Experimental Investigation of the Influence of Pressure on the Performance of Polymer Electrolyte Water Electrolysis Cells

Fluctuating electric energy production from renewable sources is increasing. While this is desired from an environmental point of view because production does not match consumption, storage is required to avoid curtailment [1]. Dynamically operable polymer electrolyte water electrolysis (PEEC) may be used to convert excess electric energy from fluctuating sources into chemical energy, i.e. hydrogen and oxygen [2]. For storage, transportation or methanation of hydrogen and optionally oxygen, pressure levels up to 300 bar, for mobility up to 800 bar are needed.

Conventional, mechanical compression of hydrogen to the above mentioned pressure levels is inefficient, noisy and many compression stages are required which cause high investment costs and intensive maintenance. In contrast, electrochemical compression in high pressure (HP) PEEC promises to be more efficient, silent and low maintenance. On the one hand theoretically higher pressure leads to higher thermodynamic voltages, while on the other hand it may decreases the transport losses due to smaller gaseous bubbles, especially at high current densities [3].

Experimental results of HP-PEEC up to several hundred bar are discussed, investigating the influence of HP on transport losses at high current densities. The evolution of the different overvoltages (kinetic, ohmic, mass transport), determined using high frequency resistance measurements and tafel extrapolation, is discussed as a function of gas pressure. In detail the influence of different porous titanium sinter current collector media on mass transport losses is discussed as function of temperature, pressure and current density. It is shown that there seems to be an optimum average pore diameter at about 10 µm (Fig. 1).

Literature:

[1] C. J. Barnhart, et al., Energy Environ. Sci., 6 2804-2810 (2013).

[2] F. Barbir, Solar Energy, 78(5) 661-669 (2005).

[3] S. A. Grigoriev, et al., International Journal of Hydrogen Energy, 34(14) 5986-5991 (2009)