Delicate design and bottom-up synthesis of hollow nanostructures for oxygen evolution electrocatalysts is a promising way to accelerate the reaction kinetics of overall water splitting. Herein, an efficient and versatile strategy for the controllable preparation of Pd–Cu alloy nanoparticles encapsulated in carbon nanopillar arrays (PD–Cu@HPCN) is developed. Core–shell structured MOF@imidazolium-based ionic polymers (ImIPs) have been prepared and adopted as a template, along with the decomposition of the inner Cu–MOFs when an anion exchange occurs between sodium tetrachloropalladate in solution and bromides in the external ImIP shell. Pd nanoparticles will be highly dispersed in the resulting Pd–Cu@HO-ImIP array, and subsequent topotactic transformation generates Pd–Cu@HNPC. No hazardous reagents or tedious steps are used to remove the inner Cu–MOF templates in contrast to the traditional top-down methods. Remarkably, the Pd–Cu@HPCN catalyst possesses outstanding oxygen evolution reaction (OER) activity, including small overpotential with 10 mA cm–2 at an overpotential of 188 mV, a large double layer capacitance (73.8 mF cm–2), and high stability (20 h). This simple, green, and efficient synthesis methodology represents a new way to design metal alloys for OER electrocatalysts or other electrocatalytic devices.

Rational design of metal–organic frameworks (MOFs) into ultrathin two-dimensional (2D) nanosheets with controllable thickness is significantly attractive but is also a significant challenge. Herein, the authors report, for the first time, the synthesis of ultrathin 2D nickel-based MOF nanosheets with a thickness of only about 2 nm via a ligand-assisted controllable growth strategy, which cannot be acquired from the exfoliation of their bulky counterparts or the conventional hydrothermal method. The correlation between 2D nanosheets and crystal growth preference was demonstrated through a judicious choice of a specific [Ni­(BIP)­(p-BDC)­(H2O)2] n framework (BIP = (3,5-bis­(1-imidazoly)­pyridine), p-H2BDC = terephthalic acid) to underlie the geometry of the resultant morphology. Under the modulation by the dosage of terephthalic acid through a corrosion–dissolution–coordination process, the nanosheets of Ni-MOFs with a controllable thickness can be tuned to 50 and 100 nm. Ultrathin 2D Ni-MOF nanosheet-derived N-doped Ni@carbon exhibits a satisfactory electrocatalytic performance with a small overpotential of 170 mV to achieve a current density of 10 mA cm–2, much outperforming the bulk Ni-MOF and the most reported non-noble-metal oxygen evolution reaction electrocatalysts to date. It is believed that this ligand-assisted controllable growth strategy represents a novel and simple path to prepare high-performance MOF-based electrocatalysts for wide applications.

Metal−organic framework (MOF) ultrathin nanosheets have attracted widespread attention for the oxygen evolution reaction (OER) due to their ultralow thickness and abundant coordinatively unsaturated metal atoms. Here, we first develop an in situ self-dissociation-oriented growth strategy to grow welldefined ultrathin Co-MOF and CoCu-MOF nanosheet arrays on Ni foam. By merely altering the dosage of the ligands, controlled nucleation and orientation growth of MOFs led to confined metal atom growth sites and ultrathin MOF nanosheets with a thickness of only about 2.5 nm. Subsequent pyrolysis treatment in the N 2 atmosphere transforms the ultrathin 2D Co-MOF nanosheets into CoCN and CoCuCN electrocatalysts, which can be directly used as highly active OER electrodes. Remarkably, CoCN and CoCuCN exhibit excellent OER activity at low overpotentials of 231 and 196 mV to deliver a current density of 10 mA cm −2 and long-term stability with negligible decay even after 20 h continuous electrolysis, outperforming most state-of-the-art noble-metal-free and Co-based OER electrocatalysts to date. This study sheds light on the in situ self-dissociation-oriented growth strategy to achieve high-performance ultrathin MOF-based electrocatalysts and provides an advanced pathway to controllably fabricate other types of ultrathin MOF arrays uniformly.