Large scale storage of surplus electrical energy in the form of chemical bonds, especially hydrogen, is an attractive solution to level out fluctuations in renewable energy supply. Electrochemical water splitting is a promising method for the conversion of electrical energy into hydrogen. The overpotential that is necessary to drive the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) at the cathode and anode, respectively, makes the use of efficient electrocatalysts necessary. Therefore, enormous efforts are currently devoted to the development of highly active catalysts for both reactions. The often labile nature of highly active sites and the poor adhesion on the electrode surface especially of powder based electrocatalysts hamper their implementation in alkaline water splitting. Thus, new approaches to stabilize catalytically active materials on electrode surfaces are highly needed. We present two novel concepts which focus on the stabilization of powder based electrocatalysts on electrode surfaces and go beyond the current state of the art catalyst immobilization in organic polymeric binder materials.<br/>The first is based on embedding the catalytically active material in a stabilizing and conductive carbon matrix derived by thermal carbonization of polybenzoxazine networks (Barwe et al. ChemSusChem (2017) 10, 2653). The highly stable immobilization of NiFe LDH under highly demanding electrolysis conditions revealed possible structural changes of this class of materials when stressed at high current densities, high base concentration and high temperature (Andronescu et al. Angew. Chem. Int. Ed. (2017) 56, 11258).<br/>The second is an innovative approach for attaining very stable catalytic films with self-healing capability based on in-situ self-assembly of catalyst nanoparticles during active electrolysis (Barwe et al. Angew. Chem. Int. Ed. (2017) 56, 8573). In this approach, the catalyst nanoparticles are directly added to the electrolyte forming a suspension that is pumped through a running electrolyser cell. Nanoparticles with negatively charged surfaces adsorb on the anode, while those with positively charged surfaces adhere to the cathode governed by electrostatic forces. Importantly, self-assembled catalyst films possess self-healing properties as long as a sufficient amount of the catalyst particles are present in the electrolyte, leading to stable cell voltages at high current densities for more than three weeks.

Two Janus faces in electrocatalysis: Activity versus stability of transition metal based electrocatalysts

255th National Meeting (2018)

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