A guide to ion separations for the global energy transition

Ion separation materials and processes play a crucial and easily overlooked role in emerging technologies for energy conversion and storage, critical resource recovery, and environmental protection. However, many emerging separation problems exceed the capabilities of currently available materials. Accelerating research in this area thus has high potential to advance economic and environmental sustainability. Efforts to develop more selective materials are hindered by an incomplete understanding of microscopic ion transport and sorption behavior as well as disparate terminology and conventions for describing a single phenomenon among different fields. This perspective offers a coherent framework for rationalizing ion separation behavior based on a rigorous review of electrolyte physical chemistry. After surveying the scope of relevant ionic species and electrolytes, it consolidates their key physical-chemical properties into a “periodic table of ions” that provides a useful heuristic for understanding ion separations. It also comments on the prospects for different material and process design strategies and offers a set of best practices for maximizing the rigor and transferability of new ion separations research.