RAPID COMMUNICATIONNanoporous Ag and Ag–Sn anodes for energy conversion in photochemical fuel cells
Graphical abstract
Highlights
► Porous Ag–Sn catalysts were prepared and studied for energy conversion. ► The highest current density obtained was 155 mA/cm2 for porous Ag anode. ► The porous Ag anode is UV-sensitive in ethylene glycol and ethanol. ► The electrochemically dealloyed Ag–Sn anode is UV-sensitive in ethanol.
Introduction
Direct methanol fuel cell (DMFC) has been studied extensively and considered as a possible power source for electric vehicles. However, the fuel, methanol, is toxic and volatile. Such properties make it unsuitable for many applications. Other organic fuels such as ethanol [1], [2], [3], [4], 1- and 2-propanol [5], [6], [7], [8], ethylene glycol [9], [10], dimethoxymethane and trimethoxymethane [11], [12] have been tested for direct liquid fuel cell applications. As one of the alternatives, ethanol is safer, easily produced and has more energy density compared to methanol (8.01 kWh/kg vs. 6.09 kWh/kg) [13]. It is of significant importance to develop new anode electrocatalysts for ethanol electro-oxidation in order to enhance the performance of direct ethanol fuel cells (DEFCs).
It has been reported that Pt-based bimetallic and trimetallic anode catalysts, such as Pt–Sn [14], Pt–Ru [15], [16], Pt–Ru–Sn [17], Pt–Pd–Au [18] and non-Pt based Pd–Ru [19], Ir3–Sn–C [20] have good electrocatalytic properties for ethanol electro-oxidation. Interestingly, anodes with porous structures were found to have activity for ethanol oxidation. Porous structured anodes can accelerate the anode reaction kinetics because of their high surface areas. It is reported that porous Pb–Ag anode [21], porous Ni–Pd or Co–Pd [22] have high performances in direct ethanol fuel cell.
In this work, we prepared nanoporous Ag and Ag–Sn electrocatalysts via chemical and electrochemical processing. The surface morphology of the porous Ag and Ag–Sn was examined by scanning electron microscopy (SEM). Their electrocatalytic behaviors were studied via cyclic voltammetry (CV). We made photochemical fuel cell using the porous Ag and alloy as the anodes, ethanol and ethylene glycol as the fuels. The open circuit voltages were measured under UV light.
Section snippets
Experimental
Ag–Sn wire with 1.5 mm diameter has the composition of 96 wt% Sn and 4 wt% Ag. The porous Ag–Sn anodes were made through chemical dealloying and electrochemical dealloying. For chemical dealloying, the Ag–Sn alloy was directly immersed into 5% hydrochloric acid for 24 h to form the porous anode. For electrochemical dealloying, the Ag–Sn alloy was selectively etched to increase the surface area in an electrolyte consisting of 5% hydrochloric acid, 75% ethanol and water. The pure Ag also has the
Morphological features
The morphologies of the original pure Ag and the electrochemically etched Ag are illustrated in Fig. 1. Fig. 1a reveals the surface of the Ag before the electrochemical treatment. It can be observed that the surface is relatively smooth with some parallel rolling marks from the mechanical machining. Fig. 1b–d exhibits the morphology of the Ag after electrochemical etching. Two types of morphological features are found on the Ag anode electrocatalyst. The small particles are found near the
Conclusions
We fabricated nanoporous Ag and Ag–Sn anode catalysts. The anodic current densities were measured for porous Ag, nonporous, chemically treated and electrochemically treated Ag–Sn anodes in ethanol containing electrolytes. The highest current density achieved is 155 mA/cm2 for the porous Ag anode. The electrochemically dealloyed Ag–Sn anode shows a better performance than the chemically dealloyed Ag–Sn anode in view of electrocatalysis. The porous Ag anode is UV-sensitive in ethylene glycol and
Acknowledgments
This research is supported in part by The Ohio Board of Regents through the URAF program of University of Toledo. LS is supported by the Doctoral Instrumentation Graduate Fellowship from University of Toledo.
Mr. Lusheng Su, joined the Department of Mechanical, Industrial and Manufacturing Engineering at The University of Toledo (UT) in 2009 as a Ph.D. graduate student. From 2008 to 2009, he worked for the Agricultural Development Bank of China, Xi'an, Shaanxi Province, P.R. China. He obtained his Master Degree of Engineering in 2008 and Bachelor Degree of Management in 2006 from Nanjing University of Science and Technology, Nanjing, Jiangsu Province, P.R. China. His major publications are on
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Mr. Lusheng Su, joined the Department of Mechanical, Industrial and Manufacturing Engineering at The University of Toledo (UT) in 2009 as a Ph.D. graduate student. From 2008 to 2009, he worked for the Agricultural Development Bank of China, Xi'an, Shaanxi Province, P.R. China. He obtained his Master Degree of Engineering in 2008 and Bachelor Degree of Management in 2006 from Nanjing University of Science and Technology, Nanjing, Jiangsu Province, P.R. China. His major publications are on nanomaterials processing, structure analysis, and thermoelectric property characterization.
Dr. Yong X. Gan joined the Department of Mechanical, Industrial and Manufacturing Engineering at The University of Toledo (UT) in 2007 as Assistant Professor. He was with Department of Mechanical Engineering at Cooper Union as Assistant Professor from September 2005 to August 2007. He received B.S. in Chemical Engineering in 1984 from Hunan University, Changsha, P.R. China. He received M.S. and D.Eng. in Materials Science and Engineering from Beijing University of Aeronautics and Astronautics (BUAA), Beijing, P.R. China in 1987 and 1992, respectively. He received M.Phil. in 2004 and Ph.D. in 2005 from Columbia University.