(a) STEM EDS mapping images of PdCu-H nanoparticles. (b, c) The ${\text{FE}}_{{\text{NH}}_{\text{3}}}$ values and NH₃ yield rates of PdCu-H, PdCu-P, and commercial Pd-P, collected under different potentials. (d) The relationships between ${\text{FE}}_{{\text{NH}}_{\text{3}}}$ and rotation rates over PdCu-H, PdCu-P, and Pd-P. (e) LSV curves and summarized relationships between current densities and the square root of scan rates for the NO₃⁻RR electrocatalysis over PdCu-H. (f) Schematic illustrations for selective NO₃⁻RR electrocatalysis over PdCu-P. Adapted from Ref. [32]. Copyright 2023, Wiley-VCH GmbH. (g, h) TEM images of Co₃O₄ and R-Co₃S₄. (i) The NH₄⁺ yield rate and FE on Co₃O₄ at varying potentials. (j) The corresponding NH₄⁺ yield and FE at different potentials for R-Co₃O₄ catalyst in the electrolyte of 0.1 M KOH with 1000 ppm KNO₃ for 1 h under different potentials. Error bars correspond to the standard deviations of three independent measurements. (k) Reaction pathway for nitrate reduction to ammonia on the R-Co₃O₄ catalyst. (l) Gibbs free energy diagrams at U = 0.0 V and atomic configurations of key adsorbed intermediates for NO₃RR on the R-Co₃O₄ catalyst and Co₃O₄ catalyst, in which the light blue, red, white, and dark blue represent Co, O, H, and N, respectively. Adapted from Ref. [33]. Copyright 2023, Elsevier.