This review scrutinizes recent progress in PEMWE system including mechanisms, the correlation among structure-composition–performance, manufacturing, system design and operation protocols. The challenges and perspectives for applications are proposed.

In this work, surfactant-free atomically ultrathin Rh nanosheet nanoassemblies (Rh NNs) are synthesized and used for the first time as an effective electrocatalyst in the nitrogen reduction reaction (NRR) at ambient temperature and pressure. The inorganic polymer RhCl₃–K₃Co(CN)₆ cyanogel plays an important role in the generation of ultrathin Rh nanosheets with a clean surface. Due to their unique ultrathin two-dimensional nanosheet structure (ca. 1 nm) with a high specific surface area and modified electronic structure, the surfactant-free Rh NNs demonstrate an excellent catalytic activity for the NRR with a high production yield (NH₃: 23.88 μg h⁻¹ mg_cat ⁻¹) and favorable selectivity (no N₂H₄ generation) at low potential (−0.2 V vs. RHE), outperforming most of the current electrocatalysts reported for the NRR. Except the contribution to the efficient NRR electrocatalysis, this synthesis strategy would provide some new insights into the preparation of ultrathin precious metal nanosheets for energy related applications.

The 2D conductive metal–organic frameworks (MOFs) are expected to be an ideal electrocatalyst due to their high utilization of metal atoms. Exploring a new conjugated ligand with extra active metallic center can further boost the structural advantages of conductive MOFs. In this work, hexaiminohexaazatrinaphthalene (HAHATN) is employed as a conjugated ligand to construct bimetallic sited conductive MOFs (M2₃(M1₃∙HAHATN)₂) with an extra M–N₂ moiety. Density functional theory (DFT) calculations demonstrate that the 2D conjugated framework renders M2₃(M1₃∙HAHATN)₂ a high electric conductivity with narrow bandgap (0.19 eV) for electron transfer and a favorable in‐plane porous structure (2.7 nm) for mass transfer. Moreover, the metal atom at the extra M–N₂ moiety has a higher unsaturation degree than that at M–N₄ linkage, resulting in a stronger ability to donate electrons for enhancing electroactivity. These characteristics endow the new conductive MOFs with an enhanced electroactivity for hydrogen evolution reaction (HER) electrocatalysis. Among the series of M2₃(M1₃∙HAHATN)₂ MOF, Ni₃(Ni₃∙HAHATN)₂ nanosheets with the optimal structure exhibit a small overpotential of 115 mV at 10 mA cm⁻², low Tafel slope of (45.6 mV dec⁻¹), and promising electrocatalytic stability for HER. This work provides an effective strategy for designing conductive MOFs with a favorable structure for electrocatalysis.