Despite their potential for facilitating high activity, thin-film conducting polymer supports have, historically, expedited only relatively weak performances in catalytic water oxidation (with current densities in the μA/ cm2 range). In this work, we have investigated the conditions under which thin-film conducting polymers may synergistically amplify catalysis. A composite conducting polymer film has been developed that, when overcoated on a bare Pt electrode, amplifies its catalytic performance by an order of magnitude (into the mA/cm2 range). When poised at 0.80 V (vs Ag/AgCl) at pH 12, a control, bare Pt electrode yielded a current density of 0.15 mA/cm2 for catalytic water oxidation. When then overcoated with a composite poly(3,4-ethylenedioxythiophene) (PEDOT) film containing nanoparticulate Ni (nano-Ni) catalyst and reduced graphene oxide (rGO) conductor in the specific molar ratio of 4.5 (C; PEDOT): 1 (Ni): 9.5 (C; other), the electrode generated water oxidation current densities of 1.10-1.15 mA/cm2 under the same conditions (over >50 h of operation; including a photocurrent of 0.55 mA/cm2 under light illumination of 0.25 sun). Control films containing other combinations of the above components, yielded notably lower currents. These conditions represent the most favorable for water oxidation at which PEDOT does not degrade. Studies suggested that the above composite contained an optimum ratio of catalyst density to conductivity and thickness in which the PEDOT electrically connected the largest number of catalytic sites (thereby maximizing the catalytically active area) by the shortest, least-resistive pathway (thereby minimizing the Tafel slope). That is, the amplification appeared to be created by a synergistic matching of the connectivity, conductivity, and catalytic capacity of the film. This approach provides a potential means for more effectively deploying thin-film conducting polymers as catalyst supports.

Amplifying catalysis by thoughtful exploitation of synergistic effects with interacting supports is a new field of potentially great significance. It is particularly relevant for solar‐assisted reactions that are currently too poorly catalyzed to be practically viable, such as photoelectrochemical splitting of water to produce hydrogen and oxygen. In this work we describe synergistic amplification of water oxidation photoelectrocatalysis by the use of a thin layer electroactive polymer support. Coating of a bare Pt surface with a 0.98 μm thick film of poly(3,4‐ethylene‐dioxythiophene) (PEDOT) containing a specific molar ratio of nano‐Co3O4 (a water oxidation catalyst) and multi‐wall carbon nanotubes (oxidatively stable conductors) synergistically amplifies its rate of water oxidation catalysis by 15‐fold (under the most oxidizing conditions that can be applied to PEDOT without degradation; with light illumination of 0.25 sun). To the best of our knowledge, this film is the most active water oxidation catalyst yet reported under near‐neutral (pH 12) conditions as a proportion of the activity of Pt, which is the industry‐standard catalyst of the reaction.