Insight into Interface Behaviors to Build Phase-Boundary-Matched Na-Ion Direct Liquid Fuel Cells

One of the targets associated with developing high-performance alkaline direct liquid fuel cells is to maximize the utilization of catalysts and minimize the limitation of anion materials that suffer from low ion conductivity and thermal and chemical instability. Herein, an ionomer-free and phase-boundary-matched Na-ion direct formate fuel cell (Na-DFFC) was reported to address this issue from the viewpoint of meeting interface transport behaviors for electrochemical reactions. A proof-of-concept phase-boundary-matched Na-DFFC including neither ionomers nor additional liquid electrolyte yields a peak power density as high as 45 mW cm–2, primarily because the dissociation and hydrolysis of formate on anode and the generation of NaOH on cathode enable electrodes to possess sufficient Na+ and OH–, thereby increasing the double-phase boundary density, leading to a high catalyst utilization. Additionally, a stable 60 min constant current discharge at 90 °C proves the conceptual feasibility of the high-temperature Na-DFFC. These results present a new scheme toward high-performance alkaline direct liquid fuel cells in terms of meeting all requirements of electrochemical kinetics and mass and charge transport characteristics.