Surface coordination chemistry and engineering of earth-abundant metal-based nanocomposites and frameworks for green hydrogen production through water splitting process

Official URL: https://dx.doi.org/10.1016/j.mser.2026.101250

The escalating climate crisis demands urgent transition to sustainable energy carriers, with green hydrogen produced via water splitting emerging as a crossable solution. However, the widespread deployment of this technology remains constrained by the prohibitive cost and scarcity of noble metal catalysts (Pt, Ir, Ru) that currently dominate the field. This review synthesizes recent advances in surface coordination chemistry for three earth-abundant platforms, MOFs, graphene-supported nanoparticles, and single-atom catalysts (SACs) for green hydrogen production via photocatalytic, photoelectrocatalytic, and PV-EC water splitting, elucidating how atomic-scale coordination governs catalytic performance. To unify these platforms, the review introduces the Coordination-Interface-Reactivity (CIR) Trio; a framework where optimal performance emerges from the synergistic optimization of atomic-scale coordination, nanoscale interfacial coupling, and meso-to-macroscale reactive site architecture. The review demonstrates that coordination modulation and facet engineering enable precise control over crystal plane exposure, with a critical distinction between three hierarchical levels of performance metrics that must not be directly compared. At the intrinsic catalytic level (Tier 1), DFT-calculated ΔGH* values approaching the ideal 0 eV (e.g., −0.08 eV for Co-P₄ SACs) and turnover frequencies of 0.246 s⁻1 demonstrate that coordination engineering can achieve near-optimal binding energetics independent of reactor design. Within this tier, single-atom catalysts represent the apex of atomic efficiency, wherein coordination number variation (e.g., FeN4 vs. FeN5 vs. FeN6) and heteroatom doping (Co-P4 configurations achieved ΔGH* = −0.08 eV) enable near-thermoneutral hydrogen adsorption, while the electronic metal-support interaction (EMSI) emerges as a unifying design parameter governing both activity and stability through orbital hybridization and charge redistribution. At the half-cell or electrode level (Tier 2), coordination modulation and facet engineering enable precise control over crystal plane exposure, with heterobimetallic Cu-Zr/Hf MOFs exposing {101} and {011} facets achieved unprecedented photocatalytic hydrogen evolution rates approaching 50,000 μmol g⁻1 h⁻1. Furthermore, the strategic manipulation of MSI through π-d orbital hybridization in graphene-supported systems, exemplified by {110}-dominated rhombic Cu2O and {111}-exposed Co3O4 polyhedrons, establishes direct correlations between coordination geometry and catalytic activity, yielding mass-normalized HER rates exceeding 100,000 μmol g⁻1 h⁻1 (Cu/TiO2 SAC), apparent quantum yields (AQY) of 56% at 365 nm, and photocurrent densities of 7.1 mA cm⁻2 (textured Fe2O3). These metrics reflect performance under controlled laboratory conditions but depend on catalyst loading and electrode geometry. At the device or system level (Tier 3), integration of these architectures into photocatalytic, photoelectrocatalytic, and PV-EC systems has yielded solar-to-hydrogen efficiencies approaching 1% (Co-P SAC) in pure water splitting, photocurrent densities exceeding 5 mA cm─2, and PV-EC tandems surpassing 20% efficiency at kilowatt scales. The analysis identifies distinct optimization patterns, critical bottlenecks, and vast unexplored design space, including the combination of facet-controlled MOFs with single-atom decoration. Scale-up and manufacturing constraints are consolidated into a dedicated section addressing precursor cost, batch-to-batch consistency, toxicity, and compatibility with realistic operating conditions.