Abstract
The design of efficient electrocatalysts for oxygen evolution reaction (OER) is an essential task in developing sustainable water splitting technology for the production of hydrogen. In this work, manganese cobalt spinel oxides with a general formula of MnxCo3-xO4 (x = 0, 0.5, 1, 1.5, 2) were synthesised via a soft chemistry method. Non-equilibrium mixed powder compositions were produced, resulting in high electrocatalytic activity. The oxygen evolution reaction was evaluated in an alkaline medium (1 M KOH). It was shown that the addition of Mn (up to x ≤ 1) to the cubic Co3O4 phase results in an increase of the electrocatalytic performance. The lowest overpotential was obtained for the composition designated as MnCo2O4, which exhibited a dual-phase structure (∼30% Co3O4 + 70% Mn1.4Co1.6O4): the benchmark current density of 10 mA cm−2 was achieved at the relatively low overpotential of 327 mV. The corresponding Tafel slope was determined to be ∼79 mV dec−1. Stabilities of the electrodes were tested for 25 h, showing degradation of the MnCo2O4 powder, but no degradation, or even a slight activation for other spinels.
Highlights
Among different hydrogen production methods, water electrolysis seems to be a viable process to provide clean hydrogen [1,2], especially when coupled with renewable electricity production
The results indicate that the lowest overpotential (h) at 10 mA cmÀ2 of 289 mV was exhibited by IrO2 but its performance weakened at higher overpotentials compared to the other synthesised spinels
The powders were analysed for their surface area, chemical and phase composition, and their electrocatalytic properties towards oxygen evolution reaction
Summary
Among different hydrogen production methods, water electrolysis seems to be a viable process to provide clean hydrogen [1,2], especially when coupled with renewable electricity production. The key point impeding the electrolysis process is the sluggish oxygen evolution reaction (OER) kinetics of the multi-electron charge transfer reaction resulting in high reaction overpotentials [3,4]. Researchers have shown an increased interest in 3d transition-metals OER electrocatalysts, especially in oxides with perovskite [5e7] and spinel structures [8e14], layered double hydroxides (LDH) [15e17] and carbides [18e20]. She et al reported an Sr(Co0.8Fe0.2)0.7B0.3O3Àd (SCFB0.3) perovskite realising ultrafast oxygen evolution with overpotential (h) at 10 mA cmÀ2 of 240 mV in 1.0 M KOH aqueous electrolyte [21]. The hybrid nanostructure of manganese cobaltite/nitrogen-doped multi-walled carbon nanotubes (MnxCo3-xO4@NCNTs) was proposed by Zhao et al and exhibited an overpotential of 470 mV at 10 mA cmÀ2 in 0.1 M KOH [25]
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