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

The broad employment of water electrolysis for hydrogen (H2) 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 Cu3Ag7 electrocatalyst. Such a strategy not only produces more valuable anodic product than O2 but also releases H2 at the anode with a small voltage input. Density functional theory studies indicate the H2C(OH)O intermediate from formaldehyde hydration can be better stabilized on Cu3Ag7 than on Cu or Ag, leading to a lower C-H cleavage barrier. A two-electrode electrolyzer employing an electrocatalyst of Cu3Ag7(+)||Ni3N/Ni(-) can produce H2 at both anode and cathode simultaneously with an apparent 200% Faradaic efficiency, reaching a current density of 500 mA/cm2 with a cell voltage of only 0.60 V.