Enhancing PEM water electrolysis efficiency by reducing the extent of Ti gas diffusion layer passivation
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Proton exchange membrane water electrolysis (PEM WE) suffers from several issues, such as the high cost and low stability of the electrolyser unit components. This is especially evident for an anode polarised to a high potential and in contact with an acidic membrane. Such a combination is detrimental to the vast majority of electron-conducting materials. Nowadays Ti (possessing a protective passive layer on its surface) is used as the construction material of an anode gas diffusion layer. Since the passivation layer itself is non-/semiconducting, an excessive degree of passivation leads to high surface contact resistance and to energy losses during PEM WE operation. This problem is usually solved by coating the Ti surface with precious metals. This leads to a further increase of the already very high cell investment costs. In this work an alternative method based on appropriate Ti etching (in acid) is presented. The (surface) composition of the samples treated was investigated using SEM, X-ray fluorescence and diffraction and photoelectron spectroscopy. TiHx was found in the subsurface layer. This was responsible for preventing excessive passivation of the Ti metal. The superior performance of the etched Ti gas diffusion layer (compared to non-etched) in a PEM water electrolyser was confirmed during an (> 100 h) experiment with current densities of up to 1 A cm− 2. Using the described treatment the surface contact resistance was substantially reduced and its increase during PEM WE operation was largely suppressed. As this method is very simple and cheap, it has tremendous potential for improving PEM WE process efficiency.
KeywordsPEM water electrolysis Titanium passivation Titanium hydride Photoelectron spectroscopy Surface contact resistance Etching
Financial support of this work by the Grant Agency of the Czech Republic within the framework of Project No. 15-02407J and by the Deutsche Forschungsgemeinschaft, Grant no. HA6841/2-1 and no. SU189/7-1, is gratefully acknowledged. Part of the material characterisation experiments was performed utilising instrumentation financed by the Operational Programme Prague—Competitiveness (CZ.2.16/3.1.00/24501) and the “National Program of Sustainability” (NPU I LO1613) MSMT-43760/2015.
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