Enhancing Hydrogen Evolution Reaction through the Improved Mass Transfer and Charge Transfer by Bimetal Nodes.

Abstract

The high cost of hydrogen production by water electrolysis severely challenges its commercial application. It is highly desirable to develop efficient electrocatalysts and innovative electrolytic cells. Introducing additional metal nodes to form bimetallic metal-organic framework (MOF) is a simple, feasible strategy to overcome the poor electrocatalytic performance of single-metal MOF. In this study, the hydrothermal method is used to synthesize bimetallic Ni_xCo_y-BTC. It is found that for hydrogen evolution reaction (HER), Ni_0.8Co_0.2-BTC merely requires a potential of -0.203 V (vs reverse hydrogen electrode, RHE) to achieve 10 mA cm^-2, which is significantly lower than that of Ni-BTC (-0.341 V vs RHE). Notably, electrochemical impedance spectroscopy (EIS) and distribution of relaxation time (DRT) analysis indicate that Ni_xCo_y-BTC has improved charge transfer and mass transfer process, compared with Ni-BTC. Electron paramagnetic resonance (EPR) confirms that Ni_0.8Co_0.2-BTC has more unpaired electrons than Ni-BTC. Density functional theory (DFT) calculations show that compared with Ni-BTC, Ni_xCo_y-BTC is more thermodynamically favorable for the adsorption of H⁺, OH^-, and H₂O. It demonstrates that the change of mass transfer caused by bimetallic nodes and the delicate variation of MOF surface play an important role in the electrochemical process. Moreover, a novel electrolytic cell was developed using a methanol oxidation reaction (MOR) to replace oxygen evolution reaction (OER). In this MOR-based electrolytic cell, a current density of 50 mA cm^-2 can be achieved at only a cell voltage of 1.85 V, which is lower than the 2.22 V of OER-based electrolytic cell, suggesting that 16.7% electric energy can be saved. At the same time, the Faraday efficiency (FE, 98.2%) of the MOR-based cell is higher than that (94.5%) of the OER-based cell. This research offers a promising strategy for low-cost hydrogen production.