Potential-Controlled Selective Electrocatalytic Reduction of Nitrite to Four Different Products

We demonstrate for the first time that Pd metal can convert NO₂ ^- to N₂O, N₂, NH₂OH, and NH₃ in a near-neutral electrolyte, with high selectivity to each product attained by adjusting the applied electrode potential. Notably, N₂ and NH₂OH, which are typically difficult to access, emerge as dominant products. Mechanistic investigation combining computational and experimental studies shows that NO₂ ^- electroreduction on Pd is controlled by the applied potential and surface coverage of adsorbed H atoms. The interplay of these two factors gives rise to four distinct reaction microenvironments that are consistent with the experimentally observed product distributions. At positive potentials, the pristine Pd surface favors *NO-*NO coupling and N₂O production, whereas at less positive potentials, the same surface with more reducing power favors N₂. At mildly negative potentials, partial H coverage promotes *NO reduction over coupling and leads to NH₂OH production, while at strongly negative potentials, abundant adsorbed H drives complete reduction to NH₃. Together, these studies provide insight into the rich reductive chemistry at Pd active sites under electrochemical control and enable the rational design of Pd catalysts for environmental remediation and sustainable chemical synthesis.