Highly Efficient Molecular Cobalt Electrode for (Photo)electrochemical Hydrogen Evolution

Abstract

Among the challenges in molecular electrocatalysis is how to increase the catalyst loading on electrode surface so as to enhance the catalytic efficiency. We found that, through electrochemical polymerization of the 1,10-phenanthroline ligand (phen), the [Co(tpy)(phen)Cl]Cl catalyst (mCo) can be fabricated on the electrode surface with a very high loading. Differential electrochemical mass spectroscopy (DEMS) measurements showed that, on such a poly[Co(tpy)(phen)Cl]Cl electrode (pCo), the onset potential of the hydrogen evolution reaction (HER) is only 370 mV in a buffer solution of pH = 3, with the TOF being 10 s–1 and a TON of ca. 2.2 × 106 at overpotential less than 0.5 V, which is among the best molecular catalysts thus found for HER. Characterized by X-ray photoelectron spectroscopy (XPS), the active site in pCo was found to be in molecular state, rather than in metallic state. By polymerizing mCo onto a Cu2O photocathode, a molecular catalyst/p-type semiconductor photocathode was realized for the HER, which can work stably at 0 V (vs RHE) under illumination, with the HER photocurrent increased by 40%, in comparison to that on bare Cu2O photocathode.