(Invited) In Situ Characterization during Electrode Processing: The Role of Hidden Parameters

Abstract

Micron and nano-sized functional materials play a key role for future technologies that are currently developed in the field of energy conversion (electrolysers, fuel cells) and electrocatalysis (N2 fixation, CO2 reduction reaction). While new materials with outstanding properties are continuously developed, they rarely find their way into – urgently needed – large scale production and industrial applications.1 One reason for this are hidden parameters that occur during ink formulation, coating (and decal transfer), cell assembly, and operation. We propose the development of coherent workflows that help us to identify reliable correlations. These should be developed for each electrocatalyst, bridging synthesis, electrode and gas diffusion electrode (GDE) / membrane electrode assembly (MEA) fabrication, and testing. All information, including “negative” results like crack formation, delamination, structural ageing and dissolution, must be reported until the relevant hidden parameters are deciphered, and the design chain is understood. Then, materials and electrodes derived from complementary processes and exhibiting subtle variations in composition and structure, can be evaluated against each other.However, this implies to fill the “blackbox” between technical catalysts and electrochemical testing in flow cells, GDEs or MEAs, with quantitative data on powders, ink formulations and coating properties. In the past years, we developed a toolbox of methods that starts from key control characteristics for technical catalysts, i.e., Pt/C for polymer electrolyte membrane fuel cells, that thereon enable the in situ analysis of ink formulations and pastes during the dispersion process and at application concentration.2,3 This is followed by the assessment of the resulting coatings from large-area crack analysis down to the level of surface roughness and pore size characteristics.4 Finally, this input is connected with performance and stability testing results to enable the comparison of different materials, the assessment of structure property relations, and ultimately to establish inline process control during electrode manufacturing. In this contribution, the developed methods will be summarized and related to their current limitations and prospects, in particular for unraveling hidden parameters during electrode fabrication and MEA assembly as well as in line process control. Literature [1] Siegmund, Daniel; Metz, Sebastian; Peinecke, Volker; Warner, Terence E.; Cremers, Carsten; Grevé, Anna; Smolinka, Tom; Segets, Doris; Apfel, Ulf-Peter; Crossing the Valley of Death : From Fundamental to Applied Research in Electrolysis, JACS Au 1 (2021), 527 – 535.[2] Bapat, Shalmali; Segets, Doris; Sedimentation Dynamics of Colloidal Formulations through Direct Visualization : Implications for Fuel Cell Catalyst Inks, ACS Applied Nano Materials 3 (2020), 7384 – 739.[3] Bapat, Shalmali; Giehl, Christopher; Kohsakowski, Sebastian; Peinecke, Volker; Schäffler, Michael; Segets, Doris; On the state and stability of fuel cell catalyst inks, Advanced Powder Technology 32 (2021), 3845 – 3859.[4] Jaster, Theresa; Albers, Simon; Leonhard, Armin; Kräenbring, Mena-Alexander; Lohmann, Heiko; Zeidler-Fandrich, Barbara; Özcan, Fatih; Segets, Doris; Apfel, Ulf-Peter; Enhancement of CO₂RR product formation on Cu-ZnO-based electrodes by varying ink formulation and post-treatment methods, JPhys Energy 5 (2023), 024001.