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Developing cheap and highly durable non-noble metal catalysts for water electrolysis to sustainably produce hydrogen as alternatives to platinum-based catalysts is essential. Herein, we report graphene-encapsulated NiMo alloys as acid-stable non-noble metal catalyst electrodes. The graphene-encapsulated NiMo cathode showed a highly stable performance in the potential cycling test (10,000 cycles) from 0 to 5.0 A cm−2 and 100 h of durability at a 2.2 V constant cell voltage. A balance between catalytic activity and corrosion in acidic environments was achieved by tuning the number of N-doped graphene layers. Through their application in a full-cell PEM-type water electrolyzer, we verify that noble metal catalysts can be replaced by non-noble metal catalysts. Such cheap acid-stable non-noble metal electrodes have promising practical applications in PEM-type water electrolysis.

In this study, we designed and developed a compact electrolyzer for the evaluation of components in proton exchange membrane (PEM) water electrolysis. First, this electrolyzer features a precise pressure-control system that controls the active electrode area and facilitates setting the desired clamping pressure. This mechanism makes it possible to optimize the electrolyzer performance. Second, it has two reference electrodes that are connected on the faces of the active electrode area of the anode and the cathode on the PEM. The polarizations at the anode and the cathode, the membrane resistivity, and the porous transport layer (PTL) overpotential were measured. The details of the design are described, and the electrochemical performance was measured. The optimized clamping pressure for this electrolyzer component was obtained as the specific value. A new measurement method was developed for estimating polarizations at the anode and the cathode, membrane resistance, and PTL overpotential using two reference electrodes.

For electrocatalysts of oxygen evolution reaction (OER), a new accelerated durability test (ADT) protocol is presented. The protocol is designed to closely mimic the fluctuations of renewable energies. The unit cycle of the current ADT protocol represents the “ON/OFF” operation mode. In the “ON” step, the electrolyzer operates under a DC current of 0.6 A cm−2. In the “OFF” step, the electrocatalyst is subjected to a constant potential that is clearly more cathodic than its OER onset potential (namely, 0.3, 0.5, and 0.7 V vs. RHE) for 10 or 60 s. The transition from the “ON” state to the “OFF” state occurs through a cathodic linear sweep voltammetry of a fast sweep rate to mimic the sudden changes in the renewable power. A NiCoOx/Ni-mesh electrode was used as a case study. The electrode showed remarkable durability under continuous operation (i = 0.6 A cm−2) for about 900 hours. However, it did suffer severe degradation after a certain number of ADT cycles, and the rate of degradation mainly depends on the potential value and the duration of the “OFF” step. Interestingly, the inclusion of the 10-sec open-circuit potential step after the “ON” step clearly mitigates the impact of energy fluctuations on the durability of OER electrocatalysts.

The behavior of bubbles on a rotating ring-disk electrode (RRDE) during water electrolysis has been investigated as fundamental study to evaluate gas evolution reaction electrode activity. The gas evolved on the surface of the electrode reduced the active surface area and increased the overpotential for electrolysis. We investigated how the shape of the electrode affects the bubble behavior and how to obtain an optimal non-blockage electrode surface using a Pt rotating ring disk electrode (RRDE). Standard deviation (SD) of the electrolysis currents was obtained. The value of the SD is corelated with the bubble detachment phenomenon. We found that the rotation induced flux field removes the generated bubble with decrease of the SD. So, a larger SD indicates the bubble accumulation on the electrode surface, and the surface stranding in the gas film. The ring electrode showed higher current with smaller SD than disk electrode at an overpotential for both oxygen and hydrogen evolution reaction. Therefore, a ring electrode is better than a disk electrode to evaluate gas evolution reaction. The optimum current measurement condition is using ring electrode under rotation speed higher than 2500 rpm, because dependence of current and the SD on rotating speed was small enough. Under this condition, HER at − 0.1 V, the ring electrode delivers − 260 mA cm−2, and the disk delivers − 160 mA cm−2. For OER at 2.2 V, the ring electrode delivers 195 mA cm−2, and the disk electrode delivers 130 mA cm−2. The ring electrode capture about 35% more current than disk, which might be loss by the effect of the bubble blockage. In order to get better current measurement in a gas evolution reaction, using ring electrode to remove the bubbles from the electrode surface in a high rotation speed is recommended.

Introduction Currently, the use of renewable energy is being promoted as an approach to decarbonization. However, renewable energy requires stable energy storage and supply because the amount of electricity is affected by time and climate. One of the solutions is use of hydrogen as an energy source. As the demand for hydrogen increases in the future, a large amount of hydrogen will be needed, and the storage and transportation of large amounts of hydrogen will also be necessary. However, the methods for storing and transporting large amounts of hydrogen have not yet been established, and this is one of the challenges in the current hydrogen utilization. One of the methods for storing and transporting large amounts of hydrogen is the organic hydride method. The organic hydride method is a method of storing and transporting hydrogen using hydrogenation and dehydrogenation of organic compounds. Among these, the use of toluene and methylcyclohexane (MCH) has attracted attention. The advantages of using toluene and MCH include the following: because toluene and MCH are liquids at normal temperature and pressure, they can be transported at about 1/500th the volume of direct hydrogen gas transport; toluene and MCH can be reused; hydrogenation and dehydrogenation are the only reactions, so no byproducts are generated; and they can be transported in the same way as petroleum. Hydrogen can be transported in the same way as petroleum. Therefore, it is expected to be used as a storage and transport medium for hydrogen. A toluene direct electro hydrogenation electrolyzer is available as a means of hydrogenating toluene. In the toluene direct electro hydrogenation electrolyzer, hydrogen and toluene are supplied to the electrolyzer, and electricity is applied to protonate the hydrogen and supply it to toluene to produce MCH. The advantages are that cost and time losses can be reduced because water electrolysis and toluene hydrogenation can be performed simultaneously, there is no heat loss in the reaction, and the theoretical decomposition voltage can be reduced compared to electrolysis of water and hydrogenation of toluene separately. However, during hydrogenation of toluene, a part of the water being electrolyzed is transferred to the toluene reaction surface, reducing the reaction efficiency to MCH. In addition, part of the protonated hydrogen becomes hydrogen bubbles, which inhibit the fuel supply and reduce the reaction area. Furthermore, the phenomena of water movement and hydrogen bubbles in toluene hydrogenation have not yet been studied. In this study , we aim to understand the generation of hydrogen bubbles by visualizing the phenomena in toluene hydrogenation using a toluene direct electro hydrogenation electrolyzer with an X-ray CT system, and to provide a guideline for future research on the suppression of hydrogen bubble generation and water movement. Fig. 1 shows a schematic diagram of the toluene direct electro- hydrogenation electrolyzer used in this experiment. The electrolyzer consists of a catalyst layer, a gas diffusion layer (GDL), and a separator, in that order. The electrolyzer is operated by supplying toluene to the anode side and hydrogen to the cathode side, and electricity is supplied. Visualization of the interface between the GDL and catalyst layer on the cathode side of the electrolyzer during operation using an X-ray CT system allows the phenomena on the reaction surface to be visualized. Figure 2 Visualization of the inside of the electrolyzer during operation. Fig. 2 (a) shows the electrolyzer filled with MCH and (b) shows the electrolyzer filled with toluene. The toluene electrolyzer generates fewer hydrogen bubbles, which confirms that the reaction is normal, and the correlation between the current density and the generation of hydrogen bubbles is examined. Figure 1

Introduction Energy transport and storage system should be considered with new energy source installation such as solar and wind power. There are some methods for it, and organic hydride methods are highly paid attention. In these methods, toluene-methylcyclohexane (MCH) conversion system is a good candidate as an energy transport and storage system with some reasons such as easy handling, affinity with Japanese current infrastructure, and so on. In the toluene-MCH conversion system, direct-toluene hydrogenation is especially paid attention since the system can be easier and exothermic heat loss reaction is less than other methods, so total efficiency of direct method gets higher than other methods. However, there are some problems on it, and the most serious problem is optimizing water management in cathode [1,2]. In cathode, toluene and MCH are flowing, and water appears in cathode porous transport layer (PTL) by being transported from anode then the water interrupts fuel supplies and the conversion rate from toluene to MCH gets lower. Therefore, water management should be optimized for higher performance of the system. However, there is no research which is focusing on water movement in this system as far as we know. Therefore, in this study, the original cell was investigated which had a visualization window on the cathode surface and allowed us to visualize the water movement during operating the system, and water movement was investigated. Fig. 1 shows the cell configuration and the actual picture from visualization window. As shown in Fig.1(a), the original cell was developed. In the left side, there is a visualization window with sapphire glass and the surface of the cathode PTL can be shot by hi-speed camera and so on. Fig.1(b) shows the example of visualization results. The cell was set with the gravity direction lower side and flow direction upper. The image shows us cathode PTL and toluene-MCH flow with water droplet and hydrogen bubble. As it can be seen in Fig.1(b), there are some droplets with several sizes. The 0.5 – 1.5 mm diameter droplets can be recognized as water droplet by seeing the movement with movie. By using this system, the effects of different anode supplies were discussed on water and hydrogen generation. Reference [1] K. Nagasawa et al., Electrochemistry, 339-344, 86 (2018) [2] K. Nagasawa et al., Electrocatalysis, 164-169, 8 (2017) Figure 1

To utilize renewable electricity with fluctuation and localization, large-scale energy storage and transportation technologies using hydrogen energy carrier have been expected. In order to improve hydrogen energy carrier synthesis, we have studied one-step electrolysis for toluene electrohydrogenation and water decomposition using proton exchange membrane (PEM) electrolysis. This process has 1.09 V of theoretical decomposition voltage for simultaneous water electrolysis and toluene hydrogenation. As shown in Figure 1, anode reaction produces oxygen and proton, and proton transports cathode electrocatalyst layer through the PEM with water molecular. Water inhibits toluene transportation to reaction side and hydrogen evolution occurs as side reaction. We have reported electrolyzers that has cathode side of PEFC’s MEA like structure using PtRu/C and anode side of industrial electrolyzer like structure using mesh shape of DSE® electrode for oxygen evolution reaction, and sulfuric acid solution feeds as anolyte that is not only reactant but also for water management. Water back diffusion from cathode to anode enhances with sulfuric acid concentration. In addition, current efficiency with mesh type anode was higher than that with sintered fiber sheet type anode. The mesh shape of electrode makes current distribution that affects mass transfer pass distribution to improve current efficiency, although sheet type anode is lower overpotential because of large surface area [1 – 3]. As practical system, water transportation from anode to cathode should be supressed without sulfuric acid utilization, and electrochemical surface- area of anode should extend to reduce overpotential. In this study, we have investigated wet gas water feed for PEM electrolysis to reduce water transfer to cathode, because water transfer would control by relative humidity of wet gas that feed to anode for oxygen evolution reaction. Here, PEM water electrolysis type anode catalyst layer with ionomer was employed to reduce anode overpotential and to maintain ionic conduction in catalyst layer. Figure 1 shows the schematic drawing of toluene direct hydrogenation electrolyzers with water splitting. Figure 1 (a) is our conventional electrolyzer of H2SO4 solution feed, and Figure 1 (b) is wet air feed in this study. The anode side for wet air feed had polymer electrolyte fuel cell type serpentine gas flow channel. Anode catalyst layer was 1.0 mg cm-2 of IrOx (TKK) with Nafion ionomer. The porous transport layer was platinum plated sintered titanium sheet. PEM was Nafion 117 (Du Point), cathode catalyst layer was 0.5 mg cm-2 of PtRu/C with Nafion ionomer supported on a porous flow field of a carbon paper that was loaded 0.02 mg cm-2 platinum for chemical reaction of toluene and hydrogen. 5 mL min-1 of toluene or 10% toluene – methylcyclohexane and 1.0 L min-1 of wet air fed to cathode and anode, respectively. Operation temperature was 80oC. After the 100 % RH feed electrolysis, there is no product except methylcyclohexane in the liquid phase and water transportation from anode to cathode reduced one twentieth from the conventional electrolyzer fed 1 M H2SO4 operation at 60oC. In this condition, IR free cell voltage of the wet gas fed electrolyzer was significantly smaller than that of the conventional one because of high surface area anode. Internal resistance of the wet gas feed determined by AC impedance method was about two times higher than that of the conventional, and current efficiency maintained in the low current density region. The internal resistance increased in the high current density region where the membrane and ionomer dry up with electro osmosis water. In this region, current efficiency also decreases. In summary, wet gas feed water electrolysis for electrohydrogenation of toluene using a PEM electrolyzer is an interesting technology that combines water electrolyzer with water purification system and manages water feed to reduce water transportation to cathode to maintain current efficiency of with accurate control of relative humidity and gas feed amount. Acknowledgement This study was based on results obtained from the Development of Fundamental Technology for Advancement of Water Electrolysis Hydrogen Production in Advancement of Hydrogen Technologies and Utilization Project (P14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO). References Nagasawa, K. Tanimoto, J. Koike, K. Ikegami, S. Mitsushima, J Power Sources, 439, 227070 (2019). Oi, K. Nagasawa, T. Takamura, Y. Misu, K. Matsuoka, S. Mitsushima, ECS Meeting Abstracts, MA2021-02, 1737 (2021). Mitsushima, Y. Sugita, J. Koike, Y. Kuroda, K. Matsuoka, Y. Sato, K. Nagasawa, ECS Meeting Abstracts, MA2020-02, 2494 (2020). Figure 1

Introduction Water electrolysis is expected a key device to introduce large-scale renewable electricity under management of power grid and electrification of non-electric sector. While alkaline water electrolysis (AWE) systems are well-developed large system, degradation under fluctuated operation with start and stop operation is significant issue to combine photovoltaic and/or wind turbine generation is significant issue. In this study, we have been investigated reverse current, which is leak current through manifold of bipolar alkaline water electrolyzers, and electrode potential behavior of stop operation, and proposed accelerated durability test (ADT) protocol for start and stop operation. Experimental and modeling Figure 1 shows configuration of 4-cells bipolar alkaline water electrolyzer that was consisted with end plates of EP(-) and EP(+), bipolar plates of BP1 to BP3, anodes, separators, and cathodes with principle of reverse current. The end and bipolar plates were made of nickel. Anodes and cathodes were commercially available oxygen and hydrogen electrocatalyst coated nickel mesh electrodes (De Nora Permelec Ltd) with 27.8 cm2 of projected area. Zirfon Perl UTP500 (Agfa) was used for separators. Manifolds were made of Teflon tubes and 15 mL/min of 7 M (= mol/dm3) was circulated for each anolyte and catholyte chambers during measurements. An anode and a cathode set on a bipolar plate. During operation anodes and cathodes are oxidized and reduces, respectively. After stop, the anode and the cathode on a bipolar plate connects both electronically and ionically, so oxidized anode and reduced cathode surface discharges to same potential. In this study, we measured electrode potential and reverse current after 1 h water electrolysis of 80oC at 0.6 A/cm2. The reverse current was measured ionic current through communicating tube with D. C. clamp meter (KEW2510, Kyoritsu). Reverse current behavior was analyzed with COMSOL Multiphysics version 5.5 based 2-dimensional model of stack and height direction using experimentally anode and cathode potentials as functions of discharge for anode and cathodes. Results and discussion Figure 2 shows cell performances in the stacks and a picture of the lab-scale zero-gap configuration electrolyzer. All cells in a stack showed almost the same performance. The cell voltage was 2 V at 400 mA/cm2 at 30oC and was 1.8 V at 500 mA/cm2 at 80oC. Therefore, we think all cells and parts work well. Figure 3 shows reverse currents and electrode potentials as a function of time after 1 h electrolysis under 600 mA/cm2 at 30 or 80 oC. Here, the dashed lines in Fig. 3-a) were simulated value and were almost same after 20 s. The measured reverse current increased around 20 s. At this moment, outlet manifolds filled with electrolyte to increase ionic conduction among the chambers, which was not considered in the simulation. After degassed of manifolds, the reverse current decreased with time with the largest reverse current for the BP2. The reverse current at 80oC was significantly larger than that at 30oC. This difference could be explained the dependence of ionic resistance of manifold on temperature. At same moment, anode and cathode potentials on the end plates were almost constant. The anode cathode potentials on the bipolar plates decreased and increased with time, respectively. Both anode and cathode showed significantly potential change region. The final potentials of all electrodes were around 0.9 V vs. RHE. The potential change regions of the electrodes on the BP2 were earlier than others. Here, the anode and cathode potentials as functions of discharge were almost same for the electrode on all bipolar plates. Therefore, the average discharge functions for anode and cathode were treated as characteristics of electrodes of this study. Using this function, reverse current as a function of time could be expressed accurately using the developed model. From this model, reverse current, and electrode potentials as a function of time would be expected with discharge function of each electrode and ionic resistance of manifold. Figure 4 shows that a start & stop operation simulated ADT protocol based on bipolar electrolyzer measurements. We propose the combination of constant current electrolysis, potential sweep, and chronoamperometry as the inset of illustration in Fig. 4, because constant current measurement is easier to get reproductivity in high current that need accurate iR correction for constant potential measurement and current control measurement never simulate stop operation. Acknowledgements This study was based on results obtained from the Development of Fundamental Technology for Advancement of Water Electrolysis Hydrogen Production in Advancement of Hydrogen Technologies and Utilization Project (P14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO). Figure 1

The anode mass transport loss is one of the issues to expand the practical application scope of proton exchange membrane water electrolyzers (PEMWEs). However, there are few reports concerning the oxygen transport inside and near the anode catalyst layer (CL). Although especially near the anode CL, there are two transport mechanisms: gaseous oxygen and dissolved oxygen, there are no reports, as far as we could find, that experimentally examined the existence of dissolved oxygen in PEMWE. Herein, the bubble growth behavior near the anode catalyst was observed using a high-speed camera, and the bubble radius change was investigated. The radii of the bubbles continued to increase after they left the anode catalyst layer surface, and the existence of dissolved oxygen and the formation of an oxygen supersaturated region were confirmed. The existence of dissolved oxygen is an important factor in the future evaluation of anode mass transport loss in PEMWE and a good revelation for the future development of the anode porous structure to reduce the anode mass transport loss.

The oxidation of a cathode catalyst surface is one of the major factors for cathode catalyst degradation under polymer electrolyte fuel cell (PEFC) operating conditions; however, the oxidation kinetics of Pt cathode catalysts in a membrane electrode assembly with O2 has not been investigated. We have investigated operando Pt LIII-edge time-resolved X-ray absorption fine structure analysis for the Pt oxidation processes on Pt/C and Pt3Co/C cathode catalysts controlled by transient PEFC voltage operation (0.4 V → 0.7–1.0 V) synchronized with the rapid exchange of cathode gas (N2 → 10% O2 in N2). We plotted Pt valence and the coordination numbers of Pt–Pt and Pt–O bonds every 20 ms, and the rate constants of the structural parameters for the Pt oxidation were successfully estimated. The structural kinetics of the Pt oxidation at the cathode suggested differences in the Pt oxidation kinetics between the Pt/C and Pt3Co/C cathode catalysts, showing the kinetic control of the Pt oxidation rate by the alloying wi...

In this study, we investigated the effect of the design of the cathode flow-field structure on the electrochemical performance of the electrolyzer for the toluene-methylcyclohexane electrocatalytic hydrogenation synthesis system. The patterns of the basic flow-fields; i.e. parallel, interdigit, serpentine and porous-carbon, were investigated based on linear sweep voltammetry (LSV), internal, and cathodic and anodic charge transfer resistances with impedance spectroscopy and current efficiency. The flow-field pattern affected the toluene mass transportation and H 2 gas generation as a side reaction. Based on the LSV curve, the porous-carbon did not affect the overvoltage for the decrease in the toluene concentration, and showed the lowest cell voltage in the all flow-fields. The cathodic charge transfer resistance by impedance analysis and the current efficiency of the porous-carbon showed the highest performance in the all flow-fields over a wide toluene concentration range.

The organic hydride of the toluene/methylcyclohexane (TL/MCH) system is one of the best energy carriers for renewable energies. In order to improve the energy conversion efficiency of the toluene hydrogenation process with water splitting, we have proposed the direct TL electrohydrogenation along with the water splitting process using an electrolyzer and have improved its performance. An analysis of the polarizations was essential for further improvement. In this study, the polarization properties of the anode (IrO2-based DSE®) and cathode (PtRu/C) were independently evaluated using a small electrolyzer equipped with a reversible hydrogen electrode (RHE). The cathode polarization was dominated by mass transfer above 100 mA cm−2. On the other hand, the anode polarization was dominated by a charge transfer process on the catalyst.

We have investigated the electrochemical hydrogenation of toluene using a PEM reactor for development of an organic chemical hydride system. Especially, the influence of catalyst materials such as Pt, Ru, and PtRu for a PEM reactor on the by-product formation and product selectivity in the hydrogenation of toluene was investigated.

International audience; The kinetics of the toluene (TL) electrohydrogenation on a carbon-supported platinum catalyst (Pt/C) have been investigated as a fundamental study of the cathode reaction in an electrolyzer with water decomposition. Since the TL electrohydrogenation on a Pt wire and Pt/C catalyst is a fast kinetic reaction with a low solubility, and slow mass transfer in an aqueous electrolyte, a potential step sequence was employed to determine its kinetic performance. Based on this method, a non-faradic current and faradic current could be identified and thereafter separated by a capacitance simulation. This experiment was performed in a TL-saturated sulfuric acid electrolyte to minimize the effect of the TL mass transfer. Based on the mass transfer-free TL electrohydrogenation experimental results, the exchange current densities of the TL electrohydrogenation on the Pt/C were 0.48, 0.49, 0.72, and 0.8mAcm(-2) at 25, 40, 50, and 60 degrees C, respectively. We found that the carbon support has a high impact towards the TL electrohydrogenation on the Pt-supported material. The carbon material works as a sponge by absorbing TL from the solution, and providing a large TL coverage for the Pt surface. Finally, a Tafel plot of the TL electrohydrogenation on the Pt/C catalyst was obtained and the kinetic performance was determined. The apparent active energy of the TL electrohydrogenation on the Pt/C was then calculated as 13.1kJmol(-1).

In order to develop an efficient and greener method for organic chemical hydride production in the energy carrier system, the electrocatalytic hydrogenation of toluene to methylcyclohexane was carried out using a proton exchange membrane (PEM) reactor, which generally applied a polymer electrolyte fuel cell and industrial electrolysis technologies. The electrochemical conversion proceeded in high current efficiencies (>90%) under sufficiently mild conditions with various metal-supported catalysts such as Pt/C, Rh/C, Ru/C, and PtRu/C. For example, methylcyclohexane was obtained in 94% current efficiency by the electrochemical hydrogenation of toluene with PtRu/C. Although the current efficiency of the hydrogenation with Pt/C, Rh/C, and Ru/C apparently decreased under high current density conditions due to the side reaction (hydrogen evolution), the hydrogenation with PtRu/C catalysts proceeded in excellent efficiencies even under high current density conditions.

The degradation of Pt electrocatalysts in membrane electrode assemblies (MEAs) of polymer electrolyte fuel cells under working conditions is a serious problem for their practical use. Here we report the kinetics and mechanism of redox reactions at the surfaces of Pt/C and Pt3Co/C cathode electrocatalysts during catalyst degradation processes by an accelerated durability test (ADT) studied by operando time-resolved X-ray absorption fine structure (XAFS) spectroscopy. Systematic analysis of a series of Pt LIII-edge time-resolved XAFS spectra measured every 100 ms at different degradation stages revealed changes in the kinetics of Pt redox reactions on Pt/C and Pt3Co/C cathode electrocatalysts. In the case of Pt/C, as the number of ADT cycles increased, structural changes for Pt redox reactions (charging, surface, and subsurface oxidation) became less sensitive because of the agglomeration of catalyst particles. It was found that their rate constants were almost constant independent of the agglomeration of t...

This account article treats with spatially non-uniform degradation events of Pt/C cathode catalysts in polymer electrolyte fuel cells involving the formation and dissolution of positively charged Pt ions and detachment of metallic Pt nanoparticles/clusters, which were visualized by the same-view nano XAFS and STEM-EDS imaging technique under humid N2 atmosphere.

The organic chemical hydride method using the toluene (TL)/methylcyclohexane (MCH) system is one of the prospective energy carrier technologies for hydrogen storage and transportation. The direct electrohydrogenation of toluene with water decomposition using electric power is a highly efficient energy conversion process for the MCH synthesis. In this process, an IrO2-based directionally stable electrode® (DSE®) for the oxygen evolution reaction (OER) is used as the anode because of its good electrocatalytic activity and durability. However, further improvement in the activity is needed for practical applications. In this study, the effect of Zr addition substituted for Ta in IrO2-Ta2O5/Ti, which is a typical OER anode, on the electrocatalytic activity has been investigated in sulfuric acid with TL contamination. The activity of both the IrO2-Ta2O5/Ti and the IrO2-Ta2O5-ZrO2/Ti was higher and less affected by TL contamination than the IrO2/Ti. The activity of the IrO2-Ta2O5-ZrO2/Ti increased with the Zr content. The Zr addition increased the real surface area along with the increase in the double layer capacitance; on the other hand, the increase in activity was more than that of the surface area. Therefore, the Zr additive would affect not only the real surface area increase, but also the electrocatalytic activity.

The dynamic structural and electronic transformations of Pt/C, Pd@Pt(1 ML)/C, Pd@Pt(2 ML)/C cathode catalysts in polymer electrolyte fuel cells (PEFCs) during the potential-step operating processes between 0.4 and 1.4 VRHE (potential vs RHE) were characterized by in-situ (operando) time-resolved Pt LIII-edge quick-XAFS at 100 ms time-resolution. Potential-dependent surface structures and oxidation states of Pt, Pd@Pt(1 ML) and Pd@Pt(2 ML) nanoparticles on carbon at 0.4 and 1.4 VRHE were also analyzed by in-situ Pt LIII-edge and Pd K-edge quick-XAFS. The Pt, Pd@Pt(1 ML) and Pd@Pt(2 ML) nanoparticle surfaces were restructured and disordered at 1.4 VRHE, which were induced by strong Pt-O bonds as well as alloying effects. The rate constants for the changes of Pt valence, CN(Pt-Pt), CN(Pt-Pd) and CN(Pt-O) (CN: coordination number) in the potential-step operating processes were also determined and discussed in relation to the origin of oxygen reduction reaction (ORR) activities of the Pt/C, Pd@Pt(1 ML)/C and Pd@Pt(2 ML)/C cathode catalysts.

The electrical energy can be provided from renewable energy source such as solar and wind, thus making the electrocatalytic hydrogenation process is expected one of important technology to reduce carbon dioxide emission in organic synthesis industry. The selective hydrogenation of alkynes to Z-alkenes is highly important for the construction of numerous valuable compounds, such as bioactive molecules, natural products, flavors, and industrial materials. Although a number of methods for the stereoselective synthesis of Z-alkenes have been developed so far, the Lindlar catalytic semihydrogeneation of alkynes is a long-standing synthetic transformation and still remains the favored system. Howeve To develop more environmentally benign and efficient semihydrogenation systems, we have demonstrated electrocatalytic hydrogenation of diphenylacetylene (DPA) in a proton exchange membrane (PEM) reactor. 1 In our system, the oxidation of water was employed as an anodic process (Figure 1 (a)). Especially, in this work, we have investigated systematically influences of catalyst materials such as Pt, Pd, and PtPd alloy for a PEM reactor on the product selectivity for Z-stilbene and partial current density for Z-stilbene formation in the hydrogenation of diphenylacetylene. As a result, PtPd alloy with a composition of Pt1Pd99 was found to be a most suitable catalyst material in order to achieve both high partial current density for Z-stilbene formation and high Z-stilbene selectivity (Figures 1 (b) and (c)). As shown in Figure 1 (b), it was also found that the partial current density for Z-stilbene is much improved by the addition of a small amount of Pt which has the high hydrogenation activity. Moreover, the synergy of Pt electrocatalysis for the formation of adsorbed hydrogen species (Had) (H+ + e− → Had) and Pd catalysis for hydrogenation of DPA (2Had + DPA → Z-stilbene) might be required in order to achieve the high stereoselective formation of Z-stilbene. Acknowledgement This work was support by JST CREST Grant No. JPMJCR18R1, Japan. The authors gratefully acknowledge for ISHIFUKU Metal Industry corporation the generous gift for cathode catalysts. References 1) A. Fukazawa, J. Minoshima, K. Tanaka, Y. Hashimoto, Y. Kobori, Y. Sato, M. Atobe, ACS Sustain. Chem. Eng. 2019, 7, 11050–11055. Figure 1

Proton exchange membrane water electrolysis (PEMWE) has attracted much attention because of its advantages such as the ability to downsize the equipment and produce high-purity hydrogen. For further improvement of the efficiency and durability of PEMWE, it is necessary to separate and examine polarizations. However, it is difficult to separate the anodic and cathodic polarizations by the AC impedance method. Also, it is difficult to separate resistance polarizations by using the reference poles with normal electrodes as shown in Figure 1 (a). Therefore, we are developing a device in which the electrode arrangement of both poles is deliberately shifted and a reference electrode is placed on each of the anode and cathode, as shown in Figure 1 (a) [1]. Since the phenomena in PEMWE are complicated due to the mutual influence of material/electric charge transport and reaction distribution, a multiphysical numerical analysis considering the potential distribution in the shifted electrode structure have been performed using COMSOL Multiphysics 5.4. Ohm's law was solved for the ionic charge transport in the electrolyte and the ionomer of the catalyst layer and also applied to the contact resistance between the electrode and the current collector. Butler-Volmer's equation was used for the activation overpotential at both poles. Figure 1(b) shows the electrolyte potential distribution when the electrode arrangement is shifted, and the potential distribution was completely changed from the (a). Figure 2 shows the relationship between the shift amount of electrode and the potential difference between both reference electrodes. The potential difference between both reference electrodes increases as the shift amount of electrode increases, and the rate of change of the potential difference decreases as the shift amount increases. Design and data processing based on these numerical results will lead to the development of devices that can perform more accurate separation of polarizations. Reference 1) S. Mitsushima, H. Kashiwagi, K.Nagasawa, and Y. Kuroda, ECS Meet. Abstr., MA2019-02, 1715 (2019). Figure 1

Introduction To utilize renewable electricity with fluctuation and localization, large-scale energy storage and transportation technologies using hydrogen energy carrier have been expected. In order to improve hydrogen energy carrier synthesis, we have studied one-step electrolysis for toluene electrohydrogenation and water decomposition, which has cathode side of PEFC’s MEA like structure using PtRu/C and anode side of industrial electrolyzer like structure using mesh shape of DSE® electrode for oxygen evolution reaction. This process has 1.09 V of theoretical decomposition voltage for simultaneous water electrolysis and toluene hydrogenation. We had optimized the electrolyzer with stacked anode of fine and conventional mesh to get high faraday efficiency and low cell voltage [1]. However, ultra fine anode, which decreased cell voltage a lot, based on sintered titanium fiber porous plate significantly decreased faraday efficiency. In this study, layered catalyst layer of dot shape and whole surface coating had been investigated to enhance mass transportation of toluene into the catalyst layer to improve faraday efficiency using ultra fine mesh anode, in order to develop efficient toluene direct hydrogenation electrolyzer with low cell voltage and high faraday efficiency. Experimental Figure 1 shows the schematic drawing dot shape cathode catalyst layer of square and diamond type that was consisted of 1.2 x 1.2 mm2 square dots with different direction. The dot shape was formed on a proton exchange membrane (Nafion®117, DuPont) and whole surface catalyst layer was formed on a carbon paper (35BC, SGL carbon ltd.) dispersed 0.5 mg cm-2 of Pt/C for chemical hydrogenation using by-product of hydrogen. The Pt-Ru/C (TEC61E54, TKK) loading was 0.75 mgcm-2 of metal for the layered potion of dot and whole surface coating. The type is indicated with the ratio of metal loading of dot and uniform layers on a dot as x:(10-x). The anode was ultra fine mesh and stacked anode of fine and conventional DSE® for oxygen evolution (De Nora Permelec, Ltd.), which was iridium oxide based electrocatalyst coated sintered titanium fiber plate. During electrolysis, cathode reactant of 10% toluene – methylcyclohexane or 100% toluene, and anolyte of 1 M (=moldm-3) H2SO4 was circulated at a 10 mL min-1 of flow rate, respectively at 60oC. Current efficiency was determined with the volume ratio of generated hydrogen gas and toluene-methylcyclohexane solution. Results and discussion Figure 2 shows the iR-free cell voltage, current efficiency and internal resistance as a function of current density for various electrolyzers. Internal resistances determined by EIS measurement were in the range from 0.4 to 0.5 Wcm2 in variation. The cell voltage of the conventional type with the double mesh anode was significantly higher than others, although current efficiency was higher than others. The uniform electrocatalyst layer electrolyzer with ultra fine mesh anode showed the lowest current efficiency in these. Here, only difference between these two cells were only anode structure, therefore anode structure would affect to mass transfer of toluene into cathode catalyst layer through current distribution corresponded to the anode shape. Patterned catalyst layers make current distribution by themselves, and their current efficiency were higher than that with uniform catalyst layer, so the effectiveness of the dot shape cathode catalyst layer was confirmed. The current efficiency of the diamond shape was higher than that of square shape, especially the current efficiency of 3:7 of the diamond shape was close to the fine mesh electrolyzer. From the comparison among square, diamond, and double layer catalyst, the current efficiency was affected not only current distribution by a shape of dot but also reactant flow distribution in cathode side flow field. Figure 3 shows current density and cathode potential as a function of the metal loading ratio of dot and uniform layers on a dot: r dot at a current hydrogenation current density of 90, 95, and 100%. The current density was the highest at 30% of the ratio with the lowest cathode potential. Therefor, the selectivity of hydrogenation should not be controlled by kinetics of charge transfer of the electrocatalyst, and strongly affected by mass transfer process of toluene in the catalyst layer. The optimized shape catalyst layer of this study was the stack of the dot layer and thinner whole surface layer of 3:7. Acknowledgement DSE® anodes for oxygen evolution were supplied from De Nora Permelec (DNJ). Authors appreciate to Dr. A. Kato and Dr. Y. Nishiki, DNJ for the distribution of the anodes. References 1. Nagasawa, K. Tanimoto, J. Koike, K. Ikegami, S. Mitsushima, J Power Sources, 439, 227070 (2019). Figure 1

Z-alkenes are versatile building blocks in organic synthesis and often found in pharmaceuticals, perfumes, and natural products. Although a number of methods for stereoselective synthesis of Z-alkene have been developed so far, the Lindlar semihydrogeneation of alkynes is a long-standing synthetic transformation and still remains a privileged system. However, it used toxic Pb additive and a large amount of quinolone, and has other limitations such as narrow substrate scope. Therefore, development of a powerful and reliable system for stereoselective semihydrogenation of alkyne to Z-alkene as alternative to the Lindlar catalytic system is still challenging target. Under these backgrounds, we have demonstrated electrocatalytic hydrogenation in a proton exchange membrane reactor so called PEM reactor to develop a powerful and reliable stereoselective semihydrogenation system. Especially, in this work, we have investigated systematically influences of catalyst materials such as Pt, Pd, and PtPd alloy for a PEM reactor on the product selectivity for Z-stilbene and partial current density for Z-stilbene formation in the hydrogenation of diphenylacetylene. As a result, PtPd alloy with a composition of 1(Pt):99(Pd) was found to be a most suitable catalyst material in order to achieve both high Z-stilbene selectivity and high partial current density for Z-stilbene formation (Figure 1). The authors gratefully acknowledge support by JST CREST Grant No. JPMJCR18R1, Japan. Ref. A. Fukazawa, J. Minoshima, K. Tanaka, Y. Hashimoto, Y. Kobori, Y. Sato, M. Atobe, ACS Sustain. Chem. Eng. 2019, 7, 11050-11055. Figure 1

Introduction Water electrolysis is expected a key energy conversion system to introduce large-scale renewable electricity under power grid management. Here, less expensive large system is needed. Alkaline water electrolysis (AWE) systems are well-developed large system to combine hydropower generation, but fluctuated operation with start and stop operation is not considered for conventional systems. Therefore, improvement of durability to combine photovoltaic and/or wind turbine generation is significant issue. In this study, we have been investigated reverse current behavior of bipolar alkaline water electrolyzers and proposes accelerated durability test (ADT) protocol. Theoretical and Experimental Figure 1 shows configuration of bipolar alkaline water electrolyzer, principle of reverse current. An equivalent circuit to analyze reverse current is also shown in the figure. During electrolysis, surface Ni of anode oxidizes to Ni(III) and that of cathode reduces to Ni(0). They electronically connect on a bipolar plate and ionically connect through manifold to distribute electrolyte. In the equivalent circuit, electrochemical potential difference between anode and cathode on a bipolar plate correspond to electromotive force of Uk(t). The R 1 and R 2 correspond ionic resistances of branch and communicating tubes, respectively. Relationship among these parameters can describe as eq. 1 in Fig. 1 based on the Kirchhoff's laws, so reverse current would be estimated. In this study, we measured electrode potential and reverse current after 1 h water electrolysis at 0.6 Acm-2 for 2 to 4 cells stack bipolar electrolyzer using commercially available industrial anode and cathode (De Nora Permelec Ltd). The reverse current was measured ionic current through communicating tube with D. C. clamp meter. As bipolar electrolyzer evaluation, we measured electrode potential and reverse current after 1 h water electrolysis at 0.6 Acm-2 for 2 to 4 cells stack bipolar electrolyzer using the commercially available anode and cathode. Effective electrode size was 27 cm2. The reverse current was measured ionic current through communicating tube with D. C. clamp meter (KEW2510, Kyoritsu). As start & stop operation simulated ADT protocol, we propose the combination of constant current electrolysis, potential sweep, and chronoamperometry as the inset of illustration in Fig. 4, because constant current measurement is easier to get reproductivity in high current that need accurate iR correction for constant potential measurement and current control measurement never simulate stop operation. Results and discussion Figure 2 shows the setup of lab-scale electrolyzer and cell performances in the stacks. All cells showed almost the same performance. Figure 3 shows reverse currents and electrode potentials as a function of time for 2 to 4 cells stack electrolyzer. The longer cell stack had lager reverse current at initial period of stop operation. As the potential difference between anode and cathode decreased, the reverse current decreased. The anode potential significantly decreased certain time, and that for longer cell stack was shorter. For the 4 cells stack, the time for the BP2 was shorter than that for the BP1 and BP3. Simultaneously, the I 2 was larger than the I 1 and I 3. These behaviors could be explained with eq. 1 in the Fig. 1 with the same electromotive force of the U(t=0)s for initial period and time function of U(t)s with same surface condition for all cells at the end of electrolysis. Remarkable point is that the cathode potential of BP2 was higher than the anode, which is impossible with discharge of BP2 itself. This opposite potential of the BP2 would be forced by electromotive force of the BP1 and BP3. Figure 4 shows the anode potential at 10 mAcm-2 (E @10mAcm-2) of oxygen evolution reaction (OER) current during the ADT protocol with various minimum potential: E min. The all anodes significantly degraded for around 3-days test protocol, although DN851 was developed as an active and durable anode for conventional OER electrode. The degradation increased with decreases of the E min. Above 0 V vs. RHE of the E min, The E @10mAcm-2 increased after ca. 800 cycles of introduction period and reached around 1.69 V vs. RHE after 1900 cycles, although it increased from initial period and the increase continued around 2000 cycles for -0.3 V vs. RHE of the E min. From these experimental results, the E min of between 0 to 0.3 V vs. RHE might be suitable for the ADT protocol because of rapid degradation with robustness to the E min. Acknowledgements This study was based on results obtained from the Development of Fundamental Technology for Advancement of Water Electrolysis Hydrogen Production in Advancement of Hydrogen Technologies and Utilization Project commissioned by the New Energy and Industrial Technology Development Organization (NEDO). Figure 1

Electric power can be generated from renewable energy sources such as solar and wind, making electrocatalytic hydrogenation an important technology to reduce carbon dioxide emissions in the organic synthesis industry. In the present work, the electrocatalytic semihydrogenation of diphenylacetylene was carried out in a proton exchange membrane (PEM) reactor with carbon-supported Pt, Pd, and Pt–Pd alloy cathode catalysts. Diphenylacetylene introduced into the PEM reactor at less negative potentials underwent electrocatalytic hydrogenation to provide cis-stilbene as a main stereoisomer, with excellent current efficiencies. Among the investigated catalysts, the Pt–Pd alloy with a composition of 1(Pt):99(Pd) was found to be the most suitable for achieving both high cis-stilbene selectivity and a high production rate (partial current density) for cis-stilbene.

The electrocatalytic hydrogenation of o-xylene in a proton-exchange membrane (PEM) reactor with various cathode catalysts was carried out as a study of a model reaction for hydrogen storage. o-Xylene introduced in a PEM reactor underwent electrocatalytic hydrogenation to provide cis-1,2-dimethylcyclohexane as the main stereoisomer with moderate to good current efficiencies. The reaction proceeded in accordance with the Langmuir–Hinshelwood mechanism.

Large-scale technology for energy storage and transportation is needed to increase renewable energies which unevenly distribute with fluctuations, such as wind and solar power. The organic hydride of the toluene/methylcyclohexane system is one of the best energy carriers. In order to improve the energy conversion efficiency of the hydrogenation of toluene using electric power, a membrane electrolyzer, which consists of a carbon-supported precious metal-coated porous carbon cathode, perfluorosulfonic acid (PFSA) membrane separator, and DSE® anode for the oxygen evolution reaction, has been designed and evaluated. The activity of the PtRu/C catalyst layer for the electrohydrogenation of toluene was higher than that of Pt/C. Hydrophilization of the anode side of the PFSA effectively discharged oxygen gas from the anode compartment. The electrohydrogenation of toluene without hydrogen evolution has been successfully up to a 450 mA cm−2 current density with 100 % toluene feed at ca. 2 V cell voltage. In order to evaluate the conversion ratio for the hydrogenation, the current efficiency as a function of the current density was evaluated at various concentrations of toluene. Significant hydrogen was generated above 100 mA cm−2 of current density for 10 times the stoichiometry of a 5 % toluene feed. During the electrolysis, by-products were hardly detected except for hydrogen. Although the improvement of the mass transport in the catalyst layer occurred, more than 95 % of the toluene conversion with a high energy efficiency should be feasible based on these experiments.

We have achieved significant improvements for the oxygen reduction reaction activity and durability with new SnO2-nanoislands/Pt3Co/C catalysts in 0.1 M HClO4, which were regulated by a strategic fabrication using a new selective electrochemical Sn deposition method. The nano-SnO2/Pt3Co/C catalysts with Pt/Sn = 4/1, 9/1, 11/1, and 15/1 were characterized by STEM-EDS, XRD, XRF, XPS, in situ XAFS, and electrochemical measurements to have a Pt3Co core/Pt skeleton-skin structure decorated with SnO2 nanoislands at the compressive Pt surface with the defects and dislocations. The high performances of nano-SnO2/Pt3Co/C originate from efficient electronic modification of the Pt skin surface (site 1) by both the Co of the Pt3Co core and surface nano-SnO2 and more from the unique property of the periphery sites of the SnO2 nanoislands at the compressive Pt skeleton-skin surface (more active site 2), which were much more active than expected from the d-band center values. The white line peak intensity of the nano-SnO2/Pt3Co/C revealed no hysteresis in the potential up-down operations between 0.4 and 1.0 V versus RHE, unlike the cases of Pt/C and Pt3Co/C, resulting in the high ORR performance. Here we report development of a new class of cathode catalysts with two different active sites for next-generation polymer electrolyte fuel cells.

Repeated anode gas exchange (AGEX) cycles and cathode gas exchange (CGEX) cycles were applied to MEAs with Pt3Co/C cathode catalysts to investigate the degradation processes and to compare with the case of Pt/C. The structural and electronic changes of the catalysts during the feed gas-exchange cycles were examined at the top position area of the MEAs by in-situ XAFS and at the top and bottom positions by STEM-EDS. The ORR performance decreased steadily by the AGEX cycles though STEM revealed neither large cracks nor voids nor detached particles in the top position area of the MEA by the AGEX cycles where the electrochemical surface area (ECSA) remained unchanged. On the other hand, neither ORR performance nor ECSA decreased by the CGEX cycles though the particle size only in the bottom position area increased a little after the CGEX treatment. In-situ time-resolved XAFS spectra at Pt LIII-edge showed a decrease of the XANES white line peak height in case of the AGEX, which is not due to particle growth.

We have made the first success in the same-view imagings of 2D nano-XAFS and TEM/STEM-EDS under a humid N2 atmosphere for Pt/C cathode catalyst layers in membrane electrode assemblies (MEAs) of polymer electrolyte fuel cells (PEFCs) with Nafion membrane to examine the degradation of Pt/C cathodes by anode gas exchange cycles (start-up/shut-down simulations of PEFC vehicles). The same-view imaging under the humid N2 atmosphere provided unprecedented spatial information on the distribution of Pt nanoparticles and oxidation states in the Pt/C cathode catalyst layer as well as Nafion ionomer-filled nanoholes of carbon support in the wet MEA, which evidence the origin of the formation of Pt oxidation species and isolated Pt nanoparticles in the nanohole areas of the cathode layer with different Pt/ionomer ratios, relevant to the degradation of PEFC catalysts.