Nitrate　electroreduction　is　promising　for　achieving　effluent　waste-water　treatment　and　ammonia　production　with　respect　to　the　global　nitrogen　balance.　However,　due　to　the　impeded　hydrogenation　process,　high　overpotentials　need　to　be　surmounted　during　nitrate　electroreduction,　causing　intensive　energy　consumption.　Herein,　a　hydroxide　regulation　strategy　is　developed　to　optimize　the　interfacial　H2O　behavior　for　accelerating　the　hydrogenation　conversion　of　nitrate　to　ammonia　at　ultralow　overpotentials.　The　well-designed　Ru─Ni(OH)2　electrocatalyst　shows　a　remarkable　energy　efficiency　of　44.6%　at　+0.1 V　versus　RHE　and　a　nearly　100%　Faradaic　efficiency　for　NH3　synthesis　at　0 V　versus　RHE.　In　situ　characterizations　and　theoretical　calculations　indicate　that　Ni(OH)2　can　regulate　the　interfacial　H2O　structure　with　a　promoted　H2O　dissociation　process　and　contribute　to　the　spontaneous　hydrogen　spillover　process　for　boosting　NO3−　electroreduction　to　NH3　at　Ru　sites.　Furthermore,　the　assembled　rechargeable　Zn-NO3−/ethanol　battery　system　exhibits　an　outstanding　long-term　cycling　stability　during　the　charge–discharge　tests　with　the　production　of　high-value-added　ammonium　acetate,　showing　great　potential　for　simultaneously　achieving　nitrate　removal,　energy　conversion,　and　chemical　synthesis.　This　work　can　not　only　provide　a　guidance　for　interfacial　H2O　regulation　in　extensive　hydrogenation　reactions　but　also　inspire　the　design　of　a　novel　hybrid　flow　battery　with　multiple　functions.　©　2025　Wiley-VCH　GmbH.