Dual hydrogen production from electrocatalytic water reduction coupled with formaldehyde oxidation via a copper-silver electrocatalyst.

The broad employment of water electrolysis for hydrogen (H) production is restricted by its large voltage requirement and low energy conversion efficiency because of the sluggish oxygen evolution reaction (OER). Herein, we report a strategy to replace OER with a thermodynamically more favorable reaction, the partial oxidation of formaldehyde to formate under alkaline conditions, using a CuAg electrocatalyst. Such a strategy not only produces more valuable anodic product than O but also releases H at the anode with a small voltage input. Density functional theory studies indicate the HC(OH)O intermediate from formaldehyde hydration can be better stabilized on CuAg than on Cu or Ag, leading to a lower C-H cleavage barrier. A two-electrode electrolyzer employing an electrocatalyst of CuAg(+)||NiN/Ni(-) can produce H at both anode and cathode simultaneously with an apparent 200% Faradaic efficiency, reaching a current density of 500 mA/cm with a cell voltage of only 0.60 V.