Visible-light driven photocatalytic oxygen evolution reaction from new poly(phenylene cyanovinylenes)

Two new n-type conjugated polymers, poly(N-(2-ethylhexyl)-3,6-carbazole-p-bis(2-ethylhexyloxy)-phenylene cyanovinylene) (P1) and poly(N-(2-ethylhexyl)-3,6-carbazole-p-bisdodecyloxy-phenylene cyanovinylene) (P2) were synthesized and explored for their photo-electrochemical catalytic activity for oxygen evolution reaction (OER). When these polymers were used as photoanodes under visible light irradiation, oxygen evolution occurred at over potential as low as +0.6 V vs. SCE. In the chronoamperometric (CA) measurements, the photo-current density generated at +0.6 V by P1 and P2 was 0.31 and 0.27 μA/cm2, respectively. This is an excellent performance of a metal free and without the use of sacrificial electron donors polymer photoanodes. The higher photoelectrochemical (PEC) performance of P1 was attributed to its narrow band gap and larger surface area. Moreover, the drastic quenching of the photoluminescence (PL) emission intensity of P1 suggested the recombination of charges was effectively suppressed, which is in excellent agreement with our experimental observations. In the linear sweep voltammetry (LSV) measurements, the onset potential was observed at around 0.73 V whereas the maximum current densities by P1 and P2 were realized at 0.39 mA/cm² and 0.15 mA/cm², respectively. Long-term stability testing via CA indicated that P1 was more stable than P2, which warranted its potential as photocatalyst for solar water splitting. In addition, the optical band gaps of P1 and P2, derived from the onset absorption edge, were found to be 2.51 and 2.62 eV, respectively, and the band gaps measured by Kubelka−Munk (KM), cyclic voltammetry (CV) and computational methods were found to be consistent. These polymers are readily soluble in common organic solvents which make them potential candidates for photovoltaic devices application.