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Two-dimensional (2D) materials are attracting much attention as emerging photocatalytic water splitting candidates in green and clean energy applications. In this work, we designed four 2D materials, ZnPS 3 , ZnPSe 3 , CdPS 3 and CdPSe 3 , which possess high stability, moderate band-gaps (2.24–3.29 eV), and anisotropic carrier mobilities of 192.26 ─ 676.04 cm2/Vs. Besides, they also have suitable band edges of REDOX at PH = 0, which can simultaneously drive photocatalytic water splitting to produce H 2 and O 2 , and show acceptable free energy for hydrogen evolution reaction (HER) of 0.89–1.20 eV. Moreover, monolayer ZnPSe 3 and CdPSe 3 can deliver strong absorption coefficients (∼105 cm−1) from visible to ultraviolet light. As a result, they have excellent solar-to-hydrogen efficiency of 18.39% and 19.70%, suggesting they are promising photocatalytic candidates for overall water splitting. • 2D ZnPS 3 , ZnPSe 3 , CdPS 3 and CdZnSe 3 have high stability, as well as low cleavage energies of 0.21–0.25 J/m2. • They are indirect semiconductors with band-gaps of 2.24–3.29 eV, and show mobilities of 192.26–676.04 cm2/Vs at 300 K. • They also have suitable REDOX band-edges, which can drive photocatalytic water splitting to produce H 2 and O 2. • Monolayer ZnPSe 3 and CdPSe 3 have excellent solar-to-hydrogen efficiency of 18.39% and 19.70%. [ABSTRACT FROM AUTHOR]

[Display omitted] • Monolayer NiP 2 , PdP 2 and PtP 2 are direct band-gap semiconductors with energy gaps of 0.66 eV, 0.68 eV and 0.40 eV, respectively. • The monolayers simultaneously show ultra-high electron and hole mobilities, up to ∼105 cm2·V−1·s−1. • They exhibit high electrical transport performance with the thermoelectric power factors of 102–103 mW·K−2·m−1 at room temperature. Based on state-of-the-art first principles calculations, we proposed three plana-pentagon monolayers, namely, NiP 2 , PdP 2 and PtP 2. The monolayers are direct band-gap semiconductors with band gaps of 0.66 eV, 0.68 eV and 0.40 eV. In addition, XP 2 (X = Ni, Pd, Pt) simultaneously showed ultrahigh electron and hole mobilities, up to ∼105 cm2·V−1·s−1, resulting in high electrical transport performance with thermoelectric power factors of 102–103 mW·K−2·m−1. Additionally, due to the high group velocities and phonon lifetimes, monolayer XP 2 has thermal conductivities of 21.73, 10.43 and 25.13 Wm−1 K−1 for NiP 2 , PdP 2 and PtP 2 , respectively. As results, the monolayers exhibit favourable ZT values, ranging from 0.08–0.45 at temperatures of 300–700 K. [ABSTRACT FROM AUTHOR]