Synergistic amplification of (photo)catalytic oxygen and hydrogen generation from water by thin-film polypyrrole composites

Thin films of polypyrrole (PPy) containing nano-Ni ('nano-Ni') (as catalyst) and reduced graphene oxide (rGO) (as conductor) have been studied as (photo)electrocatalysts of the oxygen (O-2)-evolution reaction (OER) (at 0.8 V vs Ag/AgCl, in 0.2M Na2SO4, pH 12) and the hydrogen (H-2)-evolution reaction (HER) (at -0.75 V vs Ag/AgCl, in 0.05M H2SO4/0.2M Na2SO4) under light illumination of 0.25 sun. The above conditions were the most favorable for O-2/H-2-evolution under which the PPy and/or the nano-Ni constituents were not degraded. The industry benchmark catalyst, bare Pt, generated 0.15 mA/cm(2) for O-2-evolution and 2.2 mA/cm(2) for H-2-evolution under the above conditions. However, when the Pt was coated with PPy containing nano-Ni, and rGO in optimum molar ratios, it generated catalytic current densities that were 670 % larger for O-2-generation (0.97-1.0 mA/cm(2), including a photocurrent of 0.48 mA/cm(2)) and 18 % larger for H-2-generation (2.38-2.60 mA/cm(2), including a photocurrent of 0.20-0.40 mA/cm(2)), over periods of up to 50 h. EIS and Tafel plots indicated that these remarkable synergic amplifications derived from the combination of a high density of catalytic sites with the least-resistive conduction pathways, on average, within the coating. As catalytic accelerations of this type have previously only been observed with poly(3,4-ethylenedioxythiophene) (PEDOT), these results indicate that the principles of synergistic amplification also apply to other conducting polymer supports.