In this work, precious metal and spinel oxide bifunctional catalyst were prepared. 20 wt% Pt was deposited on commercial carbon (C65) by chemical reduction of hexachloro-platinic acid in formaldehyde at 80°C for 1 h. MnCo2O4 (MCO) and NiCo2O4 (NCO) Spinel were synthesized by hydrothermal (HT) and hard template (SS) methods. The structural characterization of the as-prepared catalysts was performed by means of XRD, SEM/EDX and TEM. Average size of as-prepared oxide particles was estimated to approximately 28, 100, 300 and 500 nm for HT-MCO, HT-NCO, SS-MCO and SS-NCO catalysts, respectively. Gas diffusion electrodes (GDE) with catalyst loading of 1 mgcat cm-2 were fabricated by airbrush spraying. Contact angle of electrode/electrolyte interface was measured for 100 h at room temperature and 30% RH. The electrochemical activity of commercial Pt/C and spinel-based GDE for ORR and OER were studied by cyclic voltammetry (CV) under half cell condition. The EL-Cell (ECC-Air) and coin cell (CR2032) were manufactured by assembling a Zn foil as active electrode, a glass fibre separator and a GDE. The cell performance was evaluated by U-I polarization at 1-100 µA cm-2 for 1‑3 h charge/discharge cycle. A preliminary screening of catalysts in terms of activity and stability was conducted in EL-Cell with dry air at RT. At 50 µA cm-2, comparison of charge/discharge kinetics of the different catalysts over 5 h/cycle is shown in fig.1a. An effect of addition of water in the IL was studied at 100 µA cm-2 in ambient air (30% RH at 22°C), 24 h/cycle for one month (fig.1b). The best system was HT-MCO that was further investigated under coin cell (CR2032) condition (Zn || ChAcO + 30 wt% H2O + 0.01 M Zn AcO || MnCo2O4/C65). At 100 µA cm-2, an energy and columbic efficiency of 50 and 100% was calculated for the 3 h cycle, respectively. The same cell was successfully tested in ambient air (RT, 30% RH) for 700 h (140 cycles) at 50 µA cm-2. Average cell voltage was 0.75 V (discharge) and 1.9 V (charge). A discharge specific capacity of 725 mAh gZn-1 was achieved at 100 µA cm-2.
1. M. Kar, T. Simons, M. Forsyth, and D. MacFarlane, Phys. Chem. Chem. Phys., 16, 18658, (2014).