Efficient electrocatalytic water oxidation by using the hierarchical 1D/2D structural nanohybrid of CoCu-based zeolitic imidazolate framework nanosheets and graphdiyne nanowires

Abstract A novel catalyst comprising the one-dimensional (1D)/two-dimensional (2D) nanostructural nanohybrid of CoCu-based zeolitic imidazolate framework nanosheets (CoCu-ZIF NSs) and graphdiyne (GDY) nanowires (denoted as CoCu-ZIF@GDY) was prepared using the strategy of covalent-organic framework (COF) on metal-organic framework (MOF). The prepared CoCu-ZIF@GDY was further explored as electrocatalyst for oxygen evolution reaction (OER) and overall water splitting in alkaline solution. The CoCu-ZIF NSs were synthesized by a two-step method, including the preparation of bulk CoCu-ZIF nanoparticles and the formation of CoCu-ZIF NSs by adding excess Co2+ and Cu2+ ions. Different from routine bulk ZIF nanomaterials, the obtained CoCu-ZIF NSs exhibited an ultrathin 2D structure and comprised a large amount of CoCu2O4 spinel. The GDY COF demonstrated a highly-conjugated structure, strong adsorption ability toward oxygen, nanowire shape, and a large amount of carbon dots. All of these features endowed the CoCu-ZIF NSs and GDY nanowires with excellent electrochemical conductivity, fast electron-transport ability, and high number of exposed active sites, further leading to the synergistic effect and the direct binding between CoCu-ZIF and GDY. The CoCu-ZIF@GDY nanohybrid further displayed superior OER performance over other transition-metal- and carbon-nanomaterial-based catalysts, giving an extremely low overpotential of 250 mV to acquire a current density of 10 mA cm−2. When used as the electrolyzer catalyst for two-electrode overall water splitting, it also gave a low overpotential of 290 mV at a current density of 10 mA cm−2 and outstanding stability possibly due to the ability of the GDY network to prevent CoCu-ZIF from corroding in alkaline solution. Overall, this work provided a promising strategy for the exploration of electrocatalysts based on bimetallic MOFs and COFs for clean energy.