Complex Solid Solutions and High Entropy Materials for Energy Conversion Devices

Complex multicomponent alloys, i.e., complex solid solutions (CSS), and their particular case – high entropy alloys (HEA), have gained a lot of attention due to their unique properties. Besides their extraordinary mechanical and chemical properties such as high strength-to-weight ratio, fracture resistance, resistance to oxidation, etc., they also possess unique structural properties that make them attractive for applications in catalysis and energy storage. Namely, due to the higher number of component elements and thermodynamic and kinetic stabilization due to high entropy effects, they can retain a large number of different active sites on the surface. The large number and wide range of binding energies open numerous possibilities for the identification and manipulation of binding energies, and potentially, the more efficient and tunable catalysis of multistep or branching reactions, or potentially, the creation of multifunctional catalysts. Nonetheless, in order to fully exploit their potential, many aspects of their behavior need to be understood, particularly their behavior under operational conditions, stability under relevant conditions for real-world applications, observation of activity, stability and selectivity trends, etc. Therefore, research into their electrocatalytic behavior, especially at fundamental levels – determining the kinetic current densities, effective surface areas, active sites and their distribution, degradation mechanisms, phase separation and leeching, etc, requires careful assessment. In this regard, understanding their behavior under operando conditions is of particular interest. It is well established that multicomponent oxide materials show exceptional (electro)catalytic and pseudocapacitive properties as well, generating a large interest in their application as catalysts and supercapacitor active materials. Considering the huge number of degrees of freedom available for their design the systematic investigation of such complex systems requires significant inputs of both theory and possibly, machine learning for their better understanding. The significance of high-entropy alloys and oxides as potential catalysts thus lies in their capacity to overcome traditional limitations in catalysis, offering enhanced performance, stability, and versatility for a wide range of chemical reactions and industrial processes. Ongoing research and development in this area are focused on unlocking the full potential of HEAs and complex multicomponent catalysts in general, making them particularly interesting in the advancement of sustainable and efficient electrocatalysts. This collection aims to showcase the impact of high entropy materials on the performance and stability of energy conversion devices.

Keywords: energy transition; renewable energy; energy transition; complex solid solutions; high entropy alloys; electrolyzers; fuel cells; supercapacitors; electrocatalysis; reaction intermediate binding energy