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[Display omitted] • Based on the USPEX screening more stable SiCP 4 allotropes was obtained. • A high carrier mobility of 106 cm2 V−1 s−1 is observed for SiCP 4 allotrope. • The maximum η S T H ′ and η S T F ′ of SiCP 4 allotrope can reach 21.89% and 23.90% • Two SiCP 4 allotropes can trigger HER spontaneously. • SiCP 4 allotropes have the potential to reduce CO 2 to CH 4 or HCOOH. Two-dimensional metal-free photocatalysts are catching the attention of researchers. Here, we present several allotrope SiCP 4 monolayers with high stability, high carrier mobility, and excellent photocatalytic performance. Using a searching method based on the universal structure predictor evolutionary xtallography, together with assessing the energy and thermodynamic stabilities, and matching the potentials of band edges with the photocatalytic conditions for achieving overall water splitting, we successfully identify 5 highly favorable configurations (including the previously reported one) from a pool of 1056 allotrope SiCP 4 monolayers. The results show that the largest solar-to-hydrogen efficiency of the considered monolayers can reach 21.89 %, while a high mobility of 2.7677 × 105 cm2 V−1 s−1 is observed, both are superior to those of the previously reported one. The Gibbs free energies for hydrogen or oxygen evolutions, and CO 2 reduction reactions indicate they are thermodynamically feasible. Moreover, the hydrogen evolution reaction can proceed spontaneously with two allotrope SiCP 4 monolayers. Therefore, the newfound allotrope SiCP 4 monolayers are expected to have potential applications in the field of photocatalytic water splitting for hydrogen generation and carbon dioxide reduction. [ABSTRACT FROM AUTHOR]