Coordination-Number Engineering as an Independent Design Paradigm for High-Performance 2D Photocatalysts

We propose coordination-number engineering as a composition-independent strategy for designing high-performance photocatalysts. Using isocompositional two-dimensional (2D) ZnTe monolayers, we demonstrate that changing the local coordination from 3-fold in the hexagonal-like (HX) phase to 4-fold in the square-like (SQ) phase markedly enhances photocatalytic performance. The SQ phase exhibits a narrowed band gap of 1.82 eV (compared with 2.59 eV for HX), leading to significantly improved visible-light absorption. Meanwhile, its electron mobility reaches 7.7 × 10⁴ cm² V^-1 s^-1, and the hydrogen evolution reaction thermodynamics is more favorable (ΔG = -0.58 eV), resulting in an increased solar-to-hydrogen conversion efficiency from 14.8% (HX) to 35.67% (SQ). This study highlights coordination-number modulation as a key lever for optimizing photocatalytic activity, providing a general guideline for rational material design.