Abstract <p>Ion-transport selectivity in anion-exchange membranes (AEMs) remains a critical challenge for electrochemical systems for electrolysis and clean energy technologies. This is particularly true for the discrimination between hydroxide and competing anions such as bicarbonate and formate in the context of CO₂ electrolysis. The lack of selectivity between these species significantly impacts device performance through competitive transport of bicarbonate and formate over the desired hydroxide ions through anion-exchange membranes. Here, we demonstrate that interfacing a transferred single-layer graphene (SLG) coating with Sustainion X37-50 AEMs can dramatically enhance ion selectivity while having a smaller impact on desired hydroxide (OH⁻) ion-transport rates. We utilize permeation experiments and electrochemical impedance spectroscopy (EIS) to measure transport of hydroxide (OH⁻), bicarbonate (HCO₃⁻), and formate (HCOO⁻). Our SLG/AEMs can reduce bicarbonate transport by up to 92% and formate transport by up to 64% relative to baseline uncoated membranes, while only reducing hydroxide transport by 48&#xa0;percent. SLG/Sustainion membranes are found to result in 33% more selective membranes for OH⁻/HCOO⁻ and up to 548% more selective membranes for OH⁻/HCO₃⁻ when compared to bare Sustainion. Our findings demonstrate a promising strategy for minimizing product and reactant crossover in electrochemical CO₂ reduction systems through graphene-enhanced membrane selectivity.</p> Impact statement <p>Efficient ion-selective membranes are crucial for advancing sustainable energy technologies, particularly in CO₂ conversion and clean energy applications. This work demonstrates unprecedented ion selectivity through a simple graphene coating on conventional anion-exchange membranes, achieving a remarkable 548% improvement in hydroxide/bicarbonate selectivity under challenging high-concentration conditions. The selective transport properties arise from fundamental interactions between ions and the engineered membrane interface, leveraging the distinct transport mechanisms of different ionic species. This approach represents a significant advancement in membrane design, moving beyond traditional strategies that struggle to differentiate between ions of similar size and charge. The enhanced selectivity enables better control of local reaction environments, potentially improving the efficiency and selectivity of CO₂ conversion processes, fuel cells, and other electrochemical systems critical for decarbonization efforts. The simplicity of the graphene coating method suggests practical scalability, while the performance under concentrated conditions (1M) indicates robust operation under industrial conditions. This work provides new insights into controlling ion transport at interfaces and demonstrates a practical path toward more efficient electrochemical systems, contributing to broader efforts in sustainable energy technology development and carbon emission reduction strategies.</p> Graphical abstract <p>Single layer graphene enhances Sustainion anion exchange membrane selectivity between bicarbonate and hydroxide as measured by electrochemical impedance spectroscopy (EIS) and permeation testing.</p>