Green electricity-driven alkenol electrosynthesis via electrocatalytic alkynol semihydrogenation represents a sustainable route to conventional thermocatalysis. Both the electrocatalyst and electrolyte strongly impact the semihydrogenation performance. Despite significant progress in developing sophisticated electrocatalysts, a well-designed electrolyte in conjunction with industrial catalysts is an attractive strategy to advance the industrialization process of electrocatalytic alkynol semihydrogenation, but remains unexplored. Here, we develop a dimethyl sulfoxide (DMSO)-H2O cosolvent electrolyte for electrocatalytic alkynol semihydrogenation. At an alkynol conversion of about 100%, the DMSO-H2O electrolyte compared to the DMSO-free counterpart enables the alkenol selectivity on Cu catalysts to be promoted from 60-70% to over 90% at all measured current densities; meanwhile, the reaction rate is slightly decreased due to the inhibited water dissociation. Mechanistic studies reveal that the strong hydrogen-bond interactions between DMSO and H2O suppress the dissociation of interfacial H2O, leading to a decreased H* coverage at the electrode surface. The decreased H* coverage hinders the overhydrogenation of alkynols and favors the production of alkenols. Remarkably, the DMSO-induced enhancement of alkenol selectivity is applicable to a set of commercial catalysts and to the semihydrogenation of various alkynols. Eventually, a scaled-up 3 × 100 cm2 electrolyzer stack is established to achieve an alkynol conversion of ∼96% and an alkenol selectivity of ∼95% in the cosolvent electrolyte. This work not only presents an electrolyte strategy for boosting alkenol electrosynthesis, but also highlights the possibility of sustainable alkenol electro-production.