Search

[Display omitted] • A theoretical description of protonic ceramic electrochemical cells (PCECs) is developed. • The effect of acceptor impurities in oxide membranes on the PCEC performance is elucidated. • The interaction of ionic defects with impurities can substantially affect the characteristics of PCECs. • The theoretical results are validated against the experimental data. • A pathway to improve the PCEC efficiency by proper dopant selection is proposed. Protonic ceramic electrochemical cells (PCECs) are promising energy conversion devices offering an efficient and environmentally friendly way to produce electricity and pure hydrogen. An important challenge in the development of PCECs is the enhancement of their performance through selection of optimal dopants for acceptor-doped oxide perovskites, commonly used as electrolyte membranes. In this work, we elucidate the implications of the interaction of protons and oxygen vacancies with acceptor impurities in oxide membranes for the performance of PCECs operating in the fuel cell and electrolysis modes. The analysis relies on our recent theoretical developments on fuel cell operation and oxide hydration, as well as on the proposed statistical theory of proton hopping conduction in acceptor-doped oxides. It is shown that the interaction between ionic defects and impurities can substantially affect the characteristics of proton-conducting membranes. General relationships between the output characteristics of PCECs based on membranes with proton and hole conductivity and the energies of acceptor-bound states of ionic defects are determined. It is established that trapping of protons and oxygen vacancies reduces both proton and hole currents and effective conductivities, thereby altering the dependences of the voltage and power density on current density. We demonstrate the possibility of tuning the power density and faradaic efficiency of PCECs by doping oxide membranes using acceptor impurities with varying defect trapping energies. The presented results contribute to understanding the functioning mechanisms of protonic ceramic fuel cells and electrolyzers, and provide new fundamental criteria for the selection of acceptor impurities for oxide membranes to develop high-efficient devices. [ABSTRACT FROM AUTHOR]

• A theoretical model of a fuel cell based on a proton-conducting membrane is developed. • A general equation for the effective fuel cell characteristics is derived. • The effect of hydrogen and air humidification on the fuel cell parameters is studied. • The total current density significantly depends on the fuel humidity. • Air humidification has a minor effect on the fuel cell output parameters. Proton ceramic fuel cells are promising electrochemical converters that produce electrical energy by oxidizing hydrogen. Understanding the impact of gas humidification on the characteristics of such fuel cells is pivotal for the development of high-performance devices. This study develops a theory elucidating the effect of hydrogen and air humidity on the output characteristics of fuel cells based on proton-conducting oxide membrane with mixed (proton and hole) conductivity. The theory is based on a self-consistent description of the strong non-uniform distribution of charge carriers inside the membrane and the variation of the gas phase composition along the fuel and air channels. It is shown that the total current density significantly and nonmonotonously depends on humidity of the inlet hydrogen fuel, while humidification of the inlet air has minor effect on the fuel cell characteristics. The influence of the anode and cathode gas humidity on the distribution of the various fuel cell parameters (current densities, resistivity, etc.) along the membrane is also determined. The obtained results reveal the possibility of enhancing the performance of the proton ceramic fuel cells with low polarization losses by optimizing the composition of the inlet hydrogen fuel. [ABSTRACT FROM AUTHOR]