Developing efficient catalysts for the OER and ORR using a combination of Co, Ni, and Pt oxides along with graphene nanoribbons and NiCo2O4

Abstract

Hydrogen storage in large quantities needs 10 to 40 years to be commercially ready to be employed for electricity generation. Hydrogen used in fuel cells can be derived from electrolyzers via a green energy mechanism. Platinum group metals (PGMs) are widely used in the fabrication of fuel cells and electrolyzers, which are in turn employed in electrocatalysing reactions such as the hydrogen and oxygen evolution reactions (HER and OER) and oxygen reduction reaction (ORR). This work sought to develop efficient electrocatalysts for the OER and ORR based on the combination of Ni and Co oxides with or without NiCo₂O₄, blended with or without graphene nanoribbons (GNRs) and containing a low content of Pt. Among the electrocatalysts investigated, crystalline NiCo₂O₄ was found to be the best and most stable electrocatalyst for the OER; the enhancement of the electrocatalytic properties of this catalyst was associated with the synergistic effects of binary metal ions, such as Co²⁺, Co³⁺, Ni²⁺, and Ni³⁺ (transition metals intercalated across the nanostructures). Similarly, PtCoNi/GNR was found to be the best and most stable electrocatalyst for the ORR; the improvement observed in the ORR properties of this catalyst was attributed to three factors: (i) the presence of Pt⁰ and Pt²⁺ metal/ions in the CoNi/GNR nanocomposites; (ii) the synergistic effects of Pt metal/ions with binary metal ions such as Co²⁺, Co³⁺, Ni²⁺, and Ni³⁺ (transition metals intercalated across the nanostructures); and (iii) the metal/ions–support interactions (geometric effects and charge transfer—that produce electron-deficient Pt^δ+ species, resulting from strong interaction between Pt and Co and Ni hydroxides/oxides at the PtCoNi/GNR nanocomposite interface). The PtCoNi/GNR′/GC electrode was developed using a low content of Pt (22.5 μg_Pt cm⁻²).