Electrocatalytic materials design for oxygen evolution reaction

Highly robust, novel aluminum counter cation-based monophosphate tungsten bronze electro-catalysts for oxygen evolution in acidic solution

This study describes the successful synthesis of novel bronze with a low tungsten oxidation state for the efficient electro-catalytic oxidation of water. An extraordinarily robust monophosphate tungsten bronze (MPTB)-modified graphite anode was successfully fabricated for the oxygen evolution reaction (OER) at a thermodynamic potential of 1.23 V in H2SO4 acidic solution. Several Al, Cr and Fe counter-cation-based MPTBs were synthesized by the solution combustion method. Novel Al-based MPTBs calcined at 700 °C in O2 (AlO7) showed almost zero onset overpotential, high current density, high turnover frequency for OER and steady catalysis in repeated use even after 30 weeks. The orthorhombic AlO7 comprising crystallites of 9.89 nm and an indirect band gap (1.89 eV), is an unusually stable MPTB that contains 98% W5+ state stabilized with the Al3+ counter cation. The catalysis decreases as the ratio of W5+ : W6+ in MPTBs decreases and [410] and [601] facets play main roles in the first H2O association and nucleophilic attack of the second H2O molecule on the catalyst surface. Thus, MPTBs can be non-noble metal anode materials for robust acidic H2O electrolyzers.

In need of a second-hand? The second coordination sphere of ruthenium complexes enables water oxidation with improved catalytic activity

A ligand dangling arm, acting as an intramolecular proton acceptor, drastically increasing the catalytic activity of Ru-complexes for water oxidation.

Cobalt Carbonate as an Electrocatalyst for Water Oxidation

Co^II salts in the presence of HCO₃ ^- /CO₃ ^2- in aqueous solutions act as electrocatalysts for water oxidation. It comprises of several key steps: (i) A relatively small wave at E_pa ≈0.71 V (vs. Ag/AgCl) owing to the Co^III/II redox couple. (ii) A second wave is observed at E_pa ≈1.10 V with a considerably larger current. In which the Co^III undergoes oxidation to form a Co^IV species. The large current is attributed to catalytic oxidation of HCO₃ ^- /CO₃ ^2- to HCO₄ ^- . (iii) A process with very large currents at >1.2 V owing to the formation of Co^V (CO₃ )₃ ^- , which oxidizes both water and HCO₃ ^- /CO₃ ^2- . These processes depend on [Co^II ], [NaHCO₃ ], and pH. Chronoamperometry at 1.3 V gives a green deposit. It acts as a heterogeneous catalyst for water oxidation. DFT calculations point out that Coⁿ (CO₃ )₃ ^n-6 , n=4, 5 are attainable at potentials similar to those experimentally observed.