**2.2 Instruments and materials**

Both voltammetric and chronoamperometric measurements were performed using Autolab general purpose electrochemical system (Ecochemie, Netherland). A lab-constructed singlecell system with temperature control, gas flow rate and pressure control, and liquid flow rate and pressure control constructed was used for the measurements of fuel cell performance.

All chemicals and materials were used as received without further purification. All solutions were prepared from methanol (>99.9%, Aldrich) or KOH (>85%, Aldrich) with deionized water (18.2 M cm). Unsupported electrocatalysts were used in voltammetric and chronoamperometric measurements, including Pt black (Alfa, S.A. typically 27 m2 g-1), Pd black (Alfa, S.A. typically 20 m2 g-1) and Ag nanopowder (Alfa, 20-40 nm). Carbon supported Pt (Fuel Cell Store, 60 wt% Pt/C) and carbon supported Pd (Sigma-Aldrich, 30

Investigations of Intermediate-Temperature Alkaline Methanol

electrochemistry for Pt electrode at elevated temperature.


the pH value of the reaction medium as follows:

**Current / A**

temperature.

Fuel Cell Electrocatalysis Using a Pressurized Electrochemical Cell 165

overpotential on Pt is neglected. This value is very close to our measured value (−1.1 V). This agreement between the calculated value and measured value suggests that the Ag/AgCl electrode satisfactorily functions as the internal reference electrode in hydroxide solution. This is also supported by the characters of the hydrogen and oxygen


 20 <sup>o</sup> C 40 <sup>o</sup> C 60 <sup>o</sup> C 80 <sup>o</sup> C 105 <sup>o</sup> C 130 <sup>o</sup> C 150 <sup>o</sup> C

(2)

(3)

**Potential / V vs Ag/AgCl**

Fig. 2. Cyclic voltammograms for a high-surface Pt-coated Au disk electrode of 0.5 mm diameter in 0.5 mol dm-3 KOH at a scan rate of 50 mV s-1 as a function of reaction

shifted by around 40 mV as the temperature is increased from 20 to 150 °C.

2

2

*H*

of *R* and *F* into Equation 2 results in its simplification as follows:

*<sup>o</sup>* 2.303

To further evaluate the suitability of using the Ag/AgCl electrode as the internal reference in the wide temperature range of our interest, the cyclic voltammograms for a high-surfacearea Pt-coated Au disk in 0.5 mol dm-3 KOH solution equilibrated with 200 psi H2 are measured and shown in Fig. 3. The positive-going scans are characteristic of fast-rising currents at lower overpotentials, followed by slow-rising currents and limiting currents at higher overpotentials. These characteristics are similar to literature results for H2 oxidation at Pt electrodes in aqueous base solution (Bao & Macdonald, 2007; Schmidt et al., 2002). Increasing reaction temperature clearly increases the limiting currents. These changes are mainly caused by the concentration changes of dissolved H2 as a function of the temperature. The potential value at zero current (*EH2,I=0*) measured in Fig. 3 is negatively

The reversible potential of hydrogen reaction depends upon the reaction temperature and

*RT <sup>E</sup> pH <sup>F</sup>*

where *T* is in K. Substituting pH=13.69 (corresponding to 0.5 mol dm-3 OH¯) and the values

<sup>3</sup> 2.7 10 *<sup>o</sup> E T <sup>H</sup>*

wt% Pd/C) were used for the preparation of gas diffusion electrodes with carbon-cloth as the diffusion layer. All gases used were of research grade.

### **2.3 Electrochemical measurements**

During the measurements of base voltammograms and methanol electrooxidation, highpurity nitrogen was introduced into the electrochemical cell to inhibit vaporization of the liquid phase at elevated temperature, and gas-phase pressure was set at 300 psi unless otherwise stated. Background voltammograms were measured in 0.5 mol dm-3 KOH at 50 mV s-1. All methanol oxidation experiments were carried out in 0.5 mol dm-3 KOH + 0.5 mol dm-3 methanol. Steady-state voltammograms for the methanol oxidation were recorded at a scan rate of 10 mV s-1. The measurements of the chronoamperograms were performed by stepping potential from -1.1 V where no methanol oxidation occurs to a given value where methanol is oxidized. For the purpose of comparison, the oxidation of hydrogen was investigated under similar conditions by introducing high-purity hydrogen into the electrochemical cell to equilibrate with the solution of 0.5 mol dm-3 KOH solution at 200 psi. All oxygen reduction experiments were carried out in 0.5 mol dm-3 KOH solution equilibrated with 300 psi high purity O2. To investigate the electrochemical oxidation of CO, high purity CO was introduced into the electrochemical cell with the pressure set at 300 psi.
