Dynamic Active‐Hydrogen‐Buffering Interfaces Enable Fluctuation‐Resilient Selective Electrocatalytic Hydrogenation

Renewable‐electricity‐driven electrocatalysis is difficult to maintain under steady‐state operation because of the intermittent, variable, and stochastic nature of renewable power. This challenge is particularly critical for selective electrocatalytic hydrogenation (ECH), such as phenol‐to‐cyclohexanone conversion in acidic media, where fluctuating operation can induce transient accumulation of active hydrogen intermediates, compromising product selectivity and energy efficiency. In this study, we develop a dynamic active‐hydrogen‐buffering interface strategy to construct fluctuation‐resistant electrocatalysts using the short‐chain surfactant butyltrimethylammonium bromide (BTAB). Under simulated power fluctuations in a flow cell, the BTAB‐modified catalyst maintains near‐steady‐state performance, achieving 90.1% cyclohexanone selectivity and 83.6% Faradaic efficiency (FE), and outperforms the unmodified system by 1.69‐fold in cyclohexanone FE under more drastic fluctuations. Mechanistic studies reveal that the BTAB layer weakens the interfacial hydrogen‐bond network and attenuates Grotthuss‐type proton relay, thereby regulating proton flux and buffering active hydrogen accumulation during current fluctuations. This suppresses competing hydrogen evolution and overhydrogenation to cyclohexanol while preserving phenol hydrogenation kinetics. Combined with techno‐economic analysis, this work establishes active‐hydrogen buffering as an interfacial strategy for maintaining selective electrosynthesis under dynamic operating conditions.