Influence of Composition on Performance in Metallic Iron–Nickel–Cobalt Ternary Anodes for Alkaline Water Electrolysis

Abstract

Metallic electrodes based on iron, nickel, and/or cobalt have re-emerged as promising cost-effective anodes for the alkaline oxygen evolution reaction (OER) due to their simplicity and their in situ formation of a highly active oxy-hydroxide surface catalyst layer, which exhibits state-of-the-art overpotentials for the OER. However, the effect of alloy composition has not been systematically studied. Herein, using metallic anodes with defined Fe–Ni–Co atomic ratios prepared via arc melting, we report the relationship between the initial alloy composition, the OER performance, and the emergent active catalyst composition. After 50 h operation at 0.5 A cm–2 the most active initial alloys (having a moderate amount of cobalt <40 at. %, an iron proportion between 30 and 80 at. % and a nickel ratio below 60 at. %) gave average overpotentials for 10 mA cm–2 ca. 300–320 mV and Tafel slopes of 35–50 mV dec–1. Iron and nickel-rich alloys performed poorer. The oxyhydroxide OER catalyst formed on the anode surface generally showed an increased concentration of Co and Ni and a depletion of Fe compared to the initial metal composition, giving the most active OER catalyst at a composition of Ni and Co of ca. 40 at. % with Fe at ca. 20 at. %. However, the initial alloy composition of Fe12.5Co12.5Ni75, showed a nearly invariant surface metal composition, indicating this as the most stable composition. Further analysis of the surface identified no correlation of the mass of metals leached from the anode surface, the electrochemically active surface area, or the presence of active Ni2+/3+ redox surface sites to the OER performance suggesting these factors do not influence the results.

Anodic Transformation of a Core‐Shell Prussian Blue Analogue to a Bifunctional Electrocatalyst for Water Splitting

“…To the best of our knowledge, the mass activity for our NiCo@A-NiCo-PBA-AA is the highest among the reported PBA-based catalysts. [41][42][43] The enhanced catalytic activity of NiCo@A-NiCo-PBA-AA catalyst results from the amorphous shell and electrochemical activation.…”

Constructing a Hetero-interface Composed of Oxygen Vacancy-Enriched Co3O4 and Crystalline–Amorphous NiFe-LDH for Oxygen Evolution Reaction

“…In general, the design of high-performance OER electrocatalysts is mainly based on the following aspects: optimizing the collocation of components, regulating the morphology, and adjusting the microstructure. − For thermodynamic factors, the collocation of components and microstructure play the key roles in affecting the catalytic activity. Typically, noble-metal-based materials (e.g., RuO 2 and IrO 2 ) possess excellent activity toward the OER but are unsuitable for further practical applications owing to their high price and scarcity. , Transition metals have recently attracted remarkable attention from researchers for their unique electronic structure characteristics and excellent catalytic performance. − Among them, iron, cobalt, and nickel as “celebrity” elements exhibit outstanding OER performance and are used for designing OER electrocatalysts. − Simultaneously, according to the mechanism of OER, micro-structured electrocatalysts with abundant active sites are considered extraordinary potentials for OER. , On the basis of previous theoretical calculations and experimental verification, Co 3 O 4 with a one-dimensional (1D) nanowire structure exhibits exceptional catalytic activity for OER but is quite mediocre in terms of driving kinetics .…”

A Self‐Reconstructed Bifunctional Electrocatalyst of Pseudo‐Amorphous Nickel Carbide @ Iron Oxide Network for Seawater Splitting

“…The relatively lower Tafel slopes of NiFe‐PBA‐gel‐cal indicate the generation of NiC x results in higher reaction activity and transfer coefficient. [ 41 , 42 ] Figure 3d shows the stability of NiFe‐PBA‐gel‐cal in freshwater and simulated seawater, as determined in a chronoamperometry test. Only a negligible decrease in current density was observed after 60 h measurement, maintaining ≈98.4% in freshwater and ≈96.2% in simulated seawater, showing the excellent durability of NiFe‐PBA‐gel‐cal.…”