<p>Alkali-free direct formate fuel cells employing a cation exchange membrane offered a simplified cell configuration; however, their performance remained constrained by a limited understanding of ion transport and cathode water management. This study systematically evaluated the roles of cathode catalyst selection and gas diffusion layer wettability in direct formate fuel cells using a cation exchange membrane and a cation-conducting ionomer. Power generation characteristics showed that platinum supported on carbon consistently exhibited higher performance than palladium supported on carbon, particularly at elevated formate concentrations, indicating that the oxygen reduction reaction predominantly proceeded via a proton-involved, water-producing pathway. Constant-current operation combined with fuel composition analysis confirmed that protons acted as the dominant charge carriers, whereas sodium ions induced localized alkalization and accelerated cathode flooding in hydrophilic configurations. Replacing a hydrophilic gas diffusion layer with a hydrophobic one markedly enhanced water removal, suppressed sodium-ion-driven alkalization, and extended the discharge duration by more than three times. The hydrophobic gas diffusion layer also preserved proton-dominated ion transport without significantly altering formate crossover behavior. Overall, these results indicated that platinum supported on carbon functioned as a more effective cathode catalyst for alkali-free direct formate fuel cells using a cation exchange membrane and a cation-conducting ionomer, and that hydrophobic cathode gas diffusion layers played a critical role in stabilizing oxygen transport and sustaining long-term performance. The findings provided practical design guidelines for advancing compact, additive-free direct formate fuel cell systems toward sustainable energy applications.</p> Graphical Abstract <p></p>