Advanced electron paramagnetic resonance in chemical energy conversion: current status and future potential

New sustainable energy technologies are an important current research field that aims to address the global environmental challenge caused by our excessive reliance on fossil fuels. Underpinning this field is the concept of energy conversion, be it the transformation of light energy to electrical energy, in the case of photovoltaic devices, or to chemical energy, in the case of producing renewable ‘green’ fuels (like H₂, CH₄, and NH₃). These necessarily involve multi-electron transfer processes whose precise reaction mechanisms can be challenging to resolve. Electron paramagnetic resonance (EPR) is a non-invasive and versatile technique used to characterize systems containing unpaired electrons, such as transition metal ions and radicals, and as such, is uniquely able to study complex, multi-electron catalytic cycles. By integrating the principles of EPR and its application in energy conversion systems, this review summarizes how EPR enhances our understanding of complex catalysts and supports the development of these technologies. EPR facilitates the identification of paramagnetic sites, optimization of catalyst synthesis, elucidation of reaction mechanisms and kinetics, and monitoring of catalytic stability, thus enhancing catalytic activity and prolonging catalyst longevity. We offer a perspective on its current and future potential in developing energy conversion technologies.