Embossing Redox-Active Nickel(II) Complexes on Pencil Graphite Electrodes for Frugal Electrocatalytic Hydrogen Production.

Abstract

This work focuses on developing a pencil graphite electrode (PGE) as the working electrode through the electrocatalytic activities of rationally designed coordination-driven electrocatalysts toward sustainable hydrogen production. Upon careful treatment, a normal wooden pencil ($1/INR85) can be transformed into a standard working electrode ($180/INR15000). In this context, the PGE has evolved as the working electrode with rationally designed nickel(II) complexes Ni-L^Me and Ni-L^Ph obtained through one-pot synthesis between alkyl-thiosemicarbazide and acenaphthylene-1,2-dione and nickel(II) acetate. X-ray crystallography analysis reveals that both the nickel complexes adopt an isostructural square planar coordination geometry. The PGE/Ni-L^Me and PGE/Ni-L^Ph in aqueous 0.5 M H₂SO₄ rendered an overpotential of about 0.48 and 0.41 V vs. RHE with a Tafel slope of 149 and 101 mV per decade, respectively. Chronopotentiometry and constant potential electrolysis ensure excellent durability and electrocatalytic hydrogen production with 95% and 98% faradaic efficiency, respectively, for Ni-L^Me and Ni-L^Ph. Crystal engineering approaches attribute the higher electrocatalytic activities of Ni-L^Ph over Ni-L^Me to its higher surface area and planarity. The high propensity of strong stacking interactions between the extensive π-electronic conjugated network of PGE and square planar nickel complexes leads to a perfect synergism and facilitates rapid electron transport with high electrocatalytic efficiency.