Stability In Acidic Electrolyte Research Articles

High‐Efficiency Iridium‐Yttrium Alloy Catalyst for Acidic Water Electrolysis

AbstractProton exchange membrane (PEM) water electrolysis holds great promise in revolutionizing clean energy production by enabling the efficient generation of hydrogen. Nevertheless, a formidable challenge persists in the realm of designing electrocatalysts that are both highly active and acid‐resistant during the oxygen evolution reaction (OER), thereby mitigating the substantial kinetic barrier. In this study, the facile synthesis of iridium‐yttrium (IrY) alloy nanocatalysts via a thermal shock method is introduced, which exhibits exceptional activity in the context of acidic water oxidation. Through the strategic incorporation of dispersed Y into the lattice of Ir metal, the IrY catalyst demonstrates a notably low overpotential of 255 mV at a current density of 10 mA cm−2 and showcases remarkable catalytic stability in acidic electrolytes, enduring for over 500 h with a high current density of 100 mA cm−2. Through a comprehensive set of in situ characterizations and analytical methods, the formation of a surface Ir‐based oxide layer, induced by deprotonation and electrochemical oxidation is unveiled, which is notably stabilized by the presence of Y dopants. This stabilization of the active site imparts enhanced resistance to over‐oxidation and dissolution, underpinning the exceptional stability of the catalyst. Theoretical calculations suggest that the incorporation of Y into the catalyst structure has a significant impact on enhancing the reactivity of the oxygen intermediate (O*) at adjacent Ir sites, thus lowering the overpotential and promoting OER activity. The alloying approach presents a straightforward method for achieving atomic‐level modifications in catalyst design and can pave the way for the development of more effective and economically viable OER catalysts and beyond.

Te-doped-WSe2/W as a stable monolith catalyst for ampere-level current density hydrogen evolution reaction.

The development of efficient electrocatalysts for the hydrogen evolution reaction (HER) holds immense importance in the context of large-scale hydrogen production from water. Nevertheless, the practical application of such catalysts still relies on precious platinum-based materials. There is a pressing need to design high-performing, non-precious metal electrocatalysts capable of generating hydrogen at substantial current levels. We report here a stable monolith catalyst of Te-doped-WSe2 directly supported by a highly conductive W mesh. This catalyst demonstrates outstanding electrocatalytic performance and stability in acidic electrolytes, especially under high current conditions, surpassing the capabilities of commercial 5% Pt/C catalysts. Specifically, at current densities of 10 and 1200 mA cm-2, it exhibits a minimal overpotential of 79 and 232 mV, along with a small Tafel slope of 55 mV dec-1, respectively. The remarkable catalytic activity of Te-WSe2 can be attributed to the exceptional electron transfer facilitated by the stable monolithic structure, as well as the abundant and efficient active sites in the material. In addition, density functional theory calculations further indicate that Te doping adjusts H atom adsorption on various positions of WSe2, making it closer to thermal neutrality compared to the original material. This study presents an innovative approach to develop cost-effective HER electrocatalysts that perform optimally under high current density conditions.

Unveiling favorable synergy of tubules-like NiMoSe2 with defect-rich borocarbonitride over graphene or MXene for efficient hydrogen evolution reaction electrocatalysis

Hydrogen generation through water splitting has emerged as a promising avenue for green hydrogen fuel production. In this study, we introduce a novel strategy for enhancing hydrogen evolution reaction (HER) activity by combining tubules-like NiMoSe2 with the 2D basal planes of MXene (Ti3C2Tx), borocarbonitride (BCN) and reduced graphene oxide (RGO). A facile one-step hydrothermal approach is employed to achieve the in-situ growth of NiMoSe2 nanotubules on the surfaces of 2D Ti3C2Tx and BCN materials. Characterization techniques confirm the successful integration of these components, highlighting the role of residual functional groups in facilitating nucleation and growth. This unique hybrid structure harnesses the conductive properties of the 2D materials, while providing abundant active sites on the NiMoSe2 nanotubules. Notably, the NiMoSe2/BCN composite outperformed other materials, achieving an overpotential of 215.0 mV to reach a current density of 10 mA cm−2 with a Tafel slope of 88.0 mV dec−1, accompanied by long term stability in acidic electrolyte. This enhanced electrocatalytic performance is attributed to the synergy between NiMoSe2 and BCN, where BCN's defect sites can also act as nucleophiles for H+ ions, promoting electron transfer reactions. Comparative analysis with other state-of-the-art catalysts underscores the competitive performance of the NiMoSe2/BCN nanocomposites towards HER.

Hollow TiO2 Supports for Enhanced Acidic Oxygen Evolution Activity

The usage of scarce and expensive iridium as a catalyst for the acidic oxygen evolution reaction (OER) represents a significant barrier to up-scaling the deployment of proton exchange membrane water electrolysers (PEM-WEs). Accordingly, strategies such as nanostructuring catalysts to increase the electrochemical surface area (e.g. nanoparticles, single-atom catalysts, nanoclusters) as well as investigating mixed metal alloys and oxides (e.g. perovskites, pyrochlores) have been developed with promising half-cell performances. One further approach that has recently gained attention is the deployment of catalyst-supports whereby a high surface area support is used to scaffold the dispersed iridium catalyst.1 Analogous to the selection of a catalyst, the catalyst support must withstand the highly corrosive and oxidising conditions of a PEM-WE anode. Thus, metal oxides such as titanium dioxide are commonly deployed as catalyst-supports for acidic OER. The catalyst-support moiety must also be sufficiently conductive when integrated into the PEM-WE catalyst layers. Otherwise, the cell voltages required to generate sufficient activity will render the device impractical. Accordingly, strategies such as doping, or the addition of conductive layers between the catalyst and support have been investigated.2 In this study we investigate a unique support morphology that affords promising OER activity and stability in acidic electrolyte with high iridium mass activities. Specifically, we deploy a hollow TiO2 catalyst support,3 coated with a Au/Pd interlayer to provide electrical conductivity. The OER activity and stability is initially screened in a rotating disk electrode (RDE) configuration as a function of thermal treatments (reducing vs oxidising) as well as with at various Au/Pd (1 – 5 wt%) and Ir loadings (35 – 50 wt%). Our highest performing catalyst have a mass activity of around 480 A/gIr at 1.60 V vs RHE. The catalysts are subsequently investigated in a membrane electrode assembly (MEA) and subject to 10k accelerated stress test stability measurements. To understand the role of the support morphology, Au/Pd interlayer and iridium loadings on electrochemical performance, we also characterise the synthesised catalysts by (scanning) transmission electron microscopy (STEM/TEM), X-ray diffraction (XRD), X-ray photoelectron microscopy (XPS) and electrical conductivity measurements. Collectively, we report the critical role of the Au/Pd interlayer to enable such high electrochemical performance. We also show that the hollow structure of the TiO2 support may be enhancing mass transport in the catalyst layers. References 1 A. S. Pushkarev, I. V Pushkareva and D. G. Bessarabov, Energy & Fuels, 2022, 36, 6631–6625.2 Y. N. Regmi, E. Tzanetopoulos, G. Zeng, X. Peng, D. I. Kushner, T. A. Kistler, L. A. King and N. Danilovic, ACS Catal., 2020, 10, 13125–13135.3 U. S. Jonnalagadda, X. Su and J. J. Kwan, Ultrason. Sonochem., 2021, 73, 105530.

Engineering Electronic Structure of Nitrogen‐Carbon Sites by sp3‐Hybridized Carbon and Incorporating Chlorine to Boost Oxygen Reduction Activity

AbstractDevelopment of efficient and easy‐to‐prepare low‐cost oxygen reaction electrocatalysts is essential for widespread application of rechargeable Zn‐air batteries (ZABs). Herein, we mixed NaCl and ZIF‐8 by simple physical milling and pyrolysis to obtain a metal‐free porous electrocatalyst doped with Cl (mf‐pClNC). The mf‐pClNC electrocatalyst exhibits a good oxygen reduction reaction (ORR) activity (E1/2=0.91 V vs. RHE) and high stability in alkaline electrolyte, exceeding most of the reported transition metal carbon‐based electrocatalysts and being comparable to commercial Pt/C electrocatalysts. Likewise, the mf‐pClNC electrocatalyst also shows state‐of‐the‐art ORR activity and stability in acidic electrolyte. From experimental and theoretical calculations, the better ORR activity is most likely originated from the fact that the introduced Cl promotes the increase of sp3‐hybridized carbon, while the sp3‐hybridized carbon and Cl together modify the electronic structure of the N‐adjacent carbons, as the active sites, while NaCl molten‐salt etching provides abundant paths for the transport of electrons/protons. Furthermore, the liquid rechargeable ZAB using the mf‐pClNC electrocatalyst as the cathode shows a fulfilling performance with a peak power density of 276.88 mW cm−2. Flexible quasi‐solid‐state rechargeable ZAB constructed with the mf‐pClNC electrocatalyst as the cathode exhibits an exciting performance both at low, high and room temperatures.

Engineering Electronic Structure of Nitrogen-Carbon Sites by sp3 -Hybridized Carbon and Incorporating Chlorine to Boost Oxygen Reduction Activity.

Development of efficient and easy-to-prepare low-cost oxygen reaction electrocatalysts is essential for widespread application of rechargeable Zn-air batteries (ZABs). Herein, we mixed NaCl and ZIF-8 by simple physical milling and pyrolysis to obtain a metal-free porous electrocatalyst doped with Cl (mf-pClNC). The mf-pClNC electrocatalyst exhibits a good oxygen reduction reaction (ORR) activity (E1/2 =0.91 V vs. RHE) and high stability in alkaline electrolyte, exceeding most of the reported transition metal carbon-based electrocatalysts and being comparable to commercial Pt/C electrocatalysts. Likewise, the mf-pClNC electrocatalyst also shows state-of-the-art ORR activity and stability in acidic electrolyte. From experimental and theoretical calculations, the better ORR activity is most likely originated from the fact that the introduced Cl promotes the increase of sp3 -hybridized carbon, while the sp3 -hybridized carbon and Cl together modify the electronic structure of the N-adjacent carbons, as the active sites, while NaCl molten-salt etching provides abundant paths for the transport of electrons/protons. Furthermore, the liquid rechargeable ZAB using the mf-pClNC electrocatalyst as the cathode shows a fulfilling performance with a peak power density of 276.88 mW cm-2 . Flexible quasi-solid-state rechargeable ZAB constructed with the mf-pClNC electrocatalyst as the cathode exhibits an exciting performance both at low, high and room temperatures.

Mo-Doped Mesoporous RuO2 Spheres as High-Performance Acidic Oxygen Evolution Reaction Electrocatalyst.

The development of highly active and acid-stable electrocatalysts for oxygen evolution reaction (OER) is of great significance for water electrolysis technology. Herein, a highly efficient molybdenum-doped mesoporous ruthenium dioxide sphere (Mo-RuO2 ) catalyst is fabricated by a facile impregnation and post-calcination method using mesoporous carbon spheres to template the mesostructure. The optimal Mo0.15 -RuO2 catalyst with Mo doping amount of 15mol.% exhibits a significantly low overpotential of 147mV at 10mAcm-2 , a small Tafel slope of 38mVdecade-1 , and enhanced electrochemical stability in acidic electrolyte, far superior to the commercial RuO2 catalyst. The experimental results and theoretical analysis reveal that the remarkable electrocatalytic performance can be attributed to the large surface area of the mesoporous spherical structure, the structural robustness of the interconnected mesoporous framework, and the change in the electronic structure of Ru active sites induced by Mo doping. These excellent advantages make Mo-doped mesoporous RuO2 spheres a promising catalyst for highly efficient electrocatalytic OER in acidic media.

Fe and Zn Addition Effects of Ti Oxide-Based Electrocatalyst on Catalytic Activity for Oxygen Reduction Reaction

The conventional catalyst of polymer electrolyte fuel cell (PEFC) is a platinum which is categorized as precious metal with very high-cost material, and its performance is limited in principal. From this point of view, the non-precious metal electrocatalyst should be required. We have focused and studied group 4 and 5 metal oxide-based electrocatalyst as non-platinum catalysts for the oxygen reduction reaction (ORR) because of low-cost, abundant reserves, and high stability in acidic electrolytes [1-2]. We found that titanium oxide prepared from TiOTPyzPz supported on multi-walled carbon nanotubes had superior ORR activity [3]. On the other hand, it was published as an international patent that the addition of other elements such as Fe and Ni is affected to enhance the ORR activity of Ti oxide-based electrocatalyst [4]. We have also applied for the TiOTPyzPz as a starting material with Fe, Ni, and Zn addition to enhance the ORR activity of Ti oxide-based electrocatalyst [5-6]. In this study, we have investigated the addition effects of Zn and Fe for Ti oxide-based electrocatalyst on the catalytic activity for the ORR.2,3-Dicyanopyrazine, urea, and Ti isopropoxide were dissolved in quinoline and refluxed to synthesize TiOTPyzPz. Iron acetate and zinc acetate were also added to dissolve in quinoline to obtain the Fe and Zn-added TiOTPyzPz as a starting material. These starting materials were mixed with carbon nanotube by ball-milling to prepare the precursors. These precursors were heat-treated under low oxygen partial pressure at 900 oC for 3 h to obtain the oxide-based electrocatalyst powder. The catalyst powder was dispersed into 1-propanol with Nafion solution to prepare a catalyst ink. The ink was dropped on a glassy carbon rod to use as a working electrode in electrochemical measurement.Electrochemical measurements were performed in 0.5 mol dm-3 H2SO4 at 30 oC with a conventional 3-electrode cell. A reversible hydrogen electrode (RHE) and a glassy carbon plate were used as used as a reference and counter electrode, respectively. Slow scan voltammetry (SSV) was performed at a scan rate of 5 mV s-1 from 0.2 V to 1.2 V vs. RHE under O2 and N2. The ORR current (i ORR) was determined by calculating the difference between the current under O2 and N2.Figure 1 shows the ORR polarization curves Fe and/or Zn addition to the Ti oxide-based electrocatalysts. The Fe and Zn added Ti oxide-based electrocatalyst (Fe,Zn-TiOx) was obviously the highest activity for the ORR, and it was higher ORR activity than Fe added Ti oxide-based electrocatalyst (Fe-TiOx), Zn added Ti oxide-based electrocatalyst (Zn-TiOx), and Ti oxide-based electrocatalyst (TiOx) without addition. It reveals that the addition of Fe and Zn was found to be effective for enhancing the ORR activity, and Fe addition was more effective than Zn addition for enhancing the ORR activity. XRD pattern of TiOx shows several peaks identified TiO2-Rutile and TiC0.3N0.7 while the XRD pattern of Fe-TiOx, Zn-TiOx, and Fe,Zn-TiOx also shows several peaks identified similar to TiOx. According to results from ICP analysis, the contain amount of Ti and Fe in Fe,Zn-TiOx was similar to preparation amount in precursor, but that of Zn showed below detection limit. From SEM images, Zn-TiOx and Fe,Zn-TiOx have more space in its powder than Fe-TiOx and TiOx. Based on above results, it is suggested that Zn addition affected to increased electrochemical surface area of TiOx, and Fe addition affected to form active site [7] in TiOx as similar case as Zr oxide-based electrocatalyst [8].Acknowledgement: The authors thank New Energy and Industrial Technology Development Organization (NEDO) and ENEOS Tonen General Research / Development Encouragement & Scholarship Foundation for financial support.Reference A. Ishihara, Y. Ohgi, K. Matsuzawa, S. Mitsushima, and K. Ota, Electrochim. Acta, 55, 8005 (2010).A. Ishihara, S. Tominaka, S. Mitsushima, H. Imai, H. Imai, O. Sugino, and K. Ota, Curr. Opin. Electrochem., 21 , 234 (2020).S. Tominaka, A. Ishihara, T. Nagai, and K. Ota, ACS Omega, 2, 5209 (2017).K. Takahashi, T. Imai, R. Monden, Y. Wakisaka, and S. Sato, Oxygen Reduction Catalyst, Process for Producing Same, and Polymer Electrolyte Membrane Fuel Cell, WO/2013/008501.K. Matsuzawa, M. Obata, Y. Takeuchi, Y. Ohgi, K. Ikegami, T. Nagai, R. Monden and A. Ishihara, ECS Trans., 108(7), 181 (2022).K. Matsuzawa, M. Obata, Y. Takeuchi, Y. Ohgi, K. Ikegami, T. Nagai, R. Monden and A. Ishihara, ECS Trans., 108(7), 189 (2022).J-H. Kim, A. Ishihara, S. Mitsushima, N. Kamiya, and K. Ota, Acta, 52, 2492 (2007).Y. Takeuchi, K. Watanabe, K. Matsuzawa, T. Nagai, K. Ikegami, R. Monden, and A. Ishihara, Chem. Lett., 51, 927 (2022). Figure 1

Iontronic and electrochemical investigations of 2D tellurene in aqueous electrolytes

AbstractThe remarkable successes of graphene have sparked increasing interest in elemental two‐dimensional (2D) materials, also referred to as Xenes. Due to their chemical simplicity and appealing physiochemical properties, Xenes have shown particular potential for numerous (opto) electronic, iontronic, and energy applications. Among them, layered α‐phase tellurene has demonstrated the most promise, thanks to the recent successes in the chemical synthesis of highly crystalline 2D tellurene. However, the general electronic and electrochemical properties of tellurene in electrolyte systems remain ambiguous, hindering their further development. In this work, we studied the electrostatic gating, electrocatalysis, and electrochemical stability of tellurene in electrolyte systems. Our results show that tellurene obtained from both hydrothermal and chemical vapor deposition methods, two mainstream synthetic approaches for Xenes, demonstrates thickness‐dependent ambipolar transport with high hole mobility and stability in both aqueous electrolytes and ionic liquids. More importantly, the electrochemical properties of tellurene are investigated via the emerging on‐chip electrochemistry. Pristine tellurene demonstrates hydrogen evolution reaction with low Tafel slopes and remarkable electrochemical stability in acidic electrolytes over a large potential window. Our study provides a comprehensive understanding of the iontronic and electrochemical properties of tellurene, paving the way for the broad adoption of Xenes in sensors, synaptic devices, and electrocatalysis.

Atomically Dispersed FeN2P2 Motif with High Activity and Stability for Oxygen Reduction Reaction Over the Entire pH Range

AbstractThe past decade has witnessed the great potential of Fe‐based single‐atom electrocatalysis in catalyzing oxygen reduction reaction (ORR). However, it remains a grand challenge to substantially improve their intrinsic activity and long‐term stability in acidic electrolytes. Herein, we report a facile chemical vapor deposition strategy, by which high‐density Fe atoms (3.97 wt%) are coordinated with square‐planar para‐positioned nitrogen and phosphorus atoms in a hierarchical carbon framework. The as‐crafted atomically dispersed Fe catalyst (denoted Fe‐SA/PNC) manifests an outstanding activity towards ORR over the entire pH range. Specifically, the half‐wave potential of 0.92 V, 0.83 V, and 0.86 V vs. reversible hydrogen electrode (RHE) are attained in alkaline, neutral, and acidic electrolytes, respectively, representing the high performance among reported catalysts to date. Furthermore, after 30,000 durability cycles, the Fe‐SA/PNC remains to be stable with no visible performance decay when tested in 0.1 M KOH and 0.5 M H2SO4, and only a minor negative shift of 40 mV detected in 0.1 M HClO4, significantly outperforming commercial Pt/C counterpart. The coordination motif of Fe‐SA/PNC is validated by density functional theory (DFT) calculations. This work provides atomic‐level insight into improving the activity and stability of non‐noble metal ORR catalysts, opening up an avenue to craft the desired single‐atom electrocatalysts.

Atomically Dispersed FeN2 P2 Motif with High Activity and Stability for Oxygen Reduction Reaction Over the Entire pH Range.

The past decade has witnessed the great potential of Fe-based single-atom electrocatalysis in catalyzing oxygen reduction reaction (ORR). However, it remains a grand challenge to substantially improve their intrinsic activity and long-term stability in acidic electrolytes. Herein, we report a facile chemical vapor deposition strategy, by which high-density Fe atoms (3.97 wt%) are coordinated with square-planar para-positioned nitrogen and phosphorus atoms in a hierarchical carbon framework. The as-crafted atomically dispersed Fe catalyst (denoted Fe-SA/PNC) manifests an outstanding activity towards ORR over the entire pH range. Specifically, the half-wave potential of 0.92 V, 0.83 V, and 0.86 V vs. reversible hydrogen electrode (RHE) are attained in alkaline, neutral, and acidic electrolytes, respectively, representing the high performance among reported catalysts to date. Furthermore, after 30,000 durability cycles, the Fe-SA/PNC remains to be stable with no visible performance decay when tested in 0.1 M KOH and 0.5 M H2 SO4 , and only a minor negative shift of 40 mV detected in 0.1 M HClO4 , significantly outperforming commercial Pt/C counterpart. The coordination motif of Fe-SA/PNC is validated by density functional theory (DFT) calculations. This work provides atomic-level insight into improving the activity and stability of non-noble metal ORR catalysts, opening up an avenue to craft the desired single-atom electrocatalysts.

Investigating the electrochemical performance of MnO2 polymorphs as cathode materials for aqueous proton batteries

Aqueous proton batteries (APBs) have attracted considerable attention due to the small size and fast kinetics of protons. However, the study of the cathode materials for APBs is unsatisfactory due to either low specific capacity or poor stability in acidic electrolytes, which greatly hinders the development of APBs. In this work, for the first time, six kinds of MnO2 polymorphs (α-, β-, δ-, γ-, λ-, and R-MnO2) are synthesized and systematically investigated to evaluate their potential as cathodes for APBs, among which the λ-MnO2 stands out by virtue of the 235 mAh g−1 specific capacity and 85% capacity retention rate over 500 cycles. To explain the reason for the stability of the λ-MnO2, DFT calculations are conducted, and the results indicate that the λ-MnO2 sustains minute volume expansion after proton insertion due to the slight Jahn-Teller distortion and robust all edge-sharing structure. The full battery performance shows the potential of the λ-MnO2 as a promising cathode for APBs with an excellent capacity of 202 mAh g−1 at 0.1 A g−1 and an outstanding retention rate of 80% after 1000 cycles. These results broaden the range of cathode materials and shed new light on the performance improvement of APBs.

Flexible and Binder‐Free Iron Phosphide Electrodes Using a Three‐Dimensional Support for High Hydrogen Productivity

AbstractIn this work, an inexpensive and reliable microstructured electrode for the hydrogen evolution reaction (HER) is developed. This cathode is made of Earth‐abundant elements consisting of iron phosphide as an electrocatalyst and carbon felt (CF) as a flexible conductive scaffold. Its porous character and binder‐free FeP coverage over the carbon fibers generate a high number of accessible active sites for the reaction, achieving a high value of the electrochemically active surface area. The electrode reaches 100 mA ⋅ cm−2 by applying only −53 mV vs RHE at 50 °C in 0.5 M H2SO4, demonstrating excellent electrocatalytic activity for the HER and outstanding stability in acidic electrolyte. Furthermore, the feasibility of these electrodes for industrial application is evaluated using a PEM electrolyzer. The developed prototype with a cathodic area of 1.8 cm2 shows a very promising performance, reaching 14.9 mmol H2 ⋅ h−1 ⋅ cm−2 (corresponding to 800 mA ⋅ cm−2) at a voltage of only 2.1 V.

A Pentagonal Defect-Rich Metal-Free Carbon Electrocatalyst for Boosting Acidic O2 Reduction to H2O2 Production

Metal-free carbon-based materials are considered one of the most promising two-electron oxygen reduction reaction (2e- ORR) electrocatalysts for the green synthesis of hydrogen peroxide (H2O2). However, most reported carbon electrocatalysts perform much more effectively in alkalis than in acids. Herein, by creatively using fullerene (C60) as the precursor subject to ammonia treatment, we designed and synthesized a pentagonal defect-rich nitrogen-doped carbon nanomaterial (PD/N-C). It achieves outstanding ORR activity, 2e- selectivity, and stability in acidic electrolytes, surpassing the benchmark PtHg4 alloy catalyst. Impressively, the flow cell based on the PD/N-C catalyst achieves nearly 100% Faraday efficiency with a remarkable H2O2 yield, representing the best improvement among all the metal-free catalysts. Experimental and theoretical results reveal that such superb 2e- ORR performance of PD/N-C originates from the synergism between pentagonal defects and nitrogen dopants. This work presents an effective strategy for the design and construction of highly efficient acid-resistant carbon electrocatalysts for H2O2 production and beyond.

Hybrid based on Phenazine Conjugated Microporous Polymer as a High‐Performance Organic Electrode in Aqueous Electrolytes

AbstractIncorporating redox active units in a 3D porous network is an encouraging strategy to enhance electrochemical performance of organic electrode materials. Herein, a new hybrid composed by phenazine‐based conjugated microporous polymer (IEP‐27‐SR, stand for IMDEA Energy Polymer number 27) and single‐walled carbon nanotubes (SWCNTs) and graphene oxide (RGO) is synthesized, fully characterized and tested electrochemically in different aqueous electrolyte conditions, i. e., at various pH values (1–12) and also with different charge carriers (H+ in acidic, and Li+, Na+, K+ in neutral and alkaline electrolytes). Although the IEP‐27‐SR is found to be very versatile showing very good electrochemistry both in alkaline and acidic solution, it exhibits best specific capacity, redox kinetics and cycle stability in acidic electrolyte. Then encouragingly, when IEP‐27‐SR is combined with an activated carbon (AC) counter electrode to construct a proof‐of‐the‐concept device, the IEP‐27‐SR//AC demonstrates high specific capacity (168 mAh g−1 at 2 C), impressive rate performance (96 mAh g−1 at 60 C) and ultra‐long cycle stability (76 % capacity retention over 28800 cycles at 10 C; 2690 h) in 1 M H2SO4.

Insulating High-Entropy Ruthenium Oxide as a Highly Efficient Oxygen-Evolving Electrocatalyst in Acid

Designing efficient and economical oxygen-evolving catalysts in acid media is of prime importance to develop proton exchange membrane water electrolysis for hydrogen production but still remains a great challenge. Herein, by codoping of nonprecious Cr, W, and Cu elements into the lattice of RuIr-mixed oxide, we construct a high-entropy rutile (Ru0.2Ir0.2Cr0.2W0.2Cu0.2)O2 as a superior catalyst for acidic water oxidation. This oxide exhibits a small overpotential of 220 mV at 10 mA cm–2geo with good stability in acidic electrolyte. Its mass activity reaches up to 1480.9 A g–1noble metal at 1.53 V versus RHE, surpassing most reported Ru-based catalysts. Our microstructural analysis reveals that the multielement doping inhibits the crystalline grains coarsening due to the lattice distortion and hence increases the active surface areas. More interestingly, electronic structure studies demonstrate that these dopants result in a metal–insulator transition, which weakens the Ru–O binding strength and enhances the intrinsic activity of the active sites.

Co-N decorated three-dimensional graphene as an efficient electrocatalyst for boosting hydrogen evolution reaction

Hydrogen evolution reaction (HER) is important for hydrogen generation. Due to the scarcity and high cost of noble metal-based electrocatalysts, it is eager to develop non-precious metal electrocatalysts. In this work, atomic cobalt decorated on N-doped three-dimensional graphene (Co SA/3D-NG) electrocatalyst has been synthesized. Due to the hierarchical porous structure of three-dimensional graphene by coupling effects between Co and N, the Co SA/3D-NG electrocatalyst exhibits an enhanced HER activity. The potential is -180 mV at -10 mA cm−2 and the Tafel slope is 102.53 mV dec−1. It also presents highly electro-catalytic stability in acidic electrolytes. The work reveals a facile pathway to synthesizing efficient HER electrocatalysts.

A Static Tin-Manganese Battery with 30000-Cycle Lifespan Based on Stabilized Mn3+/Mn2+ Redox Chemistry.

High-potential Mn3+/Mn2+ redox couple (>1.3 V vs SHE) in a static battery system is rarely reported due to the shuttle and disproportionation of Mn3+ in aqueous solutions. Herein, based on reversible stripping/plating of the Sn anode and stabilized Mn2+/Mn3+ redox couple in the cathode, an aqueous Sn-Mn full battery is established in acidic electrolytes. Sn anode exhibits high deposition efficiency, low polarization, and excellent stability in acidic electrolytes. With the help of H+ and a complexing agent, a reversible conversion between Mn2+ and Mn3+ ions takes place on the graphite surface. Pyrophosphate ligand is initially employed to form a protective layer through a complexation process with Sn4+ on the electrode surface, effectively preventing Mn3+ from disproportionation and hindering the uncontrollable diffusion of Mn3+ to electrolytes. Benefiting from the rational design, the full battery delivers satisfied electrochemical performance including a large capacity (0.45 mAh cm-2 at 5 mA cm-2), high discharge plateau voltage (>1.6 V), excellent rate capability (58% retention from 5 to 30 mA cm-2), and superior cycling stability (no decay after 30 000 cycles). The battery design strategy realizes a robustly stable Mn3+/Mn2+ redox reaction, which broadens research into ultrafast acidic battery systems.

Palladium nanoparticles confined in uncoordinated amine groups of metal-organic frameworks as efficient hydrogen evolution electrocatalysts.

Hydrogen obtained through the electrolysis of water is a potential solution to the growing demand of human society for energy. In addition, water electrolysis generates less environmental pollution than fossil energy sources. However, the preparation of highly active and low-cost electrocatalysts remains a key challenge. Here, we report a facile and inexpensive method to prepare palladium nanoparticles (Pd NPs) supported on aminated (-NH2) metal-organic frameworks (MOF). The obtained electrocatalyst (Pd@Uio-66-NH2) exhibits excellent electrocatalytic performance for the hydrogen evolution reaction (HER), featuring an ultralow overpotential (34 mV at 10 mA cm-2), small Tafel slope (41 mV dec-1), and superior stability in acid electrolyte. Systematic characterization demonstrated that -NH2 can effectively stabilize palladium acetate as the Lewis base. Meanwhile, the strong interaction between the lone pair electrons and the d-orbital ensures that the Pd atoms are uniformly distributed in the MOF material, inhibiting the agglomeration of metal NPs in the reaction. This strategy provides an avenue to prepare inexpensive and highly active catalysts for HER in acidic media.

(Digital Presentation) Effects of Foreign Elements Added Oxide-Based Electrocatalyst for Oxygen Reduction Reaction as Non-Precious Metel Cathodes

On Dec. 2020, new MIRAI of fuel cell vehicle (FCV) from Toyota started to sell in Japan. However, the price of new model is almost same as previous model. For wide commercialization of FCV, it should be required for more development. One of the barriers of innovative system for the FCV is conventional platinum-based electrocatalyst. The cost of Pt is very expensive due to its very poor resources. Moreover, the conventional Pt-based electrocatalyst cannot reach enough performance for next generation FCV that is proposed in new roadmap released from NEDO, Japan. From this point of view, the non-precious metal electrocatalyst should be required for the breakthrough against above issue. We have focused and studied group 4 and 5 metal oxide-based electrocatalyst as non-platinum catalysts for the oxygen reduction reaction (ORR) because of low-cost, abundant reserves, and high stability in acidic electrolytes [1-2]. We found that titanium oxide prepared from TiOTPyzPz supported on multi-walled carbon nanotubes had superior ORR activity [3]. On the other hand, it was published as an international patent that the addition of other elements such as Fe and Ni is affected to enhance the ORR activity of Ti oxide-based electrocatalyst [4]. In this study, we have investigated to apply for the TiOTPyzPz as a starting material with and without Fe, Ni, and Zn addition to enhance the ORR activity of Ti oxide-based electrocatalyst.2,3-Dicyanopyrazine, urea, and Ti isopropoxide were dissolved in quinoline and refluxed to synthesize TiOTPyzPz. Iron acetate, Nickel acetate, and Zinc acetate were also added to dissolve in quinoline to obtain the Fe, Ni, and Zn-added TiOTPyzPz as a starting material. The molar ratio of Ti:Fe:Ni:Zn was set to constant. These starting materials were mixed with carbon nanotube by ball-milling to prepare the precursors. These precursors were heat-treated under low oxygen partial pressure for 3 h to obtain titanium oxide-based catalysts. The catalyst powder was dispersed into 1-propanol with Nafion solution to prepare a catalyst ink. The ink was dropped on a glassy carbon rod, and dried for an hour to use as a working electrode in electrochemical measurement.Electrochemical measurements were performed in 0.5 mol dm-3 H2SO4 at 30 oC with a conventional 3-electrode cell. A reversible hydrogen electrode (RHE) and a glassy carbon plate were used as used as a reference and counter electrode, respectively. Slow scan voltammetry (SSV) was performed at a scan rate of 5 mV s-1 from 0.2 V to 1.2 V vs. RHE under O2 and N2. The ORR current (i ORR) was determined by calculating the difference between the current under O2 and N2.Figure 1 shows the effect of Fe, Ni, and Zn addition to TiOTPyzPz as a starting material on the ORR polarization curves of the titanium oxide-based catalysts. The vertical axis is based on catalyst weight. Ti oxid-based electrocatalyst prepared from Fe, Ni, and Zn addition to TiOTPyzPz (TiOx-Fe, Ni, Zn) resulted in the increase in the onset potential for the ORR and ORR current compared to that without addition (TiOx), revealing that the addition of Fe, Ni, and Zn was found to be effective in improving the ORR activity. XRD pattern of TiOx shows several peaks identified TiO2-Rutile, TiO2-Anatanse and TiO2-Brookite while the XRD pattern of TiOx-Fe, Ni, Zn also shows several peaks identified similar to TiOx. In the case of XRD pattern of TiOx-Fe, Ni, Zn, the peak identified compounds relating to additional elements such as Fe, Ni and Zn does not detect strongly. It is suggested that the addition of Fe, Ni and Zn to TiOTPyzPz conduce to the distortion of crystal phase of TiO2 [5] and it affected to suppress the crystal growth of Ti oxide-based electrocatalyst. These facts are possibly contributed to enhance the ORR activity of TiOx-Fe, Ni, Zn compared to that of TiOx.Acknowledgement: The authors thank New Energy and Industrial Technology Development Organization (NEDO) and ENEOS Tonen General Research / Development Encouragement & Scholarship Foundation for financial support.Reference[1] A. Ishihara, Y. Ohgi, K. Matsuzawa, S. Mitsushima, and K. Ota, Electrochim. Acta, 55, 8005 (2010).[2] A. Ishihara, S. Tominaka, S. Mitsushima, H. Imai, H. Imai, O. Sugino, and K. Ota, Curr. Opin. Electrochem., 21 , 234 (2020).[3] S. Tominaka, A. Ishihara, T. Nagai, and K. Ota, ACS Omega, 2, 5209 (2017).[4] K. Takahashi, T. Imai, R. Monden, Y. Wakisaka, and S. Sato, Oxygen Reduction Catalyst, Process for Producing Same, and Polymer Electrolyte Membrane Fuel Cell, WO/2013/008501.[5] Y. Yamamoto, S. Kasamatsu, and O. Sugino, J. Phys. Chem. C, 123, 19486 (2019). Figure 1