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

This study transforms a simple pencil into a cost-effective graphite electrode, enhanced with nickel(II) complexes Ni-L^Me and Ni-L^Ph for efficient hydrogen production. Ni-L^Ph shows superior electrocatalytic activity and durability, driven by strong π–π interactions and planar structure, enabling rapid electron transfer and high faradaic efficiency, promising sustainable and affordable green energy solutions.

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.

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