Low-price, high-performance and strong-stability electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are highly significant in the application of clean energy devices like rechargeable zinc-air batteries and renewable fuel cells. In this paper, a Prussian blue analogue Co3­[Fe­(CN)6]2·nH2O (Co-Fe PBA), as a well-known member of the metal–organic framework family, was electrospun into polyacrylonitrile (PAN) nanofibers to obtain composite Co-Fe PBA@­PAN nanofibers. Nitrogen-doped carbon nanofibers encapsulated FeCo alloy nanoparticles (FeCo-NCNFs-Ts, T = 700, 800, 900 °C) were synthesized by pyrolysizing Co-Fe PBA@­PAN precursor at different temperatures under an argon atmosphere. The effects of different calcination temperatures and mass ratios between Co-Fe PBA and PAN on ORR/OER catalytic activity were explored. Among FeCo-NCNFs-Ts, FeCo-NCNFs-800 had the highest bifunctional electrocatalytic performance with a lower reversible overvoltage of 0.869 V between ORR (E 1/2) and OER (E j = 10 mA cm–2), excellent stability and methanol durability, which even exceeded those of Pt/C and RuO2. The superb bifunctional activity for FeCo-NCNFs-800 was comparable to that of non-noble electrocatalysts reported in recent literatures. Moreover, the zinc-air battery based on the FeCo-NCNFs-800 air-cathode catalyst had a high power density of 74 mW cm–2 and strong cycling stability (125 cycles for 42 h), which can be comparable to a Pt/C-RuO2 zinc-air battery. The impressive bifunctional activity on ORR and OER for the FeCo-NCNFs-800 catalyst in the zinc-air battery can be attributed to the synergistic effects of the one-dimensional fibrous structure, FeCo alloy nanoparticles, Co-N (pyridinic-N) active sites, and numerous mesopores.

Electrocatalytic water-splitting catalysts play important roles in clean energy conversion systems. Herein, metal–organic framework-derived (MOF-derived) hollow CoS x @MoS2 microcubes were successfully synthesized by a novel method. Co-MOF [(CH3)2NH2]­[Co­(HCOO)3] prepared by a simple liquid precipitation method at room temperature reacted with S2– released from thioacetamide (TAA) to generate Co9S8 under solvothermal conditions. Through hydrothermal treatment, numerous MoS2 nanosheets grew on the surface of CoS x vertically and uniformly after introduction of sulfur and molybdenum sources, finally generating CoS x @MoS2 heterostructures. As bifunctional electrocatalysts, the heterostructures exhibited remarkable performance for the hydrogen evolution reaction with a low overpotential of 239 mV when the current density increased up to 10 mA cm–2 and a small Tafel slope of 103 mV dec–1 in 0.5 M H2SO4. They also worked effectively for the oxygen evolution reaction with a low overpotential of 347 mV at 10 mA cm–2 in 1 M KOH. The enhanced electrocatalytic activities of CoS x @MoS2 can be ascribed to their unique heterostructures and the synergism between CoS x and MoS2.

Cobalt-based, nitrogen-doped porous carbon materials with in situ grown carbon nanotubes (CNTs) were synthesized by the facile carbonization of porous 3D Bio-MOF-11 [Co2(ad)2(CH3COO)2]·2DMF·0.5H2O (ad = adenine). Co-N/PC@CNT-Ts inherit the octahedral shape from the precursor, and have a porous structure with in situ grown CNTs catalyzed by Co particles. Co-N/PC@CNT-T materials have excellent activities as bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in 0.1 M KOH electrolyte. Among the Co-N/PC@CNT-Ts, Co-N/PC@CNT-700 has the highest electrocatalytic activity. For ORR, Co-N/PC@CNT-700 has a higher onset potential of 0.92 V vs. reversible hydrogen electrode (RHE), high stability and methanol tolerance, which are even better than that of Pt/C. For OER, it has a low potential of 1.63 V at a current density of 10 mA cm-2. In addition, Co-N/PC@CNT-700 affords a low reversible overvoltage (bifunctional performance parameter) of 0.862 V between ORR and OER compared to the current advancing bifunctional catalysts. The superb bifunctional activity can be attributed to uniform CoNx active sites embedded in graphitized carbon, unique in situ grown CNT structure and ordered mesoporous structure. The synergistic effect enlarged the contact surface, exposed more active centers and provided many pathways, thereby boosting the electrocatalytic performance. In conclusion, this study provides a novel avenue for the application of stable transition metal-based, nitrogen-doped carbon materials as extremely efficient electrocatalysts for ORR and OER.

To solve energy-related environmental problems and the energy crisis, efficient electrochemical materials have been developed as alternative energy storage and conversion systems. Abundant transition metalsa nd their sulfides are attractive electrochemical materials. Herein, we report an efficient phosphorization strategy,w hich improves the overall electrochemical performance of metal sulfides. In detail, CoS hexagonal bipyramids were synthesized through simple calcination combined with in situ sulfurizationo fa cobalt-based metal-organic framework template, and then phosphate ion-functionalized CoS (P-CoS)w as prepared through ap hosphorization reaction.P-CoS exhibited outstandinge lectrochemical activity as both supercapacitor electrode and oxygene volution reaction (OER) catalyst. Supercapacitors based on CoS and P-CoS as the electrodes had high specific capacitances of 304 and 442 Fg À1 ,r espectively, and remaineds table for over 10 000 cycles at 5Ag À1 .F or OER, P-CoS showed ac urrent density of 10 mA cm À2 at an overpotentialo f3 40 mV,w ith as mall Ta fel slope. In conclusion, functionalizing CoS with phosphate ions is ap romising method fore nhancing chemical reactivity and accelerating ion and electront ransfer.