273566 Polyaniline-Modified Pt Catalyst for Improved Electrochemical Reduction of CO2

Monday, October 29, 2012: 2:10 PM
321 (Convention Center )
David N. Abram, Kendra P. Kuhl, Etosha R. Cave and Thomas F. Jaramillo, Chemical Engineering, Stanford University, Stanford, CA

Alternative energy sources are being extensively explored such as wind and solar energy.  Due to their intermittency, it will be difficult for grids to handle a large percentage  of their energy coming from these sources.  This energy could be stored in chemical bonds by converting CO2 and water to fuels and oxygen, creating a carbon neutral cycle.  Heterogeneous catalysts studied for the CO2 reduction reaction in aqueous environments consist mainly of metals, which produce varied product distributions but all require large overpotentials.1 Some attempts to improve catalysts include alloys and chemical modification of metal surfaces.2-4 This study uses surface chemical modification in an effort to tune the product distribution or lower the overpotential required for electrochemical CO2 reduction on metal catalysts. The metal catalyst explored was platinum, which is actually a poor aqueous CO2 reduction catalyst since it primarily just reduces the protons to H2. Polyaniline (PANi) was chosen as the chemical modifier to interact with the CO2 at the catalyst surface. CO2 electrolysis experiments were run for 1 hour potentiostatically using a custom electrolysis cell with a large working electrode area to electrolyte volume ratio for increased sensitivity of liquid products. Gas Chromatography (GC) and Nuclear Magnetic Resonance (NMR) were used to detect gas and liquid products, respectively. The PANi was electrodeposited on the Pt foil substrates using cyclic voltametery.  These PANi-Pt catalysts as well as the bare Pt foils were tested at a variety of potentials that spanned current densities from  0.5 to 15 mA/cm2. The Pt foils performed similar to literature reports, with H2 as the dominant product with formate (<0.4%) as a minor product.1 However, CO, methane, and methanol were also detected in small amounts (<0.2%), which were seen in one report.5 The PANi-Pt catalysts show a small but noticeable increase in efficiency for formate (up to 1.5%) and CO (up to 0.8%)  and a decrease in methanol production compared to the pure Pt metal catalyst.  The possibility that the efficiency increased due to degradation of the PANi film was ruled out using a C13-labeled CO2 experiment and H1 NMR analysis of the formate. The current hypothesis is that the amine groups in the leucoemeraldine form of the PANi interact with the CO2 intermediates at the surface of the Pt catalyst to lower the barrier for the rate-limiting step for the 2e- products, CO and HCOO-. Ongoing work is aimed at exploring this hypothesis to develop the mechanistic understanding needed to develop more efficient catalysts. 


The authors would like to thank the Global Climate and Energy Project, Chevron and the Stanford Graduate Fellowship (SGF), and the National Science Foundation (NSF) for funding.


  1. Hori et al. Electrochimica Acta, 39, 1833-1839, 1994.
  2. K. Ogura et al. J. Electrochem. Soc., 145, 3801-3809,1998.
  3. B. Aurian-Blajeni et al. J. Electroanal. Chem., 149, 291-293, 1983.
  4. R. Aydin et al. J. Electroanal. Chem., 535, 107-112, 2002.
  5. G.M. Brisard et al. Electrochem. Comm., 3, 603-607, 2001.

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