PEFC Electrode with Enhanced Three-Phase Contact and Built-In Supercapacitive Behavior

Abstract

Hydrous ruthenium oxide, which exhibits both protonic and electronic conduction, is incorporated in the cathode electrocatalyst layer of the membrane electrode assembly for polymer electrolyte fuel cells ͑PEFCs͒. The supercapacitive behavior of ruthenium oxide helps realize a fuel cell-supercapacitor hybrid. Platinum ͑Pt͒ nanoparticles are deposited onto carbon-supported hydrous ruthenium oxide and the resulting electrocatalyst is subjected to both physical and electrochemical characterization. Powder X-ray diffraction and transmission electron microscopy reflect the hydrous ruthenium oxide to be amorphous and well-dispersed onto the catalyst. X-ray photoelectron spectroscopy data confirm that the oxidation state of ruthenium in Pt anchored on carbon-supported hydrous ruthenium oxide is Ru 4+ . Electrochemical studies, namely cyclic voltammetry, cell polarization, intrinsic proton conductivity, and impedance measurements, suggest that the proton-conducting nature of hydrous ruthenium oxide helps extend the three-phase boundary in the catalyst layer, which facilitates improvement in performance of the PEFC. The aforesaid PEFC operating with hydrogen fuel and oxygen as oxidant shows a higher power density ͑0.62 W/cm 2 @ 0.6 V͒ in relation to the PEFC comprising carbon-supported Pt electrodes ͑0.4 W/cm 2 @ 0.6 V͒. Potential square-wave voltammetry study corroborates that the supercapacitive behavior of hydrous ruthenium oxide helps ameliorate the pulse-power output of the fuel cell. In the postoil energy economy, hydrogen-based fuel cells are being perceived as a possible energy alternative. Hydrogen-based polymer electrolyte fuel cells ͑PEFCs͒ are most promising as they offer an order of magnitude higher power density than any other fuel cell system. A PEFC is fed with hydrogen, which is oxidized at the anode and oxygen that is reduced at the cathode. The protons released during the oxidation of hydrogen pass through the proton exchange membrane to the cathode. The electrons released during the oxidation of hydrogen travel through the external electric circuit, generating an electric current. Owing to the high degree of irreversibility of the oxygen reduction, even under open-circuit condition, the overpotential of the oxygen electrode in a PEFC happens to be about 0.2 V. This represents a loss of about 20% from the theoretical maximum efficiency for a PEFC. Accordingly, the PEFC cathode electrocatalyst has to possess a high intrinsic activity for the electrochemical reduction of oxygen at the cathode in order to attain the maximum efficiency of the PEFC. 1,2The activity of the cathode catalyst is reportedly improved by design of the tailored catalyst with controlled composition and microstructure. Nevertheless, the high activity of the catalyst itself is necessary, but not a sufficient condition for good fuel cell performance. To ensure the optimum conditions for effective catalyst utilization, an environment must be provided that allows for an adequate supply of reactants as well as good connectivity of the acti...

Understanding the Bifunctional Effect for Removal of CO Poisoning: Blend of a Platinum Nanocatalyst and Hydrous Ruthenium Oxide as a Model System

“…Because XPS provides information about the surface, where the electrocatalytic reactions take place, XPS results may complement the XANES data that provide information about bulk properties. Pt 4f XPS spectra of Pt/C and Pt/C_RuO x H y are displayed in panels c and d of Figure , respectively, and the results were fitted into two sets of doublets (see Table for detailed fitting results). − The differences in peak positions and the ratio of Pt 0 and Pt 2+ states of the two samples were negligible, and this reveals that the surface chemical state of nanosized Pt is not affected by RuO x H y .…”

A Methanol-Tolerant Carbon-Supported Pt−Au Alloy Cathode Catalyst for Direct Methanol Fuel Cells and Its Evaluation by DFT

“…MEAs were fabricated adopting the procedure described elsewhere . In brief, both anode and cathode comprise a backing layer, a gas-diffusion layer, and a reaction (catalyst) layer.…”

“…Experimental data were curve fitted with a Gaussian and Lorentzian mix-product function after subtracting Shirley background. Spin−orbit splitting and the doublet intensities were fixed as described in the literature . Relative intensities of the surface species were estimated from the respective areas of the fitted peaks.…”

Graphitic Carbon as Durable Cathode‐Catalyst Support for PEFCs

“…In order to analyse the formation of surface functional groups and their influence on the non-faradaic current, CV measurements are conducted with PEFC cathodes comprising Pt/Non-GrC and Pt/GrC as catalysts, during which nitrogen is fed to both anode and cathode and cycled between -0.5 and 0.5 V [48]. The cyclic voltammograms (capacitance curves) for PEFC cathodes comprising Pt/Non-GrC and Pt/GrC electrodes are presented in Figure 5.…”