Photoelectrochemical Hydrogen Production by a Porphyrinic Metal–Organic Framework Thin Film on p-Type Silicon

Abstract

The ongoing demand to power our society dictates the need for fossil-free fuels. Herein, the metal–organic framework (MOF) catalyst Al₂(OH)₂CoTCPP was grown as a thin film on a p-type silicon semiconductor (SC) for photoelectrochemical (PEC) fuel production. The MOF@Si composite catalyzes hydrogen production under illumination at an applied potential that is 320 mV more positive than that of the same MOF on a dark conducting substrate. An interesting feature of the study relates to the product speciation, as metalloporphyrins are known to catalyze both H₂ evolution as well as CO₂ reduction. In aqueous bicarbonate electrolyte and in the presence of CO₂, hydrogen is detected as the sole product after chronoamperometry (CA). In fact, the MOF@Si composite catalyzed H₂ evolution with a faradaic efficiency of close to 100%. The role of the MOF as a catalyst could be established by comparing the current response of the MOF@Si photoelectrode with that of bare silicon, with the former showing more than 30-fold higher currents. Comprehensive characterization of the Al₂(OH)₂CoTCPP@Si composites by scanning electron microscopy and X-ray photoelectron spectroscopy before and after PEC experiments confirms the stability of the MOF under the experimental conditions.