Noritake (Japan)

The improvement of the activity and durability of Pt-based electrocatalysts for oxygen reduction reaction (ORR) is essential to realize the widespread uses of polymer electrolyte fuel cells (PEFCs). Our group has developed support-free connected Pt-alloy catalysts, which consist of nanonetwork by the connection of nanoparticles with high electrical conductivity, thus eliminating the need for carbon support. The connected Pt1–Fe1 and Pt3–Co1 catalysts with chemically ordered structures show an ORR specific activity about ten times higher than a commercial Pt/C catalyst. These catalysts with carbon-support-free and chemically ordered structures improve the durability against start/stop and load cycles.1–3 However, these connected catalysts are prepared by the annealing method using high temperature annealing to form partial fusion of nanoparticles, resulting in thicker nanonetwork and decreased electrochemical surface area (ECSA).This study reports a new one-pot synthesis method (Pt shell method) using a two-step polyol process at low temperature (80–100 °C) to form connected nanoparticles. As illustrated in Figure 1a, first, metal nanoparticles are formed on spherical silica template (metal NPs/SiO2) by polyol process, and then the Pt atomic shell is formed on metal NPs/SiO2 by controlled polyol process, resulting in a connected metal@Pt nanonetwork (connected metal@Pt NPs/SiO2). Finally, by removal of silica template using an alkaline treatment, a support-free, connected metal@Pt core-shell nanoparticle catalyst with a porous hollow capsule structure is obtained, as shown in Figure 1b–d. In this synthesis method, nanoparticles are connected by Pt shell layers, which allow the process to be conducted at low temperatures. Therefore, the connected Pd@Pt nanoparticle catalysts synthesized by the Pt shell method showed 3–4 times higher ECSA than those synthesized by the conventional annealing method. Furthermore, by controlling the thickness of the Pt shell layers on the surface, the connected Pd@Pt nanoparticle with ca. 3.5 Pt-atomic layers on the surface achieved higher ORR mass and specific activities. The developed catalyst also showed high durability against load cycle in 0.1 M HClO4 electrolyte solution at 60 °C. After 10,000 load cycles, the connected nanoparticle structure remained, showing the high durability of the nanonetwork connected by the Pt shell layers.In this way, this study has demonstrated a new Pt shell method and shown that a support-free connected nanoparticle catalyst is useful as a PEFC cathode catalyst. The Pt shell method can form stable connected structures with metal nanoparticles other than Pd, thus it is expected that further structural optimization, including other metal species, will lead to the realization of advanced ORR catalysts. Acknowledgement: This presentation is based on results obtained from a project, JPNP20003, commissioned by the New Energy and Industrial Technology Development Organization (NEDO), Japan.

Highly durable anion-exchange membranes and ionomers are essential for developing cost-effective green hydrogen generation. The anion-exchange membrane and ionomer must withstand chemical attacks by OH– ions as well as nonlinear mechanical stress caused by irregular bubble formation when the electrolyzer is coupled with intermittent power sources. Herein, we examined the durability of a trimethylammonium-modified poly(fluorene-alt-tetrafluorophenylene) (PFT-C10-TMA)-based membrane and ionomer under dynamic operation to evaluate its competency to couple with intermittent power sources. The durability of membrane–electrode assembly (MEA) prepared using these polymer membrane and ionomer was evaluated by performing 1000 start–stop voltage cycles in 1 M KOH solution at 80 °C while varying the applied cell voltage. The electrochemical performances of the MEA and electrodes were simultaneously evaluated using an electrolyzer with reference electrodes, and the chemical structure of the polymer was examined before and after the durability test using NMR techniques. The MEA based on a commercial Sustainion XB-7 ionomer and X37-50 RT anion-exchange membranes showed the catalyst leaching during start–stop cycles, resulting in reduced cell performance. On the other hand, the MEAs with the PFT-C10-TMA membrane and ionomer demonstrated promising high chemical and mechanical durability under dynamic start–stop operation, encouraging the development of electrolyzers that can function with intermittent renewable power sources.

The glucosinolate-myrosinase defense system (GMDS), characteristic of Brassicales, is involved in plant defense. Previous single-cell transcriptomic analyses have reported the expression profiles of multiple GMDS-related cell types (i.e. myrosinase-rich myrosin idioblasts and multiple types of potential glucosinolate synthetic cells as well as a candidate S-cell for glucosinolate accumulation). However, differences in plant stages and cell-type annotation methods have hindered comparisons among studies. Here, we used the single-cell transcriptome profiles of extended Arabidopsis leaves and verified the distribution of previously used markers to refine the expression profiles of GMDS-associated cell types. Moreover, we performed beta-glucuronidase promoter assays to confirm the histological expression patterns of newly obtained markers for GMDS-associated candidates. As a result, we found a set of new specific reporters for myrosin cells and potential glucosinolate-producing cells.

A major challenge in direct formate anion-exchange membrane fuel cells (DF-AEMFCs) is the low chemical durability of membrane–electrode assemblies (MEAs). Here, we developed MEAs that combined polyphenylene-based electrolytes and a carbon-free cathode catalyst layer (CL). The polyphenylene-based electrolytes with a three-dimensionally twisted spirobifluorene (SBF) backbone possess excellent chemical stability. The carbon-free catalyst formed by a nanonetwork of connected Pt–Fe nanoparticles showed four–five times higher specific activity for oxygen reduction reaction than a conventional Pt/C catalyst in an alkaline electrolyte solution. The carbon-free structure in the connected Pt–Fe catalyst enhanced the durability against potential cycling. The MEA using SBF-based electrolytes and a connected Pt–Fe catalyst achieved a high power density of 219 mW cm–2 for DF-AEMFCs through MEA testing under different conditions. Notably, the high performance was retained even after 150 h of operation at 0.2 A cm–2 and 80 °C. Detailed structural analysis of the catalyst and polyelectrolyte materials used in the MEA indicated minor chemical degradation after long-term DF-AEMFC operation. The anode and cathode CLs were not delaminated and the membrane/CL interfaces were bonded properly after the MEA stability test. The cathode catalyst retained the connected Pt–Fe nanonetwork and hollow capsule structures. A small amount of Fe leached out from the catalyst; however, a chemically ordered fct phase was maintained in the catalyst. Cryo-transmission electron microscopy observations showed a swollen SBF-based ionomer layer with a coating thickness of ∼50 nm on the catalyst surface, which remained unchanged after the stability test. This study successfully demonstrated that carbon-free connected nanoparticle catalysts are more advantageous than Pt/C for AEMFCs and that MEAs for DF-AEMFCs with both high performance and stability can be developed, providing design guidelines for the development of advanced MEAs.

Environmentally safe and efficient production of renewable fuels are of great demand to meet the current global energy crisis and global warming. As a fuel, hydrogen has been considered as the most suitable source of clean and sustainable energy, which indeed promote the importance of electrochemical water splitting [1-3]. Efficient and stable electrocatalyst for both hydrogen and oxygen evolution reactions are inevitable for the commercialization of water electrolyzer. Comparatively, the oxygen evolution reaction (OER) is more sluggish than the hydrogen evolution reaction (HER), which in turn affect the overall efficiency of the water electrolysis [4]. The non-noble metal oxides-based catalysts in alkaline solution have been shown promising OER activity [5] however, the high alkaline condition and high oxidation potential affects the stability of the metal oxides.Bimetallic oxide of NiFe system has been found as an efficient catalyst for OER [6]. Various methods were demonstrated for the synthesis of NiFe catalyst and studied their OER activity. In the present work, we made NiFe catalyst through electrochemical deposition method. We deposited NiFe over Ni foam and modified Ni foam through the constant potential method and voltammetric method. The OER activity and stability of these catalysts were measured in alkaline solution. Among the various catalysts synthesized, the NiFe deposited over modified Ni foam through constant potential method has shown better OER activity, attained 10 mA/cm2 at 1.45 V (vs RHE) but after electrolysis the potential increased to 1.47 V, indicating the poor catalytic stability. Whereas the NiFe catalyst prepared through the voltammetric method has attained 10 mA/cm2 at 1.46 V and remained unchanged after electrolysis, indicating better catalytic activity and stability (Figure 1). Figure 1. Linear sweep voltammogram measured before and after electrolysis in 1 M KOH of electrodeposited NiFe catalyst prepared through (a) constant potential method and (b) voltammetric method. Acknowledgement This presentation is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO) References. 1 N. T. Suen, S. F. Hung, Q. Quan, N. Zhang, Y. J. Xu and H. M. Chen, Chem. Soc. Rev. 46, 337–365 (2017).2 M. I. Jamesh and X. Sun, J. Power Sources. 400, 31–68 (2018).3 S. Jung, C. C. L. McCrory, I. M. Ferrer, J. C. Peters and T. F. Jaramillo, J. Mater. Chem. A. 4, 3068–3076 (2016).4 M. Tahir, L. Pan, F. Idrees, X. Zhang, L. Wang, J. J. Zou and Z. L. Wang, Nano Energy. 37, 136–157 (2017).5 F. Song, L. Bai, A. Moysiadou, S. Lee, C. Hu, L. Liardet and X. Hu, J. Am. Chem. Soc. 140, 7748–7759 (2018).6 M. Gong and H. Dai, Nano Res. 8, 23–39 (2014). Figure 1

Abstract Formate is the one legitimate carbon‐neutral fuel that has the capability of being considered an alternative to alcohol fuels amidst the growing demand for efficient fuel‐cell systems. In this manuscript, we demonstrate, for the first time, a class of binary Pd−Ni alloy nanoparticles over two different carbon supports showing exceptional enhancement of the formate oxidation reaction (FOR) performance in alkaline medium, compared to Pd/C. The synergistic effects of Pd and oxophilic Ni along with the electronic structure alteration of Pd induced through alloying resulted in an effective change in its catalytic ability, leading to a 5‐time enhancement in the overall current density along with a lower overpotential during formate oxidation compared to Pd/C. The more active Pd catalytic sites of the nanoalloy helped to yield mass activities as high as 4.5 A mg−1Pd and 7.8 A mg−1Pd during FOR. The structural and electrochemical analysis justifies the synergistic effects and alterations in the Pd lattice ensuing a superior enhancement of electrochemically active Pd sites.

In a long history of photovoltaic innovations, various architectures of crystalline silicon solar cells have been evolved to result in the highest conversion efficiency (η) of those days as described in Best Research Cell Efficiency by NREL. The cells are characterized by three parameters of the power max (Pmax), the saturation current (Jsc) and open-circuit voltage (Voc), but the fill-factor (FF) can be deduced from those three parameters. The 36 outstanding cells of those days are picked up from the published papers to be plotted on the η-FF and η-Jsc•Voc planes, in which all kinds of the architectures of the cells are included, for instance, PERC, PERL, PERT, HIT, IBC, TopCon, POLO, POLO-IBC, and Hetero-IBC(HJ-IBC). The plots of the η of those outstanding solar cells against their FF or Jsc•Voc clearly reveal a linear relation among them, even they have been independently evolved. The linear relation seems to have some effective meanings. The linear relation being assumable as a straight line, a 87% of FF on the line, which was predicted as the limit of FF by M. Reusch, can meet well with 29% to 30% in efficiency, which have been expected as the efficiency limit of crystalline silicon solar cells by W. Schockley and J. Queisser, and R. Swanson.

Solar cell performances at low light intensity are practically more important for power generation capacity in the entire life cycle. Previous studies have revealed that efficiency and maximum power of the solar cells with low shunt resistance become lower at the low light intensity. In contrast, our study has demonstrated the effects of paste or glass frit as paste constituents on shunts and recombination, as well as open-circuit voltage of solar cells with floating contact method. However, the effects of the glass frit in the paste on the low light performances of the cells have not been actually clear yet. For this reason, in this study, the effects of the glass frit itself on the low light performances of the cells are investigated. This is because even though the glass frit is an indispensable constituent for silver paste to electrically contact to the solar cells, the effects of the glass frit itself on cell performance have not been clear yet. In conclusion, the glass frit itself makes the solar cell performances lower at the low light intensity, especially open-circuit voltage and fill factor, by causing shunts and recombination, which means that the effects of paste constituents on shunts and recombination are important not only for solar cell performances at 1 sun, but also for the performances at low light intensity.

We describe a multi-diamond-wire saw for cutting monocrystalline silicon bricks into thin (120 µm) and thick (200 µm) wafers and label as fresh- and worn-wire sides. While almost no difference was found in the fracture stress of the thick (200 µm) wafers cut from either side, the thin (120 µm) wafers showed a lower fracture stress in those from the fresh-wire side compared to the worn-wire side. This is a remarkable result when wafers are sawn with conventional diamond wire. On the contrary, wafers sawn with improved diamond wire (100d-M6/12) showed a higher fracture stress compared to those cut with conventional diamond wire (100d-M8/16), for both the fresh- and worn-wire sides. Observing the subsurface areas of wafers by micro-Raman spectroscopy, we succeeded in quantifying the defective silicon fraction as the Raman crystallinity factor (Φc). We found that wafers having a higher fracture strength had a larger Φc.