Performance Study of Direct Ammonia Fuel Cell Based on PtIr/C Anode Electrocatalyst

Ammonia (NH3), a carbon-free hydrogen energy carrier, is a key green energy for decarbonization, because of its easier storage and transport properties compared with hydrogen, as well as its higher volumetric energy density, which makes it suitable as alternative fuel and renewable energy carrier.To study the performance of PtIr/C anode electrocatalyst as direct ammonia (gas) fuel cells (DAFC), a laboratory test device was used to investigate the performance of DAFC employing anion exchange membrane (AEM) at different operating temperatures.Electrocatalytic activity of the PtIr/C electrocatalyst and performance of DAFC were examined by electrochemical workstation, respectively.Furthermore, the effect of NH3-KOH concentration in anode fuel on ammonia oxidation reaction (AOR) activity was investigated.An on-line Fourier infrared (FTIR) gas analyzer was used to measure the ammonia concentration and spectra of cathode exhausted gas in DAFC.The results showed that the highest open circuit voltage (OCV) of 0.50 V and the peak power density of 3.2 mW•cm -2 were obtained in DAFC at 80 ℃.The increased OCV might be attributed to the synergistic benefits (electronic effects) between Pt and Ir in the Pt-Ir transition alloys, which resulted in a shift to the lower over-potential of AOR.The rise in peak power density was mainly due to the increase of temperature, which improved the desorption of intermediate adsorption species (Nads) from the electrocatalyst, as well as it enhanced the kinetics of AOR.The suitable NH3-KOH concentration could reduce the onset potential of AOR and improve the catalytic activity.Both gas content and FTIR spectrum of the DAFC cathode exhausted gas confirmed the presence of ammonia concentration in exhausted gas at different temperatures, which demonstrated that ammonia fuel crossed the membrane electrode assembly (MEA) to the cathode site.It was further observed that ammonia cross-over increased with temperature, which led to a degradation of the cathode Pt/C electrocatalyst and resulted in the decrease of the OCV and power density of the DAFC.In this paper, the theoretical basis of DAFC agreed well with the experimental data.To further improve the performance of DAFC, it suggested that a high quality AEM allowing hydroxyl ion passing through but prohibiting ammonia cross-over, should be developed.