Fig. 5: Mechanism analyses of accelerated HER kinetics.

a Overpotentials at 0.5 A cm−2 for S-NiBDC samples with different S doping amounts. b Polarization curves of S-NiBDC before and after soaking in 0.1 mM Zn(NO3)2 solution and H2O. c, d In-situ ATR-FTIR spectra of S-NiBDC and NiBDC with the potential of 0 to −0.4 V vs. RHE. e, f Polarization curves of S-NiBDC and NiBDC in 1.0 M NaOH H2O solution and 1.0 M NaOD D2O solution. The insets are the KIE values vs. overpotential.