Plasmonic Catalytic Layer for Visible-Light Enhanced Methanol Oxidation Reaction
Authors: Lin Chun-Ting , Huang Hung Ji , Chang Mao-Nan , Chen Po-Li , Hsiao Chien-Nan , Shiao Ming-Hua , Tseng Fan-Gang 
Published: February 2020

Methanol oxidation reaction (MOR) has been an important topic in electrochemical fuel cells [1]. However, the slow kinetics of MOR brings the bottleneck that directly limits the efficiency of direct methanol fuel cells (DMFCs). Traditionally, platinum (Pt) based alloys, e.g. PtRu, PtAu, PtCu, and etc., are used as the catalysts for MOR [2]. Aiming at enhancing the MOR, titanium dioxide and other semiconductors have also been introduced to the anodic design of DMFCs [3]. Many nano-composite have been proposed as the catalysts for MOR, including Pt-TiO2 [4], Pt-ZnO [5], Pt-WO3 [6] and etc..
In another field of physical chemistry, plasmonic catalysis has been a rising field in photochemistry for more than one decade [7]. Noble metals, e.g., gold (Au), silver (Ag), Pt are common candidates for plasmonic catalysis. Besides, nano-composites , e.g., Ag-SiO2, Au-TiO2, Au-SiO2, and etc., have also attracted enormous attentions. By utilizing metallic nanostructures and/or metal-semiconductor nano-composites, visible light can be harvested and transformed into chemical energy to trigger or enhance chemical reactions, e.g. water splitting [8], hydrogen dissociation [9], steam reforming of ethanol [10], degradation of ammonium [11].
In this paper, self-supported metallic nano-dendrites are proposed as plasmonc catalytic layer for visible-light enhanced methanol oxidation reaction. Besides, an extra facile fluoride assisted galvanic replacement was proposed to prepare self-supported Ag and Ag nano-dendrites on Si base. These structures can be achieved by simply immersing Si wafers into the mixture of AgNO3 (or HAuCl4) and buffered oxide etchant (BOE) under ambient conditions within 5 minutes [12, 13]. The prepared Au (or Ag) nano-dendrites were used to boost methanol oxidation reaction under visible-light illumination (AM 1.5G). Obvious photo-enhancement on the oxidation current (28%) was achieved on Au nano-dendrites. A comparative study was conducted by measuring the photo-enhancement under various illumination wavelengths. The best photo-response was found at 700 nm. Moreover, the self-supported Au nano-dendrites with various pore sizes and branch sizes not only provide high aspect surface area but also enable a broadband plasmonic enhancement.
In summary, we proposed a cost-effective and facile approach to prepare Ag and Au dendrites on Si base under ambient conditions. Both Ag and Au nano-dendrites show promising potential in plasmon enhanced methanol oxidation reaction. We expect these structures may soon find application in photo-electrochemical cells.
References:
[1] S. K. Kamarudin, et al., "Overview on the challenges and developments of micro-direct methanol fuel cells (DMFC)," Journal of Power Sources, vol. 163, pp. 743-754, 2007.
[2] H. Liu, et al., "A review of anode catalysis in the direct methanol fuel cell," Journal of Power Sources, vol. 155, pp. 95-110, 2006.
[3] K. Drew, et al., "Boosting Fuel Cell Performance with a Semiconductor Photocatalyst: TiO2/Pt-Ru Hybrid Catalyst for Methanol Oxidation," The Journal of Physical Chemistry B, vol. 109, pp. 11851-11857, 2005.
[4] C.-T. Lin, et al., "A simple fabrication process of Pt-TiO2 hybrid electrode for photo-assisted methanol fuel cells," Microelectronic Engineering, vol. 88, pp. 2644-2646, 2011.
[5] C.-Y. Su, et al., "Fabrication of High-Activity Hybrid Pt@ZnO Catalyst on Carbon Cloth by Atomic Layer Deposition for Photoassisted Electro-Oxidation of Methanol," The Journal of Physical Chemistry C, vol. 117, pp. 11610-11618, 2013/06/06 2013.
[6] S. Jayaraman, et al., "Synthesis and characterization of Pt-WO3 as methanol oxidation catalysts for fuel cells," Journal of Physical Chemistry B, vol. 109, pp. 22958-22966, Dec 2005.
[7] Z. Xuming, et al., "Plasmonic photocatalysis," Reports on Progress in Physics, vol. 76, p. 046401, 2013.
[8] D. B. Ingram and S. Linic, "Water Splitting on Composite Plasmonic-Metal/Semiconductor Photoelectrodes: Evidence for Selective Plasmon-Induced Formation of Charge Carriers near the Semiconductor Surface," Journal of the American Chemical Society, vol. 133, pp. 5202-5205, 2011/04/13 2011.
[9] S. Mukherjee, et al., "Hot Electrons Do the Impossible: Plasmon-Induced Dissociation of H2 on Au," Nano Letters, vol. 13, pp. 240-247, 2013/01/09 2013.
[10] H. J. Huang and B.-H. Liu, "Plasmonic energy transformation in the photocatalytic oxidation of ammonium," Catalysis Communications, vol. 43, pp. 136-140, 2014.
[11] H. J. Huang, et al., "Plasmonic photocatalytic reactions enhanced by hot electrons in a one-dimensional quantum well," AIP Advances, vol. 5, p. 117224, 2015.
[12] C.-T. Lin, et al., "A facile approach to prepare silicon-based Pt-Ag tubular dendritic nano-forests (tDNFs) for solar-light-enhanced methanol oxidation reaction," Nanoscale Research Letters, vol. 10, pp. 1-8, 2015/02/18 2015.
[13] C.-T. Lin, et al., "Rapid fabrication of three-dimensional gold dendritic nanoforests for visible light-enhanced methanol oxidation," Electrochimica Acta, vol. 192, pp. 15-21, 2016.