Electrocatalytic semi-hydrogenation of alkynes to alkenes using low-cost precious metal-free catalysts with water as the hydrogen source is ideal, but challenging because of their over-hydrogenation to unwanted alkanes. Here, we propose that the ideal catalyst should have appropriate binding energy with active atomic hydrogen (H*) from hydroelectrolysis and weak adsorption with alkenes, thus promoting semi-hydrogenation of alkynes and avoiding over-hydrogenation.