Surface hydrophobicity induced electrochemical nitrogen reduction reaction: A substrate-dependent case study on Cu foam versus Cu foil

Hydrophobic surface modification is an emerging concept for electrochemical gas-phase reactions like nitrogen reduction reaction to ammonia as the restricted surface wettability helps to surpass the competitive hydrogen evolution reaction. However, the extensive studies on this strategy lack a discussion on the influence of substrates on the stability of the hydrophobic coating. The present work summarizes a case study on the substrate-dependent electrochemical behaviour of the alkanethiol-coated flattened Cu foil and porous dendritic Cu foam surfaces. NRR studies reveal that the porous dendritic architecture with electrified tips and the hydrophobic coating-induced gas diffusion layer proved to be beneficial for NRR activity in Cu foam-SH. However, for a prolonged experimental hour, the flattened surface of the Cu foil could better hold the hydrophobic coating. The results corresponded with water contact angle as well as double layer capacitance measurements and a detailed X-ray photoelectron spectroscopy study. It is supposed that the prolonged exposure to applied potential alters the polarization of the Cu dendritic tips and weakens the Cu–S bond, loosening the alkanethiol layer over Cu foam.

Graphical abstract

Hydrophobic Cu substrates facilitate electrochemical nitrogen reduction reactions owing to the better N₂ diffusion and trapping underneath the hydrophobic coating. While the NRR activity gets accelerated at the electrified dendritic tips of Cu foam, the steady hydrophobic layer over the flattened Cu foil surface ascertains long-term use of the material.