The design of efficient electrocatalysts for the oxygen evolution reaction (OER) is important for the conversion of renewable energy into storable fuels. However, the electrocatalytic OER is kinetically sluggish and often lacks stability in alkaline conditions. Transition metal carbides (TMCs) have recently emerged as low-cost OER electrocatalysts with high electrocatalytic activity and enhanced stability, competitive against high-cost state-of-the-art OER electrocatalysts such as metal oxides, RuO<sub>2</sub> and IrO<sub>2</sub>. Bimetallic TM-based catalyst systems can be used to enhance both stability and activity, for example the synergistic effects of Fe combined with Co or Ni can enhance electrocatalytic activity dependent on the amount of Fe incorporated into the system. To understand these synergistic effects, there has been tremendous efforts to study structure-activity-stability relationships for development of new OER electrocatalysts. Here, we demonstrate iron-cobalt and iron-nickel (Fe(Co/Ni))-Prussian blue analogue (PBA) metal organic frameworks (MOFs) employed as a single precursor for the synthesis of FeCo and FeNi nanocarbides, respectively. In both bimetallic TMC systems, we observed structural crystalline phase-dependent effects on the OER electrocatalytic activity. In particular, the nanocarbides with mixed crystal phases have enhanced OER activity compared to the pure phase bimetallic electrocatalysts. Mixed phase nanocarbide electrocatalysts with enhanced OER activity currently do not have well-understood morphological characteristics, which are crucial since morphology is known to impact electrochemical stability during OER.  Nanomaterials with amorphous structures that contain surface defects, rather than crystalline morphology, are known to reveal enhanced electrocatalytic activity and less ideal electrochemical stability which we hypothesize could similarly impact the performance of bimetallic nanocarbide electrocatalysts. To critically design low-cost bimetallic TMC systems, we identify structural descriptors for enhancing both electrocatalytic activity and electrochemical stability (quantified with voltammetric electrochemical methods) using phase composition characterization methods including x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS).

Phase and disorder-dependent effects on electrocatalytic activity of bimetallic Fe(Co/Ni) nanocarbides

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ACS Fall 2022

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