Harnessing Adsorbate-Adsorbate Interaction to Activate C-N Bond for Exceptional Photoelectrochemical Urea Oxidation

The photoelectrochemical (PEC) urea oxidation reaction (UOR) presents a promising half-reaction for green hydrogen production, but the stable resonance structure of the urea molecule results in sluggish kinetics for breaking the C-N bond. Herein, we realize the record PEC UOR performance on a NiO-modified n-Si photoanode (NiO@Ni/n-Si) by harnessing the adsorbate-adsorbate interaction. We quantificationally unveil a dependence of the UOR activation barrier on the coverage of photogenerated surface high-valent Ni-oxo species (Ni^IV=O) by employing operando PEC spectroscopic measurements and theoretical simulations. The strong attraction between Ni^IV=O and adsorbed urea facilitates their N-O coupling while weakening the C-N bonding within urea, manifesting as the decreased UOR activation energy from 0.74 to 0.41 eV when the surface coverage of Ni^IV=O is enhanced from zero to full, corresponding to more than two orders of magnitude enhancement for the UOR rate. Furthermore, an industrial-grade photocurrent density of 100 mA cm^-2 is achieved at a potential as low as 1.08 V_RHE by stimulating the Ni^IV=O accumulation under 10 Suns, which is 300 mV lower than the potential required for most reported electrochemical counterparts. This work opens new prospects for achieving high-performance PEC urea oxidation via adsorbate-adsorbate interaction.