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 (NiIV=O) by employing operando PEC spectroscopic measurements and theoretical simulations. The strong attraction between NiIV=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 NiIV=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 VRHE by stimulating the NiIV=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.