Effect of covalent functionalisation with isocyanates on the electrochemical properties of exfoliated black phosphorus electrodes

Abstract

Abstract This study investigates the covalent functionalisation of few-layer black phosphorus (FLBP) using isocyanates to overcome its inherent susceptibility to oxidation, which limits its application in electrochemical devices. Key synthesis parameters affecting protection efficacy include reactant concentration, ultrasonic irradiation parameters, and solvent selection. While higher reactant concentrations enhance surface coverage, excessive functionalisation impedes interfacial charge transfer. Ultrasonic treatment facilitates optimal reactant-surface interactions, significantly improving electrochemical stability. Comparative solvent analysis indicates acetonitrile outperforms N, N-dimethylformamide in preserving electrochemical performance while enhancing protection against degradation. The research demonstrates that selected isocyanate reactants can effectively passivate the highly nucleophilic three-coordinated phosphorus atoms on FLBP surfaces through the formation of RNHC(O)-P < and RNHC(O)O-P < moieties at reactive surface sites. Electrochemical characterisation reveals that 2xIP(O)(ch)₂_DMF modification provides protection against phosphorus oxidation while maintaining redox functionality. This modification reveals enhanced charge transfer kinetics relative to pristine FLBP or glassy carbon electrodes. The proposed approach widens the electrochemical potential window by eliminating phosphorus oxidation typically observed at 0.65 V while improving charge exchange at the electrode/electrolyte interface. These findings establish a systematic approach for FLBP stabilisation via isocyanate functionalisation, expanding potential applications in energy storage systems, electrocatalysis, and electrochemical sensing technologies.