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.