Synergistic Amplification of Water Oxidation Catalysis on Pt by a Thin-Film Conducting Polymer Composite

Abstract

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.

Synergistic Amplification of Oxygen Generation in (Photo)Catalytic Water Splitting by a PEDOT/Nano‐Co3O4/MWCNT Thin Film Composite

“…In previous work ,[2][3] we investigated the factors that led to a maximization of the catalytic activity in such systems. We demonstrated that the key to achieving a large catalytic effect was to deploy the conducting polymer support as a thin film that simultaneously maximizes the number of catalytic sites in the film and the conductivity of the pathways by which they are electrically connected to the electrode . This approach yields the largest and most active electrocatalytic area and therefore the greatest effect .…”

“…However, achieving it requires a fine balance between the number/density of catalytic/conducting sites present and the overall conductivity/thickness of the film. Using this technique we have previously demonstrated catalytic performances that exceeded that of a Pt surface by up to ∼6‐fold . Pt is an industry standard water oxidation catalyst that provides a comparative reference when using unique test conditions that have that have not been employed in other studies of OER catalysts.…”

“…To assess how sustained the current density of the most active film was, we tested it for 35 h, with and without light‐illumination, in a previously‐described sealed cell that allowed for collection of the gases produced (Figure S5). Figure shows its performance on the Pt/FTO substrate over this period.…”

“…Conducting polymers like poly(3,4-ethylenedioxythiophene) (PEDOT) have been widely used to immobilize water oxidation catalysts on light-active semiconductor electrodes in photoelectrochemical (PEC) cells. [1] In previous work , [2] [3] we investigated the factors that led to a maximization of the catalytic activity in such systems. We demonstrated that the key to achieving a large catalytic effect was to deploy the conducting polymer support as a thin film that simultaneously maximizes the number of catalytic sites in the film and the conductivity of the pathways by which they are electrically connected to the electrode.…”

“…[2] This approach yields the largest and most active electrocatalytic area and therefore the greatest effect. [2] However, achieving it requires a fine balance between the number/ density of catalytic/conducting sites present and the overall conductivity/thickness of the film. Using this technique we have previously demonstrated catalytic performances that exceeded that of a Pt surface by up to~6-fold.…”