SiCP₄ Monolayer with a Direct Band Gap and High Carrier Mobility for Photocatalytic Water Splitting

Photocatalytic water splitting is a promising method that uses sunlight to generate hydrogen from water to provide clean and renewable energy resources. Two-dimensional materials with abundant active sites are ideal candidates for achieving this goal; however, few of the known ones can meet the rigorous requirement of photocatalytic water splitting. By using first-principles swarm-intelligence search calculations, we have successfully identified two new semiconducting SiCP₂ and SiCP₄ monolayers. Their band-edge heights evidently straddle the redox potentials of water. For the more prominent SiCP₄ monolayer, additional external biases of 0.32 V for water oxidation and 0.03 V for the hydrogen reduction half-reaction would be enough to drive its reaction sequences at pH 0, and it can spontaneously proceed to the water oxidation half-reaction in a neutral solution. Interestingly, the excellent optical absorbance ability (∼10⁴ cm^-1) and high carrier mobility (∼10⁵ cm² V^-1 s^-1) of SiCP₂ and SiCP₄ facilitate the utilization of sunlight and the fast transportation of photogenerated carriers. All of these properties make SiCP₂ and SiCP₄ monolayers promising candidates for applications in photocatalytic water splitting.