The effect of carbon quantum dots on the electrocatalytic hydrogen evolution reaction of manganese–nickel phosphide nanosheets

Abstract

Transition-metal phosphides (TMPs) are good electrocatalysts for the hydrogen evolution reaction (HER) due to their high catalytic efficiency and low cost. Carbon quantum dots (CQDs) deposited on top of TMPs could make them even better for the HER by increasing the surface area and the number of active sites. Here we report a method to synthesize CQD-modified manganese–nickel phosphide (CQDs/Mn_xNi_5−xP₄) for efficient and stable HER activity using inexpensive raw materials. In 0.5 M H₂SO₄, CQDs/Mn_xNi_5−xP₄ requires a low overpotential of only 31 mV to achieve a current density of 10 mA cm⁻², as well as having a low Tafel slope of 41.0 mV dec⁻¹, a large exchange current density of 1.753 mA cm⁻², and good stability, making it better than most reported transition-metal-based catalysts. Moreover, CQDs/Mn_xNi_5−xP₄ also displays high activity and stability in alkaline solution, revealing that the ancillary role played by CQDs could be beneficial under both acidic and alkaline conditions. Based on our results, we believe that CQDs have great potential to be applied to other materials with various morphologies and structures for designing high-performance HER catalysts.