The enhancement of formic acid electrooxidation (FAO) has garnered significant attention from researchers striving to develop efficient fuel cells. This study focuses on the improvement of FAO at platinum (Pt) and nickel oxide (NiOx) nanoparticle-based catalysts, utilizing urea derivatives as blending fuels. Blending formic acid with varying proportions of these urea derivatives has demonstrated notable enhancements, highlighted by a favorable negative shift of the onset potential (Eonset) and increased peak current density, concurrently reducing harmful CO poisoning reactions.
Among the urea derivatives tested, phenyl urea (PU) exhibited the most substantial effect on boosting formic acid's direct electrooxidation. Specifically, the addition of PU resulted in approximately 150 mV negative shift of Eonset and minimal CO formation. This enhancement is attributed to the inductive effect of the phenyl group on the urea, which facilitates the formation of 8-membered rings via hydrogen bonding with the formate ion—thereby enriching the electrode/electrolyte interface.
The research conducted by authors including A. M. Saada and M. E. Ghaith highlights the pressing need for sustainable energy sources to mitigate the adverse environmental impacts of fossil fuels. Technological advancements push researchers to explore efficient renewable energy systems, such as fuel cells, which have gained traction due to their high energy density and low operating temperatures compared to traditional power sources.
Direct liquid fuel cells (DLFCs) have emerged as promising candidates for renewable energy production, particularly due to their practical advantages over conventional hydrogen fuel cells. One such example is the direct formic acid fuel cell (DFAFC), recognized for its theoretical open circuit potential of 1.45 V, energy density of 1.4 kWh/kg, and low crossover rates. Despite its potential, DFAFCs suffer from issues of stability and catalytic activity, particularly due to the interference posed by CO produced during the oxidation of formic acid at Pt catalysts.
To overcome these challenges, researchers have introduced strategies to boost the oxidation of small organic molecules, like formic acid, through the addition of another organic molecule. Notably, the strategic blending of fuels can alter their preferential orientation at active sites on the anodic catalyst. This alteration may reduce the undesired oxidation pathways leading to CO formation, allowing for improved catalytic performance.
The methodology of the study involved conducting electrochemical measurements such as cyclic voltammetry (CV), chronoamperometry (CA), and linear sweep voltammetry (LSV) on Pt and Pt-NiOx modified glassy carbon (GC) electrodes. The creation of these electrodes involved specific preparation techniques, including electrodeposition of Pt nanoparticles and nickel oxide on the GC substrate. The findings suggest the addition of urea not only shifts the onset potentials to more favorable positions but also increases the current density for direct oxidation.
The results suggest compelling conclusions about the electrooxidation of formic acid. Notably, phenyl urea was particularly effective, enhancing the oxidation process with minimal CO generation. The study posits the possibility of forming hydrogen bonds between urea derivatives and formic acid, supporting the idea of forming more stable and reactive structures at the catalyst surface. These assumptions are reinforced by density functional theory (DFT) calculations, which revealed significant stability differences when comparing the binary fuels to their individual substrates.
Overall, these findings highlight the pivotal role urea derivatives can play in enhancing the electrooxidation of formic acid, offering new insights for improving the efficiency of direct liquid fuel cells. The author's work marks a significant advancement, showcasing the potential of blending various organic fuels and their derivatives to optimize fuel performance and pave the way for broader applications of sustainable energy technology.