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

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.