Structural Features of Porous CoFe Nanocubes and Their Performance for Oxygen‐involving Energy Electrocatalysis

The structural properties of CoFe composites fabricated from inexpensive Co(II) and Fe(III) precursors using a Prussian blue analogue (PBA) strategy without additional reductants were investigated. Microporous CoFe‐200 and microporous/mesoporous CoFe‐550 structures of the CoFe catalysts (CoFe‐PBA) were produced by calcination for 1 h in N 2 at 200 °C or 550 °C, respectively. The electrocatalytic activities of the CoFe catalysts produced for the oxygen evolution and reduction reactions (OER/ORR) were studied in alkaline media. The OER measurements revealed the CoFe‐200 catalyst to be superior to CoFe‐PBA and CoFe‐550, and even surpass the activity of commercial Ir/C in terms of the overpotential at 10 mA cm −2 and onset potential ( E o n s e t O E R ). On the other hand, the ORR activity of CoFe‐550 exhibited a more positive half‐wave potential (0.837 V vs. RHE) and E o n s e t O R R(0.942 V vs. RHE) than CoFe‐200. The Tafel slope (−55.9 mV dec −1 ) of CoFe‐550 was lower than that of Pt/C (−77.8 mV dec −1 ). A comparison of CoFe‐200 and CoFe‐550 suggested that the microporosity of CoFe‐200 (average pore diameter, d ≤2 nm) was beneficial in terms of the OER. In contrast, the mesoporous ( d ≈35.6 nm) structure of CoFe‐550 promoted the mass‐transport kinetics of oxygen through the electrode surface. CoFe nanocubes with tunable porosity are potential catalysts that can be utilized selectively for the OER and ORR.