The development of highly active and stable earth-abundant catalysts to reduce or eliminate the reliance on noble-metal based ones in green and sustainable (electro)chemical processes is nowadays of great interest. Here, N-, O-, and S-tridoped carbon-encapsulated Co 9 S 8 (Co 9 S 8 @NOSC) nanomaterials are synthesized via simple pyrolysis of S-and Co(II)-containing polypyrrole solid precursors, and the materials are proven to serve as noble metal-free bifunctional electrocatalysts for water splitting in alkaline medium. The nanomaterials exhibit remarkable catalytic performances for oxygen evolution reaction in basic electrolyte, with small overpotentials, high anodic current densities, low Tafel slopes as well as very high (nearly 100%) Faradic efficiencies. Moreover, the materials are found to efficiently electrocatalyze hydrogen evolution reaction in acidic as well as basic solutions, showing high activity in both cases and maintaining good stability in alkaline medium. A two-electrode electrolyzer assembled using the material synthesized at 900 °C (Co 9 S 8 @NOSC-900) as an electrocatalyst at both electrodes gives current densities of 10 and 20 mA cm −2 at potentials of 1.60 and 1.74 V, respectively. The excellent electrocatalytic activity exhibited by the materials is proposed to be mainly due to the synergistic effects between the Co 9 S 8 nanoparticles cores and the heteroatom-doped carbon shells in the materials.

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To achieve optimal performance of fuel cells and metal‐air batteries, searching the cost‐effective catalysts with enhanced activity and durability for oxygen reduction reaction (ORR) is highly pursued. We present a new and scalable approach to synthesize low‐cost Co and N co‐doped C (CoNC) catalysts from sustainable organic‐rich chitosan waste. The CoNC designed here involves in chelation between the chitosan and Co ions, shows superior ORR activity. The XPS spectra demonstrate the kinds of ORR active N sites are of high content in the CoNC, which lead to preferable catalytic activity. The TEM images show more highly dispersion of Co, N and C in the CoNC, which contributes to the high ORR activity. The CoNC catalysts exhibit a remarkable limiting current of ∼5.36 mA cm−2 and positive onset potential of −0.105 V (vs. Ag/AgCl), both of which are comparable to those of the commercial Pt/C. Additionally, the optimal CoNC also possesses prominent durability and tolerance of methanol.

Fe3O4 nanoparticles composed of 14-facet and 26-facet polyhedrons exhibited a high initial discharge capacity of 1067 mA h g−1.