EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Mesoporous Co-based transition metal oxides and their electrocatalytic performance have been very well studied [1,2]. Combining two and more metals in the oxide structure is known to improve their intrinsic properties and performances. Here, we developed a series of ordered mesoporous Cu/Ni/Co oxides (CNCO) with variable composition to assess the role of hetero-metals and their synergy on their electrocatalytic performances towards OER. The porosity, mesostructure, and phase and elemental compositions were characterized in detail. Most Cu and Ni were incorporated into the spinel structure of Co3O4 resulting in (Cu,Ni)xCo3-xO4 with only a small amount of impurities, such as CuO and NiO. Regarding electrocatalytic activity and stability of these high surface area materials, it was found that Ni-rich CNCO outperforms bimetallic Ni/Co and Cu/Co oxides in 1M KOH electrolyte, being activated over 200 CVs. As a result, the most active material CNCO-2-8 (Cu/Ni~1/4) exhibits a current density of 411 mA cm-2 and an overpotential of 312 mV after the activation process. Following this, to exclude any activation due to the interaction of Ni with Fe impurities present in the electrolyte, and to investigate the intrinsic role of Cu, the activity of the electrocatalysts was also investigated in purified 1M KOH. High loading of Cu in CNCO enhanced the activity of the Cu/Ni/Co oxides. However, the most active and stable catalyst was found to be CNCO-5-5 (Cu/Ni~1/1) and not the Cu-rich CNCO-8-2, presumably due to higher dissolution of CuO species in the alkaline media. Summarizing, Cu/Ni (Cu/Ni≤1/1) inclusions in Co oxide provide a high number of active sites resulting in a highly efficient and stable catalyst for OER in both purified and non-purified alkaline solutions.
[1] H. Tüysüz et al., Nano Res. 2013, 6, 47.
[2] J. Wang et al., Adv. Mater. 2016, 28, 215.