Investigation on the intrinsic catalytic activity of structurally diverse polycrystalline nickel microstructures such as porous nickel sheets (PNS), porous folded/curled nickel structures (PFNS) and porous nickel balls (PNB) revealed the surface bounded electrocatalytic activities within an alkaline reaction environment for water oxidation. Nickel microstructures were grown via template/surfactant-free, single step solution combustion technique in air atmosphere. The distinct morphologies (porous nickel sheets, porous folded/curled nickel structures and porous nickel balls) were achieved through changing the quantity of HNO3 in the reaction mixture. The physicochemical characterisations were done with XRD, FESEM, EDS and XPS. Microscopic studies revealed the growth of nickel grains with numerous macro pores forming microstructures in distinct morphologies. The O ls spectra of XPS studies revealed the presence of O−/O2− sites and Ni 2p spectra were distinguished between the formation of Ni0/Ni2+/Ni3+ states, implied the existence of surface oxide with plenty of defects. The synergistic effect results from the formation of microscopic porous architectures with defect rich surface oxide on the electrochemical behaviour and OER activity of PNS, PFNS and PNB were discussed with electrochemical techniques such as CV, LSV, EIS and CP. The OER kinetics in terms of relatively low value of overpotential at 10 mA cm−2 and Tafel slope along with high specific activity of PNS/GCE with respect to PFNS/GCE and PNB/GCE were attributed to the combined effect of increase in electrochemical surface area, high roughness factor and fast charge transfer kinetics. The better electrochemical performance and OER activities of porous nickel sheets in comparison with folded/curled nickel structures and nickel balls is contributed to the unique 2D porous architecture with plenty of oxygen vacancies. This structure not only expose more surface for the formation of passive oxide layer in an alkaline reaction environment but also exhibit facile charge transport properties, causes the generation of numerous surface-active sites for electrocatalytic water oxidation. The outcome of our work gives new insights on the surface electrochemistry of polycrystalline nickel, enables micro-structuring as a prospective strategy towards the optimization of electrocatalysts as anode material for alkaline water oxidation.
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