The toluene-methylcyclohexane organic hydride has been expected to be a candidate of the hydrogen energy carrier system for the effective utilization of renewable energy. We have developed an electrocatalyst for the toluene electro-hydrogenation electrolyzer. However, hydrogen evolution as the side reaction decreases the current efficiency by inhibiting the toluene mass transfer. In this study, we demonstrated the effect of the toluenemethylcyclohexane chemical-hydrogenation by the loading of Pt nanoparticles in the carbon-paper as a porous flow-field. The loaded Pt in the flow-field functioned as the toluene hydrogenation catalyst with the generated hydrogen gas. This simultaneous functioning of chemical-and electro-hydrogenation in the flow-field and the catalyst layer was designed to enhance the overall apparent current efficiency. Based on the electrochemical measurement, the Pt-loaded carbon paper flow-field showed an outstanding enhancement of the current efficiency without a decrease in performance for the Pt loading from 0.5 to 0.02 mg cm −2. The conversion from toluene to methylcyclohexane by a one-through operation of the electrolyzer achieved 92-96% by using the Pt-loaded carbon paper flow-field. Simultaneously, the cell voltage was 1.92 V at 0.4 A cm −2 for a 0.5 mg-Pt cm −2 loaded carbon paperused membrane cathode assembly based on linear sweep voltammetry.
Introduction Usage of renewable energy has been got a lot of attention to find a way to sustainable society against environment and energy issues. To supply of renewable energy on demand, large-scale of energy storage and transportation is needed. Hydrogen is expected to apply for the energy storage and transportation. We have been paid attention the organic hydride, especially toluene (TL)-methylcyclohexane (MCH) system as a carrier for energy storage and transportation, because it is higher energy density than hydrogen with easy to handle, and can use the petroleum infrastructure in existence. Direct electrohydrogenation of TL applied polymer electrolyte fuel cell and industrial electrolysis technologies is a simple process with high energy conversion efficiency [1-3]. In this process, hydrogen is a byproduct to decrease current efficiency of chemical hydrogen. Therefore, the suppression of hydrogen evolution is needed. In this study, we have investigated the effect of catalyst-loaded backing of electrocatalyst layer on the polarization and the current efficiency with low concentration TL feed to improve cell performance. Experimental Mixture of ethanol, H2PtCl6・6H2O and H2O ( the ratio is 3.0 : 0.3 : 1.0 ) were used as a precursor of Pt catalyst on a carbon paper (35BC, SGL Carbon). The paper was dipped in the mixture, and dried at 60oC for 10 min. Then it was heated at 240oC for 6 h in nitrogen atmosphere to prepare Pt loaded cathode backing (called CPt). The carbon paper backing with no Pt is called Cnon-Pt. An anode was the DSE® (De Nora Permelec Ltd.) electrode for oxygen evolution. A cathode was 0.5 mg cm-2 of PtRu/C (TKK) coated on a CPt or Cnon-Pt, and it was hot-pressed(120oC, 0.27 MPa) on a Nafion® 117(DuPont). The anode side of the membrane was made hydrophilic before the hot-pressing. Geometrical electrode area was 11.3 cm-2. 10 ml min-1 of 1 M (=mol dm-3) sulfuric acid, and 5 ml min-1 of 10 mol% TL / MCH were circulated to the anode and the cathode compartments, respectively. 10 mol% concentration of TL feed simulates at the vicinity of outlet in a practical electrolyzer. A Luggin capillary for a RHE was placed near the anode. Polarization was evaluated with constant cell voltage measurement for 5 min at 1.3-5.0 V and 60oC. During the constant cell voltage measurement, the volume of generated hydrogen was determined to evaluate the current efficiency. Resistance of electrolyte evaluated from high frequency intercept in AC impedance at 10-1~105Hz. Results and discussion Figure 1 shows the IR corrected polarization curves with 10 mol% TL feed with CPt (circular) that was loaded about 0.8 mg cm-2 of Pt and Cnon-Pt (triangle, diamond). Upper and lower vertical axes are anode and cathode potentials, respectively. Dashed dotted line shows the theoretical potential of 1.23 V and 0.15 V vs. RHE for anode and cathode reaction, respectively. The polarization curves of the anode with the CPt and Cnon-Pt were almost the same, while the potential of Cnon-Pt cathodes were lower than that of CPt cathode above 300 mA cm-2of current density region. The former showed diffusion limitation, while the latter did not show. Figure 2 shows the current efficiency (WTL →MCH) with 10 mol% concentration of TL feed at 60OC. Side bar shows the fluctuation of current density during constant cell voltage operation. At the low current density below 300 mA cm-2, the WTL →MCH of the CPt was significantly higher than that of the Cnon-Pt. The WTL →MCH of Cnon-Pt rapidly decreased when the current reached to 400 mA cm-2, which related to the large change of the cathode potential as shown in Figure 1. In all the current regions, the fluctuation of the CPt was significantly smaller than that of the Cnon-Pt. Therefore, the CPtwould promote the catalytic hydrogenation of TL with hydrogen bubble generated as side reaction in cathode. The decrease of hydrogen gas in the backing would lead to improve the TL mass transfer. Acknowledgments This work was supported by Cross-ministerial Strategic Innovation Promotion Program (SIP), “energy carrier” (Funding agency: JST). The Institute of Advanced Sciences (IAS) in Yokohama National University was supported by the MEXT Program for Promoting Reform of National Universities. We appreciate the person concerned them. References K. Ota, A. Ishihara, K. Matsuzawa, and S. Mitsushima, Electrochemistry, 78, 970 (2010). N. Itou, Hydrogen Energy Systems Society, 33, 9 (2008). S. Mitsushima, Y. Takakuwa, K. Nagasawa, K. Matsuzawa, Z. Awaludin, A. Kato, Y. Nishiki, Electrocatalysis, 7, 127 (2016). Figure 1
Introduction In order to reduce carbon dioxide emissions, a significant number of renewable energies that are uneven distribution with fluctuation must be introduced. Therefore, to increase renewable energies, energy carrier technology is needed for storage and transportation. Toluene-methylcyclohexane organic chemical hydride system is one of promising technologies as hydrogen storage and transportation. Electrohydrogenation of toluene with water splitting has higher theoretical energy conversion efficiency compare to a series process of water electrolysis and hydrogenation. Cathode side is a cathode membrane assembly with PtRu/C, which is applied PEFC technology. Anode is a dimensionally stable electrode for oxygen evolution reaction in acidic electrolyte using industrial electrolysis technology. In our previous study, we demonstrated good performance of the electrolyzer with hydrophilized membrane; however, hydrogen generated with low concentration of toluene feed, which should be improved (1). In this study, the effect of the design of toluene feed flow field on the cell voltage and the current efficiency has been investigated to increase conversion ratio from toluene to methylcyclohexane without hydrogen generation. Experimental A single cell electrolyzer made of titanium with 100 cm2of projected electrode area was used to determine the performance. Figure 1 shows the schematic drawing of flow field for the cathode. A parallel flow, which is usual for industrial electrolysis and liquid electrolyte fuel cells, a serpentine flow, which is conventional for polymer electrolyte fuel cells, and an interdigitated flow have been investigated to improve the performance of the electrolyzer. The anode flow field was parallel. A cathode was a carbon paper (35BC, SGL) coated 0.5 mgcm-2 of PtRu (TEC61E54, TKK) with Nafion dispersion. The cathode was pressed on a perfluoroethylene sulfuric acid (PFSA) membrane (Nafion® 117, DuPont) for a cathode membrane assembly. The membrane of the cathode side was mechanically hydrophilized. A DSE® anode with IrO2 based electrocatalyst is used for oxygen evolution. Backing of the anode was titanium felt. The anode was uniformlypressed on the membrane by elastic force of the titanium felt. 10 cm3 min-1 of toluene or 50% toluene-methylcyclohexane mixture and 1M (=moldm-3) of H2SO4were supplied to the cathode and anode for hydrogenation of toluene, respectively. Cell voltage was determined with 4 mVs-1 of voltage sweep from 1 V for toluene hydrogenation up to 0.5 A cm-2of the current density. Current efficiency was determined with constant cell voltage electrolysis with the volume measurement of gas evolution from cathode during the electrolysis.Internal resistance (iR) was determined with higher frequency intercept of AC impedance method. Results and discussion Figure 1 shows the cell voltage and the current efficiency as a function of the current density for electrohydrogenation of toluene at 60oC with various flow fields for the cathode. 100% of toluene or 50% toluene – methylcyclohexane mixture was fed to the cathode chamber. The internal resistances by AC impedance method were 0.25 Ω cm2 for all electrolyzers, which is almost same as the membrane area resistivity (2). The cell voltages for 50 and 100% toluene feed as a function of current density were almost the same for each flow design of the cathode. The cell voltage of parallel and interdigitated flow was 2.0 V at 0.4 Acm-2, and the cell voltage of the serpentine was a little larger than the other flow patterns. The current efficiency of hydrogenation decreased with the increase of current density, and the order from high current efficiency was the serpentine, interdigitated, and parallel flows. The difference among flow patterns was significantly for 100 % toluene feed, but it was very small for 50 % toluene feed. Turbulence flow would be better for mixing than laminar flow to feed toluene to the catalyst layer, and the order seems to be same to the flow velocity. Flow field design is important to increase toluene conversion. In addition, improvement of catalyst layer should also be important, because current efficiency of 50 % toluene feed seems to be controlled by mass transfer in the catalyst layer. Acknowledgment This work was supported by Council for Science, Technology and Innovation (CSTI), Cross-ministerial Strategic Innovation Promotion Program (SIP), “energy carrier” (Funding agency: JST). The Institute of Advanced Sciences (IAS) in YNU is supported by the MEXT Program for Promoting Reform of National Universities. We appreciate the person concerned them. References 1) S. Mitsushima, Y. Takakuwa, K. Nagasawa, Y. Sawaguchi, Y. Kohno, K. Matsuzawa, Z. Awaludin, A. Kato, Y. Nishiki, Electrocatalysis, 2016, 7, 238. 2) S. Slade, S. Campbell, T. Ralph, F. Walsh, J. Electrochem. Soc., 2002, 149, A1556. Figure 1
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.