**Author details**

ZCS – Zero current switching

358 New Developments in Renewable Energy

C – Equivalent electrical capacitance (F)

Jmax – Maximum current density (A/cm2)

ENernst – Thermodynamic potential

PO2 – Oxygen partial pressure (atm)

PH2 – Hydrogen partial pressure (atm)

RM – Equivalent membrane resistance (Ω)

T – Cell operating temperature (K)

Vact – Activation voltage drop (V)

Vohmic – Ohmic voltage drop (V)

Vcon – Concentration voltage (V)

ξi, ψ – Parametric coefficients

λ – Membrane thickness (μm)

fr – Resonant frequency (Hz)

wr – angular frequency (rad/s)

Zr – Resonant impedance (Ω)

Lr – Resonant tank inductor (H)

Cr – Resonant tank capacitor (F)

and financial support needed to conduct this research.

The authors would like to thank the Institute of Systems and Robotics of Porto University (ISR-Porto) and Foundation for Science and Technology (FCT), which provided them the conditions

Q – Quality factor

**Acknowledgements**

A – Cell active area (cm2)

n – Number of cells in stack

RC – Contact resistance (Ω)

Maria Teresa Outeiro1\* and Adriano Carvalho2

\*Address all correspondence to: touteiro@isec.pt

1 Department of Electrical Engineering, Institute of Engineering of Coimbra, Institute of Systems and Robotics – Porto, Portugal

2 Department of Electrical and Computer Engineering, University of Porto, Institute of Systems and Robotics – Porto, Portugal
