Fig. 4: Electron transport in hBN/NiFeO_xH_y heterostructures.

a and b are in situ Raman spectra of hBN/NiFeO_xH_y and NiFeO_xH_y electrodes at various potentials versus RHE, respectively. The blue and black dashed lines mark the characteristic peaks for Ni²⁺ (at 450 cm⁻¹ and 540 cm⁻¹) and Ni^3+δ (at 470 cm⁻¹ and 550 cm⁻¹), respectively^55,56,57.