Green synthesis of hybrid papain/Ni3(PO4)2 rods electrocatalyst for enhanced oxygen evolution reaction

Abstract

Hydrogen production using electrocatalytic water splitting provides encouraging innovations for enduring and clean energy generation as an option in contrast to traditional energy sources. Improvement in exceptionally dynamic electrocatalysts is of tremendous interest for work on the proficiency of gas generation, which has been emphatically blocked because of the sluggish kinetics of the oxygen evolution reaction (OER). We have synthesized a noble rod-shaped papain/Ni₃(PO₄)₂ catalyst, which was further explored for electrocatalytic OER activity. An environmentally benign approach was applied to prepare binary papain/Ni₃(PO₄)₂ in the presence of papain obtained from green papaya fruit. The yield of Ni₃(PO₄)₂ rod structures could be controlled by varying the amount of papain extract during reaction conditions. The morphology and structural properties of the biogenic papain/Ni₃(PO₄)₂ electrocatalyst were investigated with various microscopic and spectroscopic techniques, for example, FE-SEM, XRD, XPS, and FTIR. To show how such a papain/Ni₃(PO₄)₂ hybrid structure could deliver more remarkable electrocatalytic OER activity, we inspected the correlation between catalytic demonstrations of the papain/Ni₃(PO₄)₂ catalyst and its constituents, and the role of papain on its own was studied during the OER process. A biosynthesised papain/Ni₃(PO₄)₂ catalyst exhibits excellent electrochemical OER performance with the smallest overpotentials of 217 mV, 319 mV and 431 mV in alkaline, neutral and acidic conditions, respectively, at 10 mA cm⁻² current density. Transport of ions and electrons is also assisted by the long peptide backbone present in papain, which plays an important role in boosting OER activity. Our results reveal that papain/Ni₃(PO₄)₂ shows better electrocatalytic OER execution along with cyclic stability compared to its different counterparts, owing to synergism-assisted enhancement by several amino acids from papain with metal ions in Ni₃(PO₄)₂.