Size Controllable Metal Nanoparticles Anchored on Nitrogen Doped Carbon for Electrocatalytic Energy Conversion

Metal nanoparticles (NPs) are an important class of materials for electrocatalysis. Synthesis of metal NPs with uniform particle size below 10 nm without a capping agent is challenging due to the tendency of particle aggregation to minimize surface energy. Here we demonstrate that pyrolysis of a metal-TCNQ (TCNQ⁻=tetracyanoquinodimethane radical anion) compound can produce metal NPs with controllable particle sizes anchored on nitrogen doped carbon (denoted as MetalNC). NiNC and CoNC derived from Ni-TCNQ and Co-TCNQ with Ni and Co particle sizes below 10 nm were successfully prepared. NiNC, with a particle size of 8.8 nm, showed excellent catalytic activity for hydrogen evolution in an alkaline medium, reaching a catalytic current density of 10 mA cm⁻² at an overpotential of 230 mV. CoNC, with a particle size of 1.8 nm, exhibited the capability of producing syngas by electrocatalytic CO₂ reduction over a wide potential range in an acetonitrile medium containing 0.3 M H₂O. An artificial photosynthesis system based on CoNC achieved faradaic efficiencies of over 70 % for production of syngas and 22 % for formate. This work demonstrates a general strategy to synthesize size controllable metal NPs supported on carbon materials for electrocatalytic energy conversion.