Constructing bimetallic conjugated coordination polymers as efficient electrocatalysts for water splitting

Abstract

With the advancement of non-precious metal electrocatalysts, coordination polymers have emerged as a promising alternative to precious metal nanomaterials for hydrogen evolution reactions (HERs) and oxygen evolution reactions (OERs), due to their diverse structures and superior cost-effectiveness. However, challenges remain in precisely modifying the electronic structure at the molecular level to improve the HER and OER activities of coordination polymers. In the field of energy storage, π-d conjugated coordination polymers (CCPs) have been deeply researched due to their designability and outstanding electrical conductivity. In this study, a series of bimetallic CCPs, Co_xNi_1−x–DHBQs (x =0, 1/2, 1/3, 1/4, 1/5, and 1 and H₂DHBQ = 2,5-dihydroxycyclohex-2,5-diene-1,4-dione), were synthesized via simple methods. By changing the proportions of cobalt and nickel metal centers, Co_1/3Ni_2/3–DHBQ exhibited an overpotential of only 270 mV and a Tafel slope of 62 mV dec⁻¹ at a current density of 10 mA cm⁻² during the oxygen evolution reaction (OER) test. During the hydrogen evolution reaction (HER) evaluation, the best-performing Co_1/3Ni_2/3–DHBQ showed an overpotential of merely 177 mV and a Tafel slope of 119 mV per decade at the identical current density. In addition, using Co_1/3Ni_2/3–DHBQ for both electrodes in a water electrolysis system resulted in a remarkably low cell voltage of 1.55 V at a current density of 10 mA cm⁻². Notably, after 70 hours of stability testing, no significant performance degradation was observed. The prepared catalyst exhibits excellent electrocatalytic properties, which stem from the synergistic influence of cobalt and nickel metal centers embedded in the conjugated coordination polymer matrix, providing abundant accessible active sites, rapid ion/electron transport, and efficient O₂/H₂ release channels.