Carbon Nanofibers Featuring Bimetallic Nanoparticle-in-Pore Structures as Water-Splitting Electrocatalysts

Research effort has increasingly been devoted to exploiting efficient noble-metal-free electrocatalysts because of their low cost and abundancy. Herein, metallic nanoparticulate-containing carbon nanofibers (MCNFs) featuring interior, nanoparticulate-in-pore structures were fabricated by taking advantage of cationic metal species/anionic surfactant complexes (MSCs). Binary MSC mixtures containing Fe–Co, Fe–Ni, and Co–Ni species were used to control not only the size/loading amount of the metallic phases but also the microstructural characteristics of the nanofiber matrices. Compared to their single MSC counterparts, the binary MSC mixtures allowed the generation of unique metallic phases, such as binary transition-metal oxides, and resulted in enhanced surface area/porosity and reduced charge transfer resistance. The noble-metal-free MCNFs were demonstrated as electrocatalysts for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The MCNFs prepared using binary combinations of Fe–Ni and Co–Ni, viz., FeNiCNFs and CoNiCNFs, showed outstanding performances for the OER and HER, respectively. For the OER particularly, at potentials exceeding 1.6 V (vs RHE), the FeNiCNFs showed higher current densities than that of the well-known, conventionally used electrocatalyst RuO2. For overall water splitting, an asymmetric FeNiCNF∥CoNiCNF cell rendered performance stability that was 15% better than that of the RuO2∥Pt/C control cell. Based on the results of this study, various combinations of MSCs with controlled loading into functional matrices can be prepared to yield efficient, cost-effective electrocatalysts for water splitting.