After confirming Cu as one of the most active electrocatalysts for AP reduction, we set out to broaden the substrate scope of ECH reactions that can be driven by this metal (Fig. ). Following the ECH of a ketone such as AP, we next investigated the ECH of benzaldehyde as an example of aldehyde hydrogenation. Adopting the same reaction conditions (i.e. -0.48 VRHE, pH = 11.8), benzaldehyde was converted into benzyl alcohol on a Cu cathode with a yield of 85% after 3 h electrolysis (Fig. ). Details of the NMR spectra and temporary changes of concentrations can be found in the Supplementary Figures and.