Revealing the regulation mechanism of carbon dots on Ni(OH)2 for optimizing methanol electrooxidation activity

Abstract

Rational design of Ni-based electrocatalysts for methanol electrooxidation reaction (MOR) and in-depth understanding of their catalytic mechanism remain a challenge. Herein, carbon dots/graphene heterostructure is constructed to load Ni(OH)₂ and the role of carbon dots focuses on regulating distribution and electronic property of Ni(OH)₂. Regulation mechanism of carbon dots on Ni(OH)₂ for optimizing MOR activity are revealed by in-situ Raman, in-situ FTIR, operando electrochemical impedance spectroscopy, X-ray absorption fine structure (XAFS) spectroscopy, and so on. It’s found carbon dots could disperse Ni species and regulate their distribution configuration. Appropriate amount of carbon dots promotes the formation of highly dispersed CDs&Ni(OH)₂ type. Because of strong interaction between Ni(OH)₂ and CDs, coordination environment and local electronic structure of Ni in Ni-CDs/G can be regulated by carbon dots, leading to phase-ratio variation of α-Ni(OH)₂/β‑Ni(OH)₂ and d-band center shift of Ni(OH)₂. For the best Ni-4CDs/G electrocatalyst, more formed α-Ni(OH)₂ lead to d-band center downshift from the E_F level and optimized its adsorption of methanol. Ni-4CDs/G shows the specific activity of 299.2 mA cm⁻² and mass activity of 3756.5 mA mg⁻¹ at peak current. In water splitting test, lower initial overpotential of 140 mV is found in methanol electrolysis than that in water electrolysis. This opens a new door to regulate the metal-based electrocatalysts by CDs and will inspire more people to explore CDs-based materials for electrocatalytic application.