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Engineering nanostructured spinel ferrites by co-substitution for total water electrolysis by preferential exposure of metal cations on the surface

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Abstract

Single phasic magnetite samples co-substituted with cobalt and nickel, with the formula CoxNi(0.4−x)FeII0.6FeIII2O4 (x = 0, 0.1, 0.2, 0.3, and 0.4) were synthesized in the nanoregime via a co-precipitation technique. Being an inverse spinel, magnetite will preferentially expose the octahedral sites and make metal cations available on the surface, which will play a conducive role in both hydrogen evolution (HER) and oxygen evolution (OER) reactions. We demonstrate that the partial substitution of Fe2+ (either by Ni2+ or Co2+ ions) on the octahedral sites of the inverse spinel structure of CoxNi(0.4−x)FeII0.6FeIII2O4 significantly enhance the bifunctional electrocatalytic activity of the magnetite samples in an alkaline medium. The spinel ferrite with the formula Co0.2Ni0.2FeII0.6FeIII2O4 exhibits outstanding bifunctional electrocatalytic activity in 1 M KOH with the lowest onset overpotential (ƞOER = 190 and ƞHER = 200 mV), small overpotential at η10 (OER = 270 mV and HER = 275 mV), excellent kinetics (Tafel slopes, bOER = 44 mV dec−1 and bHER = 99 mV dec−1), and high durability (>10 h). Furthermore, Co0.2Ni0.2FeII0.6FeIII2O4 can serve as both cathode and anode for the overall water-splitting reaction, and delivered a current density of 10 mA cm−2 at a very low cell voltage of 1.72 V with excellent stability (>10 h at 10 mA cm−2). Thus, this work provides a lucid approach to engineer a highly efficient non-noble transition metal-based electrocatalyst for renewable energy applications via simple micro-structural and surface engineering.

Graphical abstract: Engineering nanostructured spinel ferrites by co-substitution for total water electrolysis by preferential exposure of metal cations on the surface

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Supplementary files

Article information


Submitted
08 Apr 2020
Accepted
20 May 2020
First published
20 May 2020

Sustainable Energy Fuels, 2020, Advance Article
Article type
Paper

Engineering nanostructured spinel ferrites by co-substitution for total water electrolysis by preferential exposure of metal cations on the surface

A. V. N., P. K. Rastogi, T. S., V. S., S. Shaji, R. R. V., M. A. Garza-Navarro, S. Thomas, T. N. Narayanan and M. R. Anantharaman, Sustainable Energy Fuels, 2020, Advance Article , DOI: 10.1039/D0SE00561D

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