysts at various length scales. We demonstrate that the proposed catalyst concept could be transferred to technically relevant support materials (e.g., carbon cloth gas diffusion electrode) without altering its excellent figures of merit.