A nanocoral like carbon composite based on dual-MOFs for catalytic reduction and evolution of oxygen

A nanocoral like composite was prepared by simply grinding the Fe-based metal-organic framework (NH 2 -MIL-53), Co-based metal-organic framework (ZIF-67) and dicyandiamide (DCDA) and subsequent pyrolysis treatment. The prepared composites displayed the hierarchical porous structure, the large specific surface area , and abundant N catalytic active sites. The optimal composite exhibited an excellent oxygen reduction reaction (ORR) activity with a half-wave potential (E 1/2 ) of 0.87 V (vs. reversible hydrogen electrode, RHE) which was higher than that of the commercial 20 wt% Pt/C. At the same time, the oxygen evolution reaction (OER) overpotential of the composite at 10 mA cm −2 (E j10 ) was 1.563 V, which was also lower than that of the commercial RuO 2 under the same conditions. The doping of DCDA increased the content of N, significantly improving the ORR and OER activities of the composites. The prepared composite exhibited excellent ORR/OER bifunctional catalytic activity with the ORR/OER potential gap (the potential difference, i.e., ΔE = E j10 - E 1/2 ) of only 0.693 V, lower than that of Pt/C + RuO 2 (ΔE = 0.763 V) under the same conditions. Assembled in the Zn-air battery, the prepared composite showed a better performance than Pt/C + RuO 2 (m: m = 1: 1). It provided a promising strategy for preparing the efficient bifunctional catalyst .