Kinetic and thermodynamic analysis of ammonia electro-oxidation over alumina supported copper oxide (CuO/Al2O3) catalysts for direct ammonia fuel cells.

In this work, ammonia electrooxidation (AEO) is studied to probe the electrochemical behavior of aqueous NH 3 as direct fuel by implication of gamma alumina supported copper oxide catalysts (CuO/Al 2 O 3). Precipitation and impregnation techniques are adapted to synthesize the substrate Al 2 O 3 , and loading of different ratios (1%, 2%, 3%, 4%) of active precursor i.e., CuO, respectively. Small average crystallite sizes (D Avg) in range of 1.46–6.76 nm and smaller particle sizes from micrographs proposed a superb activity of the catalysts. Modified GCE exhibited the excellent conductive properties towards standard redox probe K 4 [Fe(CN) 6 ] and KCl, displaying a high active electrochemical surface area of up to 0.0021 cm2. Current profiles in response to increase in scan rates, concentrations of ammonia and temperature have been observed in 0.1 M KOH, thereby estimating the thermodynamic and kinetic constraints of the AEO process. Attributed to the electroactive properties towards AEO, CuO/Al 2 O 3 is found to exhibit the desirable physiochemical properties owing to large oxidation current, large diffusion coefficient "D°" (3.6 × 10-9 cm2 s-1), large rate constant "ko" (1.2 × 10-5 cm s-1), large system entropy "ΔS" (-108 J K-1 mol-1), high change in enthalpy "ΔH" (72.3 J mol-1) and low activation energy "ΔG" (32.8 kJ mol-1). Resultingly, the oxidation of ammonia is found to be facile and robust by incorporation of CuO/Al 2 O 3 catalysts owing to large ko, ΔH and ΔH. This study opened a gateway towards eco-benign and economical efficient energy generation and viable market entry of direct ammonia fuel cells. • CuO/Al 2 O 3 microstructures are developed by typical precipitation and impregnation techniques. • Electrochemical understanding is built after fabricating the GCE with CuO/Al 2 O 3 catalysts. • Modified electrodes are tested for electrooxidation of ammonia in 0.1 M KOH electrolyte. • Kinetic and thermodynamic parameters are estimated varying the analyte concentration and temperature, respectively. • AEO is diffusion-controlled at low temperatures while activation-controlled at higher temperatures. [ABSTRACT FROM AUTHOR]