Biryukov G.M., Osina M.A., Bogdanovskaya V.A., Radina M.V.

National Research University "Moscow Power Engineering Institute", Russia

 

INFLUENCE OF CARBONIC CARRIER CHARACTERISTICS ON SUSTAINABILITY OF FUEL CELL CATHODE CATALYST

Consumption of electric power is increasing progressively. However, conventional energy sources in such areas as aviation, space, submarine service, etc. including decentralized, emergency and standby energy supply are unable to cover requirements of consumer. Consequently, to develop autonomous energy systems, or electrochemical energy facility, is required. These facilities consists of electrochemical generators, system to store and prepare fuel and oxidizer, electric transducers, system to utilize generated heat. Electrochemical generator includes as follows: fuel cell (FC) stack, facility to provide fuel and oxidizer, and withdraw reaction product and heat, automation system to regulate and control temperature (thermostatic control), power and other parameters of the system [1].

The main part of FC is a membrane electrode assembly (MEA) that consists of electrolyte, cathode and anode layers (active layers). Active layer is a suspension (catalytic “ink”) that covers membrane surface or gas diffusion layer. This catalytic “ink” generally comprises three components as follows:

·                    catalyst with carbonic carrier: nanoparticles of metal phase coated on dispersive carbon material;

·                    solvent: water diluted spirits;

·                    ionomer solution: solid polymer electrolyte – Nafion that is solved in a mixture of low-molecular aliphatic alcohols.

Fig. 1 represents principal diagram of hydrogen air FC.

Fig. 1. Principal diagram of the device layout of H2-air FC:

MEA – membrane electrode assembly; FP – flow plates; НE – heating elements; CP – clamping plates; FS – fluoroplastic shims; ТC – thermocouples.

One of the critical issues that prevents to develop and implement FC as a source of current in various power facilities is a degradation of cathode catalyst [2]. This leads to decreasing of its electrochemically active surface (determined with a cyclic voltammogram (CVA)), activity (determined by voltage upon voltage density 0.5 A/cm2 on a discharge characteristic), and degradation of carbonic carrier (across potential cycling). Method of accelerated stress-testing [3] allows to determine specifications of degradation processes in FC hydrogen-air.

The research of synthesized catalyst 20 % mass Pt on carbon nanotubes (CNT) was conducted. MEA with an area of 25 cm2 with cathode active layer based on catalyst 20 % Pt/C nanotubes was produced; cycling in the various potential ranges was conducted (Fig. 2, 3).

Fig. 2. CVA of 20 % Pt/CNT cathode catalyst in the MEA

Fig. 3. Results of accelerated stress testing of the MEA
This shows that catalyst based on CNT is represented as more stability in comparison with commercial Pt/C catalyst where the carrier is a carbon black. Therefore, one of the directions to increase stability of catalyst systems is use of CNT as a carrier.

 

 

 

References

1.                Korovin N.V. Fuel cells and electrochemical facilities. – М.: Publishing House МEI, 2005. – 280 p.

2.                Tarasevich M.R., Korchagin O.V. Rapid diagnostics of characteristics and stability of fuel cells proton-conducting electrolyte // Russian Journal of Electrochemistry. 2014. V. 50. № 8. P. 737-750. 

3.                Kuzov A.V., Tarasevich M.R., Modestov A.D., Korchagin O.V. Degradation processes in hydrogen-air fuel cell as a function of the operating and composition of membrane-electrode assemblies // Russian Journal of Electrochemistry. 2016. V. 52. № 7. P. 705-715.