The oxygen-buffering CeO2 effectively protects the available active sites of the ZIF-67-derived Co3O4@carbon to improve oxygen reduction/evolution reaction activities.

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Waste cornstalks and pomelo skins are used as carbon resources for preparing nanocomposites of iron oxide and partly graphitized carbon (Fe3O4/PGC-CS and Fe3O4/PGC-PS). The results showed that Fe3O4 with a face-centered cubic structure is uniformly dispersed on the skeleton of Fe3O4/GC, and the highest SBET values of Fe3O4/PGC-CS (476.5 m(2) g(-1)) and Fe3O4/PGC-PS (547.7 m(2) g(-1)) are obtained at 1000 °C. The electrical conductivity and density of catalytic active sites are correspondingly improved by the introduction of Fe species. Microbial fuel cells (MFCs) with a mixed composite (Fe3O4/PGC-CS:Fe3O4/PGC-PS = 1:1) cathode (three-dimensional structures) generate the highest power density of 1502 ± 30 mW m(-2), which is 26.01% higher than that of Pt/C (1192 ± 33 mW m(-2)) and only declines by 7.12% after 18 cycles. The Fe3O4/PGC-CS cathode has the highest Coulombic efficiency (24.3 ± 0.7%). The Fe3O4/PGC composites exhibit high oxygen reduction reactivity, low charge transfer resistances, and long-term stability and can be used as a low-cost and high-efficiency catalyst for MFCs.

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The design of rare-earth-metal oxide/oxysulfide catalysts with high activity and durability for the oxygen reduction reaction (ORR) is still a grand challenge at present. In this study, Ce-species (CeOS/CeO)/N, S dual-doped carbon (Ce-species/NSC) catalysts with promising oxygen storage/release capacities are prepared at different temperatures (800-1000 °C) to enhance the ORR efficiency. Mechanisms for the effects of temperature on crystalline phase transition between CeO and CeOS and structure evolution of Ce-species/NSCs are inferred to better understand their catalytic activity. Porous CeOS/NSC (950 °C) catalyst as the air-breathing cathode exhibits a maximum power density of 1087.2 mW m, which is higher than those of other Ce-species/NSCs and commercial Pt/C (989.13 mW m) in microbial fuel cells. The decline of the power density of CeOS/NSC (950 °C) cathode is 8.7% after 80 days of operation, which is far lower than that of Pt/C (36.7%). CeOS/NSC (950 °C) has a four-electron selectivity toward the ORR and a low charge-transfer resistance (5.49 Ω), contributing to high ORR activity and durability. The promising ORR catalytic activity of CeOS/NSC (950 °C) is attributed to its high specific surface area (338.9 m g), varied active sites, high electrical conductivity, and sufficient oxygen vacancies in the CeOS skeleton. The high content of Ce in CeOS/NSC (950 °C) facilitates the formation of more oxygen-deficient Ce sites that generate more oxygen vacancies to release/store more oxygen to stabilize the available oxygen for the ORR. Thus, this study provides a new perspective for preparation and application of this new type of the ORR catalyst.

To improve the sluggish kinetics of the methanol oxidation reaction (MOR), one efficient way is to improve the properties of catalyst supports to enhance the activity and durability of Pt-based catalysts.