Basic Research Needs for Energy and Water: Report of the Office of Basic Energy Sciences Basic Research Needs Workshop for Energy and Water

Counterion Mobility in Ion-Exchange Membranes: Spatial Effect and Valency-Dependent Electrostatic Interaction

“…An even more challenging separation task is the selective transport of specific counterions from others with the same valency. Examples of such applications include harvesting lithium from produced water, recovering nitrogenous nutrients from waste streams, and removal of environmentally relevant oxyanions (e.g., H 2 AsO 4 – , H 2 BO 3 – , and H 2 PO 4 – ) from Cl – and HCO 3 – background ions. − ,, The current transport framework suggests that the spatial effect and electrostatic interaction are unable to adequately discern between counterions with identical valencies. Therefore, phenomena beyond those in the present transport model, such as ion-specific effects, would need to be engineered into the separation process and membrane development to realize such high-precision transport selectivity.…”

“…Improved selectivity in separations has been identified as a critical need for water, energy, and environment. − Fractionation of like-charged ions is required for several environmentally important separations. For example, the selective recoveries of nitrogenous compounds and orthophosphates from wastewaters with complex ionic compositions are vital to enable nutrient recycling (i.e., differentiating NO 3 – and H x PO 4 3– x anions from Cl – , HCO 3 – , and SO 4 2– and discriminating between NH 4 + and other cations of Na + , Ca 2+ , and Mg 2+ ). − Likewise, the precise removal of trace contaminants from much higher concentrations of background ions (such as Pb 2+ , Hg 2+ , Cd 2+ , and Cr 2+ cations from Na + , K + , Ca 2+ , and Mg 2+ and anions of H 2 AsO 4 – , H 2 BO 3 – , and SeO 4 2– from Cl – , HCO 3 – , and SO 4 2– ) is pivotal for water security. ,− The targeted extraction of Li + from other cations (e.g., Na + , K + , Ca 2+ , and Mg 2+ ) can realize the economic harvesting of lithium, a critical element in batteries, from unconventional sources, such as oil and gas produced water …”

“…) from Cl − and HCO 3 − background ions. [1][2][3]21,22 The current transport framework suggests that the spatial effect and electrostatic interaction are unable to adequately discern between counterions with identical valencies. Therefore, phenomena beyond those in the present transport model, such as ion-specific effects, would need to be engineered into the separation process and membrane development to realize such highprecision transport selectivity.…”

Linking Electric Double Layer Formation to Electrocatalytic Activity

“…25,26 Together, these effects modulate the interfacial reaction microenvironment, 27 and such effects are increasingly understood to play defining roles in sculpting reaction pathways. 28,29 The study and analysis of electric double layer formation arguably serves as a foundational direction for the field of colloidal science. From Helmholtz's pioneering studies in the 1850s 30 to contemporary investigations into diverse topics including colloid assembly, 31−33 soft materials, 34,35 and biology, 36−40 ionic assembly and electric double layer formation have been consistent threads connecting communities of researchers in colloid and interface science.…”

Molecular Properties and Chemical Transformations Near Interfaces

“…Chemistry rarely occurs in a homogeneous aqueous phase but, instead, occurs inside niches, within crevices, between surfaces, and at impurity sites involving interfaces between two or more phases of gases, liquids, or solids. Interfacially induced changes of molecular properties feed up at an operational level to a diverse range of chemical, biophysical, and applied environmental and energy systems including the following: the membrane pores for chemical separations and 2D crystals used for clean water generation, nanoconfinement chemistry, soft matter self-assembly, complex interfaces for heterogeneous catalysis for targeted energy reactions, intergranular corrosion in metals, aerosol and atmospheric particles, , and reaction rate acceleration in nanodroplets and microdroplets . However, at present, we lack the ability to accurately predict most molecular processes in such systems because interfacial and confinement effects violate our understanding of these same processes gained from bulk phase studies.…”