Thermodynamic Analysis of the Fuel Cells Efficiency-Thermodynamic Stability Approach

摘要

Energy conversion in fuel cells is performed by electrochemical and transport processes in the polymer electrolyte membrane, gas diffusion layers, catalyst layers, and in the pipes transporting hydrogen, oxygen, water and air into and out of the fuel cell. All these processes are analyzed from the point of view of phenomenological thermodynamics, which inherently describes their synergy (namely, the coupling between electric conductivity and diffusivity, electrochemical processes at the electrodes, etc.). The total efficiency of the energy transformation is discussed in two parts: Firstly, reflecting the fuel and waste transport; secondly, the chemical energy conversion into electricity. A cyclic process with constant enthalpy gives an adequate base for derivation of the fundamental relation between actual and theoretical efficiencies, temperatures differences, power density, etc. Moreover, the analysis of transfer coefficients for fuel (Hydrogen and Air) delivery and for waste (water) output yields a relation between activation losses end efficiency drop (Butler-Volmer equation). Comparisons of the analysis to experiments support the obtained general relations, which are transferable to all similar devices transforming the energy by the non-volumetric way (e.g., electrolyzer, photovoltaic cells, etc.)