In situ precipitated NiCo nanoparticles synergize with metaborate to promote hydrogen evolution and couple with urea oxidation to reduce overall water splitting potential

Abstract

A novel NiCo nanoparticles anchored on Ni(Co)(BO2)2 are constructed via a simple redox reaction of NiCo LDH (layered double hydroxide) with NaBH4 which method avoids the Ni foam deformation caused by high temperature reduction or pyrolysis. The experimental and DFT (density functional theory) investigation reveal metaborate (Ni(Co)(BO2)2) exhibits a stronger water adsorption capacity than that conventional metal LDH, which is conducive to the occurrence of hydrogen adsorption in the next step, while NiCo (ΔGH* is closer to 0) is a more suitable hydrogen reaction site than Ni or Co, this synergistic effect of the two substances greatly promotes Volmer step for HER (hydrogen evolution reaction), thereby fundamentally improving HER. The existence of Co0 helps to generate more Ni0, and Co plays an electronic auxiliary role. The Ni0(Co0)-Ni(Co)(BO2)2/NF catalyst possesses small charge transfer resistance, large electrochemical surface area and good hydrophilicity. The Ni0(Co0)-Ni(Co)(BO2)2/NF catalyst exhibits a great application prospect with an overpotential of only 25 mV at a current density of 10 mA cm−2. Even at a large current density of 100 mA cm−2, the overpotential is 107 mV. At a current density of 10 mA cm−2, the voltages of OER (oxygen evolution reaction) and UOR (urea oxidation reaction) are 1.561 V (vs. RHE) and 1.353 V, respectively. Using Ni0(Co0)-Ni(Co)(BO2)2/NF as a bifunctional catalyst for HER and UOR, only 1.47 V can drive a current density of 10 mA cm−2. It is shown that the catalyst will greatly reduce energy consumption and decompose urea when coupling HER and UOR.