Cyanide-coordinated Fe(III) meso-tetra(4-carboxyphenyl) porphyrin as a possible electrocatalytic material for selective H ₂S oxidation

Electrodeposited Fe(III) meso-Tetra(4-carboxyphenyl) porphyrin with cyanide ligands coordinated to the central iron ion was investigated as a possible material capable of selectively oxidizing H ₂S in the presence of CO and NO in physiologically relevant solutions. Preliminary results suggest this to be an attractive material as it oxidized H ₂S at low potentials (0.15 V vs. AgAgCl) while exhibiting only mild activity toward both CO and NO. While this is a step in the right direction, the selectivity is currently inadequate for practical applications. Additionally, the electrocatalyst also exhibited a limited response at elevated sulfide concentrations, presumably due to the deposition of S ⁰ on the electrode surface. However, a cathodic-post run treatment was able to regenerate the electrochemical activity of the porphyrin-modified electrode surface by stripping any S ⁰ that deposited on the electrode surface during the H ₂S oxidation. The imperfect porphyrin coverage of the electrode surface and incomplete coordination of cyanide are suspected as the primary reasons for these shortcomings. Research is ongoing to remedy these limitations.