Molecular Engineering of Photocathodes based on Polythiophene Organic Semiconductors for Photoelectrochemical Hydrogen Generation.

Organic semiconductors provide significant potentials for the construction of photoelectrochemical (PEC) cells for solar hydrogen production because of their highly tunable properties. Herein, on carbon fiber paper (CFP) surface, pyridyl (Py), and 4,4'-bipyridin-1-ium (Py2+) groups were introduced into polythiophene (pTH) semiconductor by electrochemical copolymerization, respectively. After assembly with the Co(dmgBF2)2 type catalyst (CoB, dmgBF2 = difluoroboryldimethylglyoximate), the CoB@Py2+-pTH/CFP photocathode displayed nearly twice the photocurrent enhancement (550 μA cm-2 at 0.15 V vs reversible hydrogen electrode, RHE) comparing to that generated by the CoB@Py-pTH/CFP photocathode (290 μA cm-2 at 0.15 V vs RHE) for light-driven H2 generation under AM 1.5 solar illumination. Investigation of the mechanism revealed that the introduction of the positively charged pyridinium groups could improve the intrinsic Co(dmgBF2)2 catalyst activity for the H2 generation reaction. Meanwhile, the positively charged pyridinium groups serve as p-type dopants to increase the semiconductor bulk charge transfer rate and act as electron transfer mediators to promote the interfacial charge transfer kinetics between the catalyst and the pTH-based organic semiconductor.