Making Fuel Cells Work- Challenges
Authors: Rajalakshmi Natarajan 
Published: January 2022

Fuel cells are remarkable in their potential for efficiently converting the energy locked up in chemical bonds to electrical energy in a single step, extracting more useful energy from the same amount of fuel than any other known device. Though for more than five decades, they have been heralded for their potential as a cost efficient, environmentally friendly means to convert, this has not been realized so far to its full potential.

Fuel cell operations are complex and the state of affairs is partly due to the fact that it is easy to make a single working fuel cell in the lab, but building fuel cell stacks that generate useful power reliably, efficiently, and cheaply is another matter entirely. The challenge of making reliable, efficient fuel cells is rooted in the complexities of how they operate, which involves multiple chemical and physical interactions at the atomic level and at different time scales. Perhaps no advanced technology on the market today requires the scale, magnitude, and range of scientific, physical, and engineering knowledge that fuel cell technology requires.

One important contribution is being slowly recognized, is the purity of fuel and air in the gas feed. As these fuel cells take to the roads and are likely to be deployed not always in clean “laboratory”. Recently our CFCT research group has started to look at the effect of likely contaminants like So2, Chlorine etc., in the fuel and air on fuel cell performance and its mitigation possibilities. The approaches developed vary from developing alternative catalysts like mesoporous Pt, alternative supports other than carbon, use of various oxidizers in the stream, operation at various current densities etc.,

The performance degradation was more severe at higher SO2 concentrations. At 100 ppm SO2 in air the performance degraded by 91% at the same potential. The power loss of the fuel cell could not be recovered by externally polarising the PEFC at 1.6 V. However, a 15 minute treatment with 0.4% O3 in air showed almost a 100% performance recovery of the 100ppm SO2 contaminated fuel cell. The enhanced recovery of the fuel cell is related both to the chemical reaction of O3 with the adsorbed sulphur contaminant, and an increase of cathode potential during the electrochemical treatment. However, in the case of multicells stacks, the recovery mechanism can be attributed to both a direct and indirect chemical processes, where Pt reacts with the adsorbed sulfur leading to drop in catalyst utilization at low current density regions. This can also be directly associated to weak and strong adhesion of sulfur species with platinum. However at higher current densities, in the presence of H2O, this undergoes rapid hydrolysis to form H2SO4, leading to 100% recovery.

The performance of PEMFCs under the marine environment has also been studied for a longer duration and also the recovery mechanism of the PEMFC power pack after contamination. It has been observed that the NaCl is a major contaminant for PEMFC, compared to NOx and SOx, which are major contaminants for fuel cells operating in the in the land regions.

The various catalysts that are studied for impurity studies and durability are mesoporous Pt, mesoporous Pt-Ru, N doped graphene as support for Pt based catalysts etc., These results will be presented.

Figure 1