Electrochemically in situ controllable assembly of hierarchically-ordered and integrated inorganic-carbon hybrids for efficient hydrogen evolution
Inorganic-carbon hybrid materials are an emerging class of nanostructured catalysts that can enhance various energy-oriented electrochemical reactions. Despite recent progress, it is still very challenging to controllably generate the hybrid carbon architecture and its inorganic components with a single approach. Inspired by the flexible redox properties of conductive polyaniline (PANI) polymer, we develop a redox-unit cooperative assembly strategy to synthesize hierarchically-ordered and integrated inorganic-carbon hybrids by electrochemically constructing the nanostructures of PANI and then modifying their redox states to controllably bond different metal complexes. The needle-branched PANI nanofibers are assembled in situ into a three-dimensional (3D) hierarchical framework on carbon paper by an anion induced electrochemical polymerization. Interestingly, tuning the redox states of PANI with a potentiostatic method achieves a controllable metal complex loading. The theoretical calculations show that the oxidized units can strongly bond metal complexes while reduced units don't react significantly due to a high formation energy. Both units with proper proportions can cooperatively control the concentration and spatial distribution of metal complexes in the PANI framework. After thermal treatment, the metal/PANI composites are transformed into a series of inorganic-carbon hybrids including metals and metal oxides, carbides, and sulfides. This novel strategy not only significantly improves the catalytic performance of non-noble metal hybrid materials but also greatly increases the utilization efficiency of noble metal catalysts in the hydrogen evolution reaction. Surprisingly, the optimized Pt@NC catalyst exhibits an ultrahigh mass activity that is ∼5.3-times better than the commercial Pt/C catalyst.