Abstract
We have synthesized carbon-supported silver (Ag/C) nanobars by a simple surfactant-free hydrothermal method using glucose as the reducing reagent as well as the source of carbon in Ag/C nanobars. Physicochemical characterization of the materials was performed by X-ray Diffraction (XRD), field emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The XRD pattern confirmed the presence of a pure metallic silver phase. No carbon phase was detected, which indicates that the carbon exists mainly in the amorphous form. The electrocatalytic activity of Ag/C in different electrolyte solutions such as 0.5 M NaOH, 0.5 M NaOH + 1 M ethanol (EtOH), 0.5 M NaOH + 1 M ethylene glycol (EG), and 0.5 M NaOH + 0.01 M NaBH4 (sodium borohydride) was studied by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronoamperometry (CA) study. Alcohol tolerance of the catalysts was also established in the presence of ethanol and ethylene glycol. The forward-to-backward current ratio from cyclic voltammetry (CV) study of Ag/C-20 (20 h) in 0.5 M NaOH + 1 M ethanol solution at 100 mV s−1 scan rate is 4.13 times higher compared to that of Ag/C-5 (5 h). Hence, Ag/C-20 is a better candidate for the tolerance of ethanol. In the presence of ethylene glycol (1 M) in 0.5 M NaOH solution, it is obtained that the forward-to-backward current ratio at the same scan rate for Ag/C-20 is lower than that in the presence of ethanol. The durability of the catalyst was studied by chronoamperometry measurement. We studied the electrochemical kinetics of Ag/C catalysts for borohydride oxidation in an alkaline medium. The basic electrochemical results for borohydride oxidation show that Ag/C has very well strength and activity for direct borohydride oxidation in an alkaline medium. The reaction of borohydride oxidation with the contemporaneous BH4−. hydrolysis was noticed at the oxidized silver surface. Among all the synthesized Ag/C catalysts, Ag/C-20 exhibited the best electrocatalytic performance for borohydride oxidation in an alkaline medium. The activation energy and the number of exchange electrons at Ag/C-20 electrode surface for borohydride electro-oxidation were estimated as 57.2 kJ mol−1 and 2.27, respectively.
Highlights
Over the last few decades, very expansive platinum (Pt) group metals were commonly used as electrocatalysts in energy devices due to their high conductivity and less corrosion
Even though both direct methanol fuel cell (DMFC) and direct borohydride fuel cell (DBFC) can overcome the difficulty of hydrogen storage, DBFC is far better than DMFC in case of power performance, electrochemical activity, capacity value, and theoretical open-circuit voltage at a normal temperature [8]
We guess that the growths of Ag/C nanobars were controlled by following ways: (i) low concentration of Ag+ ions controlled by silver sulfide which smooth the way for anisotropic development of silver nano-nuclei and (ii) coated layer of carbon further restricts the radial growth to form the 1D structure of Ag/C
Summary
Over the last few decades, very expansive platinum (Pt) group metals were commonly used as electrocatalysts in energy devices due to their high conductivity and less corrosion. It is already mentioned that platinum group metals and their alloys have colossal use as electrocatalysts for borohydride oxidation in energy devices like direct borohydride fuel cells. To make cost-effective catalysts for fuel cells, non-platinum metals have been studied for borohydride oxidation. The. motivation of our work was the surfactant-free synthesis of 1D carbon-supported silver nanostructures using hydrothermal conditions and studies their electrochemical characterization for borohydride oxidation in alkaline solution for the promising application in alkaline borohydride fuel cells and alcohol tolerance. Stosevski et al [1] synthesized Ag catalysts via a four-electron pathway for oxygen reduction and borohydride oxidation in an alkaline medium They reported the value of activation energy in 2 M NaOH + 0.03 M NaBH4 solution is 35 kJ mol−1. We obtained better BOR kinetics of Ag/C catalysts in 0.5 M NaOH + 0.01 M NaBH4 than that reported by Stosevski’s group
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