Metallocomplex-based borohydride electro-oxidation catalysts

We have found that certain kind of complexes on carbon black catalyze borohydride electro-oxidation. All of the Rh porphyrins tested in this study exhibited high activity regardless of the structure of the porphyrin ligands. While other metalloporphyrins also catalyzed borohydride electro-oxidation, the activities were much lower than those of Rh porphyrins. Even Rh tetrakis(4-methylphenyl)porphyrin, which exhibited the highest activity, scarcely catalyzed the chemical decomposition of borohydride under open-circuit conditions. These metalloporphyrin-based catalysts tested do not promote H2 electro-oxidation. Other Rh complexes (Rh2Cl2(CO)4 and Rh phthalocyanin) also catalyze borohydride electro-oxidation. Rh2Cl2(CO)4 oxidizes borohydride at lower potentials than Rh porphyrins; it can catalyze borohydride even below 0 V vs. RHE. A one-compartment H2-generator that also generates electric power was constructed using Rh2Cl2(CO)4 as an anode catalyst.