Development of water-stable metal–organic frameworks (MOFs) for promising visible-light-driven photocatalytic water splitting is highly desirable but still challenging. Here we report a novel p-type nickel-based MOF single crystal (Ni-TBAPy-SC) and its exfoliated nanobelts (Ni-TBAPy-NB) that can bear a wide range of pH environment in aqueous solution. Both experimental and theoretical results indicate a feasible electron transfer from the H4TBAPy ligand (light-harvesting center) to the Ni–O cluster node (catalytic center), on which water splitting to produce hydrogen can be efficiently driven free of cocatalyst. Compared to the single crystal, the exfoliated two-dimensional (2D) nanobelts show more efficient charge separation due to its shortened charge transfer distance and remarkably enhanced active surface areas, resulting in 164 times of promoted water reduction activity. The optimal H2 evolution rate on the nanobelt reaches 98 μmol h–1 (ca. 5 mmol h–1 g–1) showing benchmarked apparent quantum efficiency (AQE) of 8.0% at 420 nm among water-stable MOFs photocatalysts.

Layered two-dimensional (2D) lead halide perovskites are a class of quantum well (QW) materials, holding dramatic potentials for optical and optoelectronic applications. However, the thermally activated exciton dissociation into free carriers in 2D perovskites, a key property that determines their optoelectronic performance, was predicted to be weak due to large exciton binding energy (E b , about 100−400 meV). Herein, in contrast to the theoretical prediction, we discover an ultrafast (<1.4 ps) and highly efficient (>80%) internal exciton dissociation in (PEA) 2 (MA) n−1 Pb n I 3n+1 (PEA = C 6 H 5 C 2 H 4 NH 3 + , MA = CH 3 NH 3 + , n = 2−4) 2D perovskites despite the large E b . We demonstrate that the exciton dissociation activity in 2D perovskites is significantly promoted because of the formation of exciton− polarons with considerably reduced exciton binding energy (down to a few tens of millielectronvolts) by the polaronic screening effect. This ultrafast and high-yield exciton dissociation limits the photoluminescence of 2D perovskites but on the other hand well explains their exceptional performance in photovoltaic devices. The finding should represent a common exciton property in the 2D hybrid perovskite family and provide a guideline for their rational applications in light emitting and photovoltaics.