Fig. 4. Proposed lattice hydrogen transfer mechanism.

a Model diagrams for positive and reverse validation of isotope-labeled lattice hydrogen transfer in the NIRR process. b Isotope labeled lattice hydrogen transfer in NIRR process for TiH_1.97 (positive validation) and (c) TiD_1.97 (reverse validation). d the double layer capacitance in the electrolyte with and without NO₃⁻ at a potential range without Faraday reaction. e LSV curves of titanium hydride with or without TBA (without iR compensation). f SKIE values under different applied potentials. Inset of Fig. 4f were LSV curves of titanium hydride in different proportions of mixed D₂O and H₂O solution, n = D₂O/ [D₂O + H₂O] (without iR compensation). g DMPO-involved ESR spectra of the titanium hydride and Ti FP under different electrolysis conditions. h The Nyquist plots (without iR compensation) and (i) The Tafel slope (without iR compensation). j Schematic of the reaction mechanism.