Co-Ni Bimetallic Zeolitic Imidazolate Frameworks Supported on Carbon Cloth as Free-Standing Electrode for Highly Efficient Oxygen Evolution

Abstract

In recent years, hydrogen production has driving a growing focus in the researches of clean energy, particularly the significance of the oxygen evolution reaction (OER) in water splitting. However, the most fascinating OER catalysts of noble metals are hindered by high cost, limited resources, and poor stability. Therefore, the development of low-cost, efficient, stable, and replaceable electrocatalysts is of utmost importance to accelerate the rate of OER in water splitting and realizing renewable, clean, and large-scale energy conversion technologies. Bimetallic and polymetallic electrocatalysts have shown enormous potential, as each metal component can independently or synergistically enhance the electrocatalytic activity. However, during the catalytic process, some metal ions may leach, leading to changes in the catalyst surface morphology and a significant reduction in activity and stability. Extensive research efforts are being devoted to effectively address the challenges associated with metal dissolution. In this study, we have developed a simple method for preparing bimetallic CoNi zeolitic imidazolate framework (CoNi-ZIF) by removing guest molecules through low-temperature pyrolysis and firmly loading CoNi-ZIF nanosheets onto carbon cloth (CoNi-ZIF-CC-200). The resulting free-standing electrodes have several advantages, including independence from adhesives and avoidance of ineffective surface area, thereby significantly improving the catalytic activity and mass transfer efficiency of the catalyst. The electrochemical test results indicate that the CoNi-ZIF-CC-200 free-standing electrode exhibits good electrochemical activity and stability during the OER process. Specifically, the CoNi-ZIF-CC-200 electrode demonstrates a low overpotential of 255 mV under a current density of 10 mA∙cm⁻² and maintains stable operation for over 10 h during potentiostatic measurements. Additionally, the water splitting system consisting of the CoNi-ZIF-CC-200 free-standing electrode as the anode and Pt/C as the cathode exhibits excellent stability. The research highlights the use of a low-temperature pyrolysis strategy for firmly loading bimetallic ZIF-L nanosheets onto carbon cloth. This approach results in well-arranged nanosheet arrays, which prevent ineffective surface area and improve mass transfer efficiency during the OER process. Moreover, the removal of guest molecules at low temperatures leads to the formation of Co/Ni oxides, which play a crucial role in catalyzing the OER. The prepared free-standing electrode based on bimetallic ZIF and oxide demonstrates excellent electrochemical activity and stability in both three-electrode and two-electrode water splitting systems using 1 mol∙L⁻¹ KOH as the electrolyte. It is strongly believed that CoNi-ZIF-CC-200 holds great promise for future applications in large-scale electrocatalytic hydrogen production systems.

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