Two-dimensional 1T-phase MnxIr1-xO2 for high-performance acidic oxygen evolution reaction.

Confined Ir single sites with triggered lattice oxygen redox: Toward boosted and sustained water oxidation catalysis

Membraneless Electrolyzers for Low-Cost Hydrogen Production in a Renewable Energy Future

The oxygen evolution reaction (OER) severely limits the efficiency of proton exchange membrane (PEM) electrolyzers due to slow reaction kinetics. IrO2 is currently a commonly used anode catalyst, but its large-scale application is limited due to its high price and scarce reserves. Herein, we reported a practical strategy to construct an acid OER catalyst where Iridium oxide loading and iridium element bulk doping are realized on the surface and inside of W18O49 nanowires by immersion adsorption, respectively. Specifically, W0.7Ir0.3Oy has an overpotential of 278 mV at 10 mA·cm-2 in 0.1 M HClO4. The mass activity of 714.10 A·gIr-1 at 1.53 V vs. the reversible hydrogen electrode (RHE) is 80 times that of IrO2, and it can run stably for 55 h. In the PEM water electrolyzer device, its mass activity reaches 3563.63 A·gIr-1 at the cell voltage of 2.0 V. This improved catalytic performance is attributed to the following aspects: (1) The electron transport between iridium and tungsten effectively improves the electronic structure of the catalyst; (2) the introduction of iridium into W18O49 by means of elemental bulk doping and nanoparticles supporting for the enhanced conductivity and electrochemically active surface area of the catalyst, resulting in extensive exposure of active sites and increased intrinsic activity; and (3) during the OER process, partial iridium elements in the bulk phase are precipitated, and iridium oxide is formed on the surface to maintain stable activity. This work provides a new idea for designing oxygen evolution catalysts with low iridium content for practical application in PEM electrolyzers.

Iridium oxide (IrO2) is one of the best known electrocatalysts for the oxygen evolution reaction (OER) taking place in strongly acidic solution. IrO2 nanocatalysts with high activity as well as long term catalytic stability, particularly at high current densities, are highly desirable for proton exchange membrane water electrolysis (PEM-WE). Here, we report a simple and cost-effective strategy for depositing ultrafine oxygen-defective IrOx nanoclusters (1 – 2 nm) on a high-surface-area, acid-stable titanium current collector (H-Ti@IrOx), through a repeated impregnation-annealing process. The high catalytically-active surface area resulting from the small size of IrOx and the preferable electronic structure originating from the presence of oxygen defects render H-Ti@IrOx outstanding OER performance, with low overpotentials of 277 and 336 mV to deliver 10 and 200 mA cm-2 in 0.5 M H2SO4. Moreover, H-Ti@IrOx also shows intrinsic specific activity of 0.04 mA cmcatalyst -2 and superior mass activity of 1500 A gIr -1 at an overpotential of 350 mV. Comprehensive experimental studies and density functional theory calculations confirm the important role of oxygen defects in the enhanced OER performance. Remarkably, H-Ti@IrOx can continuously catalyze the OER in 0.5 M H2SO4 at 200 mA cm-2 for 130 hours with minimal degradation, and with a higher IrOx loading it can sustain at such a high current density over 500 hours without significant performance decay, which holds substantial promise for use in PEM-WE.

Proton exchange membrane water electrolyzers (PEMWEs) have drawn attention among various hydrogen production technologies due to their zero-emission, high conversion efficiency, high hydrogen purity (>99.99%), and quick response under dynamic operation.1,2 With these auspicious characteristics in PEMWEs, they are believed to produce 40 % of green hydrogen by 2050 among all electrolyzer technologies. Nonetheless, many bottlenecks within PEMWEs still hinder their broader commercialization. Iridium oxide is the most widely used oxygen evolution reaction (OER) electrocatalyst at the anode. Moreover, this catalyst occupies the biggest portion (26–47%) of the overall cost of PEMWE systems, mostly due to the scarcity of iridium.3 Commercial iridium oxide catalysts are generally two types depending on the material structure: amorphous IrOx and crystalline IrO2. The trade-off relationship exists in catalytic activity vs. stability between amorphous and crystalline IrOx catalysts.4–6 To overcome these problems, fundamental studies of iridium oxide need to be conducted to reduce catalyst loading while maintaining high performance.Herein, we report the new iridium oxide catalysts (amorphous IrOx, crystalline IrO2, Ishifuku Metal) for the first time. These new iridium oxide catalysts are physically and electrochemically characterized. To be specific, we confirm the distinct characteristics of each catalyst using scanning electron microscopy (SEM), focused ion beam SEM (FIB-SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) analysis with nitrogen adsorption isotherm, Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). As a result, the crystalline IrO2 has a unique morphology with grown needles onto catalyst particles thereby the BET specific surface area of crystalline IrO2 (~110 m2 g-1) is over two times higher than amorphous IrOx (~50 m2 g-1). Electrochemical performance is evaluated for varied catalyst loadings of membrane electrode assembly (MEA). The catalyst loadings (0.10, 0.26, 0.35, and 0.85 mgIrOx cm-2) for both anode catalysts were prepared. The CV results of amorphous IrOx exhibit unique redox peaks under specific voltage (~0.8 and ~1.2 V vs. RHE), which indicates the transition of oxidation state. These peaks develop with CV cycling and become fully developed after 100 cycles, indicating that the surface of the catalyst takes some time to activate. On the other hand, crystalline IrO2 shows no specific redox peaks but rather has a double-layer capacitance under lower voltage (<0.5 V vs. RHE). Figure 1 shows 1.92 V (amorphous) and 1.94 V (crystalline) at 5 A cm-2 for 0.85 mg cm-2 loading, respectively. Both catalysts showed relatively low Tafel slopes of 43.8 mV dec-1 (amorphous IrOx) and 53.7 mV dec-1 (crystalline IrO2). This presentation will correlate the electrochemical performance described here to the structural properties of these two types of IrOx catalysts. Figure 1. Polarization curve for prepared iridium oxide catalysts (amorphous IrOx and crystalline IrO2). Both cells have anode loadings of 0.85 mg cm-2, cell temperature at 60 °C, 10 sccm for H2O flow rate at the anode, and dry for the cathode.

Commercialization of proton exchange membrane (PEM) electrolyzers for green hydrogen production have been recently achieved, but with a limited scale of low gigawatts (GW).1 Large-scale and sustainable deployment of PEM electrolyzers will face the challenges of scarcity and high cost of iridium (Ir) used in the anode to catalyze oxygen evolution reaction (OER). A 1 MW PEM electrolyzer stack currently uses ~0.4 kg of Ir based on an Ir loading of 1.5 mg/cm2, which contributes ~$60k cost per stack.2 Moreover, the Ir production has been about 8 tons/year in recent years.3 This can only support an annual production of 5 GW PEM electrolyzer if assuming 25% Ir is available for PEM electrolyzers with the same Ir loading. Therefore, lowering the Ir loading in PEM electrolyzers is urgently needed to meet the rapid expansion of the PEM electrolysis market.Several groups including Plug have developed supported Ir catalysts to lower the Ir loading by a factor of 5 without sacrifice in efficiency.4-8 However, all support used by far is non- or poorly electrically conductive. The conductivity of the electrodes relies solely on the surface IrOx, which sets stringent limits on the catalyst/electrode development, especially with low Ir contents. Here we first argue from fundamental aspects that the catalysts/electrodes with Ir on conductive support can be free of these limits. We further show that platinum (Pt) and titanium diboride (TiB2) powders are feasible candidates as conductive support for Ir-based OER catalysts. We demonstrated a TiB2 supported IrOx (IrOx/TiB2) catalyst synthesized via wet chemistry deposition without post heat treatment combines a mass activity towards OER with high conductivity. Its conductivity of ~30 S/cm2 is comparable to that of Vulcan carbon, and ~105 times that of the counterpart IrOx/W-TiO2 (W-TiO2 represents commercial tungsten doped TiO2 nanoparticles). Meanwhile, the IrOx/TiB2 catalyst shows a mass activity comparable to that of the counterpart IrOx/W-TiO2, twice that of commercial Ir black, and 50 times that of a commercial IrO2/TiO2 catalyst in acidic solution. Durability test showed that the Ir dissolution of the IrOx/TiB2 in acidic solution holding at 2 V for 100 hours is comparable to that of Ir black. Characterization of the IrOx/TiB2 showed small hydrous IrOx nanoparticles (1-2 nm) uniformly distributed on the surface of TiB2 nanoparticles (~58 nm) with an Ir content of ~33±7 wt%. Membrane electrode assembly evaluation on the IrOx/TiB2 catalyst is undergoing. The results will be reported and discussed. References (1) IEA, World Energy Outlook, 2022. https://iea.blob.core.windows.net/assets/830fe099-5530-48f2-a7c1-11f35d510983/WorldEnergyOutlook2022.pdf (accessed 2023-02-12).(2) Mittelsteadt, C. (Invited) Ir Strangelove: Or How I Learned to Stop Worrying and Embrace the PEM. ECS Meeting s 2022, MA2022-01, 1335-1335.(3) Seeking Alpha Home Page. https://seekingalpha.com/article/4399727-sibanye-should-benefit-from-hydrogen-wars-thanks-to-iridium-exposure (accessed 2023-02-12).(4) Böhm, D.; Beetz, M.; Gebauer, C.; Bernt, M.; Schröter, J.; Kornherr, M.; Zoller, F.; Bein, T.; Fattakhova-Rohlfing, D. Highly conductive titania supported iridium oxide nanoparticles with low overall iridium density as OER catalyst for large-scale PEM electrolysis. Applied Materials Today 2021, 24, 101134.(5) Pham, C. V.; Bühler, M.; Knöppel, J.; Bierling, M.; Seeberger, D.; Escalera-López, D.; Mayrhofer, K. J. J.; Cherevko, S.; Thiele, S. IrO2 coated TiO2 core-shell microparticles advance performance of low loading proton exchange membrane water electrolyzers. Appl. Catal. B‐Environ. 2020, 269, 118762.(6) Zhao, S.; Stocks, A.; Rasimick, B.; More, K.; Xu, H. Highly Active, Durable Dispersed Iridium Nanocatalysts for PEM Water Electrolyzers. J. Electrochem. Soc. 2018, 165, F82-F89.(7) Oakton, E.; Lebedev, D.; Povia, M.; Abbott, D. F.; Fabbri, E.; Fedorov, A.; Nachtegaal, M.; Copéret, C.; Schmidt, T. J. IrO2-TiO2: A high-surface-area, active, and stable electrocatalyst for the oxygen evolution reaction. ACS Catal. 2017, 7, 2346-2352.(8) Lewinski, K. A.; van der Vliet, D.; Luopa, S. M. NSTF advances for PEM electrolysis-the effect of alloying on activity of NSTF electrolyzer catalysts and performance of NSTF based PEM electrolyzers. ECS Trans 2015, 69, 893.

Hydrogen (H2) is a clean and efficient energy carrier with high gravimetric energy density, making it ideal for storing renewable energy. Proton-exchange membrane water electrolyzers (PEMWEs) are a promising technology for producing green hydrogen due to their high current density, compact design, and low operating temperature. However, the sluggish oxygen evolution reaction (OER) at the anode, which requires four-electron transfer in acidic media, remains a major bottleneck. While iridium oxide (IrO2) is the current benchmark OER catalyst, its high cost and scarcity limit widespread adoption. Ruthenium oxide (RuO2) has emerged as a promising alternative due to its superior OER activity and lower cost, but its poor stability under acidic conditions, caused by Ru leaching and over-oxidation, hinders practical applications.To address this, we developed RuO2 nanolayers epitaxially grown on rutile titanium dioxide (TiO2) nanofibers (NFs) as a highly efficient and stable acidic OER catalyst (NL-RuO2-250). The rutile TiO2 support was chosen for its excellent stability in acidic environments, moderate conductivity, and isostructural compatibility with RuO2, which minimizes interfacial energy and facilitates controlled catalyst growth. The one-dimensional TiO2 NF structure provides a high surface area and enhances electron transfer, while the RuO2 (101) crystal facet, predominantly exposed in NL-RuO2-250, offers optimized catalytic activity.The catalysts were synthesized through a hydrothermal process at varying pH conditions followed by heat treatment. At neutral pH (7), amorphous RuOx nanolayers formed on the TiO2 surface and were converted into crystalline nanolayers after heating at 250°C. In contrast, at higher pH (11.5), crystalline RuO2 nanosheets (NS-RuO2) formed with dominant exposure of the less active (110) facets. At acidic pH (2.5), weak interactions between Ru species and TiO2 resulted in sparsely distributed RuOx nanoparticles (NP-RuO2). XRD, TEM, and Raman analyses confirmed the epitaxial growth and strong interfacial interactions in NL-RuO2-250, which enhanced the stability and electronic properties of the catalyst.Electrochemical testing in a three-electrode system demonstrated that NL-RuO2-250 outperformed other catalysts. It required a low overpotential of 230 mV to achieve 10 mA cm-2 and a Tafel slope of 43 mV dec-1, indicating fast OER kinetics. NL-RuO2-250 also showed the highest electrochemical surface area (ECSA) and low charge transfer resistance, attributed to its nanolayer structure and optimized facet exposure. Stability tests revealed minimal performance degradation over 50 hours, with NL-RuO2-250 achieving a significantly higher stability number (S-number) compared to other catalysts, indicating reduced Ru leaching.Density functional theory (DFT) calculations revealed that the Ru (101) facets of NL-RuO2-250 facilitate the adsorbate evolution mechanism (AEM), which improves activity and stability by suppressing lattice oxygen participation. In situ Raman spectroscopy further confirmed that NL-RuO2-250 maintained stable Ru oxidation states during OER, avoiding over-oxidation and dissolution.When tested in a PEMWE single cell, NL-RuO2-250 achieved superior performance, requiring only 1.75 V to deliver 2 A cm-2. It also demonstrated excellent stability with negligible voltage drop over 24 hours at 0.2 A cm-2, outperforming commercial RuO2. This study highlights the importance of interfacial engineering and facet control in enhancing the performance and stability of Ru-based OER catalysts, offering a viable strategy for advancing PEMWE technology. Acknowledgement: This work is supported by the National Research Foundation of Korea (NRF) Grant funded by the Ministry of Education [NRF-00463589].

While lifetimes of up to 100,000 h have been reported for proton exchange membrane water electrolyzers (PEMWEs), the impact of dynamic operation on PEMWE lifetime requires further investigation [1]. Therefore, accelerated stress tests (ASTs) have been developed to assess degradation effects triggered by dynamic operation on a shorter time scale. Although voltage cycling can be easily employed to focus on catalyst degradation, many operation effects of a real system, such as gas crossover during idle periods, can only be simulated by such tests [2].Weiß et al. [3] developed an AST comprised of steps at high (3 A cm-2) and low (0.1 A cm-2) current densities, followed by an idle period at open circuit voltage (OCV) in order to mimic dynamic operation and shutdown of a PEMWE. When operating the cell at differential pressure (absolute pressures of 1 bar | 10 bar in anode/cathode compartment), H2 permeating through the membrane from the cathode into the anode compartment during the idle periods reduces the surface of the crystalline IrO2 catalyst (the most commonly used catalyst material for PEMWEs) to metallic Ir. Upon subsequent operation at high current densities and thus potentials, Ir is re-oxidized to an amorphous, hydrous iridium oxide. This amorphous oxide is known to exhibit a higher activity for the oxygen evolution reaction (OER), but a lower stability than crystalline IrO2 [4].This study aims to investigate the degradation of iridium oxide- and iridium metal-based anode catalyst layers during the above described OCV-AST developed by Weiß et al. [3]. A Pt-coated Ti-PTL is used to mitigate the buildup of contact resistances at the electrode/PTL interface [5]. IrO2/TiO2- and Ir/TiO2-based anode electrodes (with loadings of 1.7 – 1.9 mgIr cm-2) are coated onto a Nafion™ 212 membrane by using the decal transfer method, together with a Pt/C-based cathode (0.3 mgPt cm-2). These membrane electrode assemblies (MEAs) with the different anode catalysts are tested in 5 cm2 single-cells for approximately two weeks of intermittent operation. The Ir/TiO2 catalyst loses its metallic character in the two-week OCV-AST, as evidenced by the loss of hydrogen underpotential deposition features in the cyclic voltammogram (see region I in Fig. 1), which are well-defined at the beginning-of-test (BoT; blue line in Fig. 1) and smeared out at end-of-test (EoT, red line) [6]. Instead, features attributed to hydrous iridium oxide appear (see region II in Fig. 1), as this oxide is grown electrochemically at high potentials [4,6]. The evolution of this redox feature has been reported to also occur with the IrO2/TiO2 catalyst, indicating the transition of the less active crystalline to the amorphous iridium oxide with a higher OER activity [3].This study aims to deepen the understanding of change in the iridium oxidation state and in its OER activity during intermittent operation as well as its implications on voltage losses. We will further investigate the impact of different operating conditions on the degradation of the two different catalysts. A detailed electrochemical characterization will be supported by ex situ X-ray diffraction and -absorption spectroscopy measurements, further exploring the oxidation state of the catalyst materials.

On Sep. 25, 2023, Hydrogen energy ministerial meeting (H2 EM 2023) was held by the ministry of economy, trade and industry (METI) of Japanese government as online special event with cabinet members and officials from 23 countries, regions, and organizations. Participants shared the additional global goals to increase hydrogen demand which could potentially reach 150 million ton by 2030, with up to 90 million ton being demand for renewable and low-carbon hydrogen. In the chair’s summary of meeting, 0.7 Mt of H2 production with 700 MW of electrolyser installed as of 2022 [1-2].Proton exchange membrane water electrolysis (PEMWE) has already commercialized and recently applied its system for the Power-to-Gas (PtG) all over the world. In Kofu City in Yamanashi, Japan, the Komekurayama facilities has demonstrated the Power-to-Gas (P2G) system such as system of the intermittent generated electricity from the solar 10 MW generator and transform it to hydrogen using a PEMWE electrolyser of 1.5 MW capacity [3]. However, the cost of Ir metal as uses for material of anode has been raising in these two years, and it is almost 4 times higher than that of platinium in Japan [4-5]. From this point of view, the alternative anode with high durability should be required for the production of Green Hydrogen [6]. The catalytic activity of magnesium oxide has applied and studied in acidic solution [7-8] and we have also Mn oxide-based film fabricated by sputtering procedure for oxygen evolution reaction (OER) [9-10]. In this study, we have investigated the OER activity of Mn Oxide-based electrocatalysts as particle fabricated by thermal decomposition.MoO2 was prepared on Ti rods as a substrate. The 4 M Mn(NO3)26H2O aqueous solution was used as precursor. It dropped on substrate, and the thermal decomposition was demonstrated at 220 oC for 1 h. The loading amounts of MoO2 was constant at 1.1 mg cm-2. thickness of ZrO2 film was 10 nm for preparation. We used conventional three electrode cell with each sample as working electrode while the reversible hydrogen electrode (RHE) and carbon plate were used as reference and counter electrode to demonstrate the electrochemical measurement in 1 M H2SO4 solution with saturated nitrogen atmosphere at 303 K. Several samples were demonstrated pretreatment from 0.05 to 1.2 V vs. RHE before the measurement of OER. The slow scan voltammetry was performed from 1.2 to 2.0 V to evaluate the OER activity.Figure 1 shows polarization curves of OER on MoO2 on Ti substrate (MnO2(TD)/Ti). For the comparison, Mn-TaOx on Ti fabricated by sputtering procedure (Mn-TaOx(Sputter)/Ti) in our previous study [10] also shows in Fig. 1. The vertical axis was shown by the geometric current density (i geo). The i geo at 2.0 V of MnO2(TD)/Ti was ca. 200 mA cm-2 and it was so much larger than that of Mn-TaOx(Sputter)/Ti because the shape of MnO2(TD)/Ti as particle was different from that Mn-TaOx(Sputter)/Ti as thin film. The i geo of MnO2(TD)/Ti was also similar to that of MnO2(TD)/FTO [8]. Tafel plots of OER on MnO2(TD)/Ti was 115 mV dec-1 while that of Mn-TaOx(Sputter)/Ti was 62 mV dec-1.Acknowledgement: This work is partially supported by JFE 21st Century Foundation.Reference https://www.meti.go.jp/english/press/2023/0925_002.htmlhttps://www.meti.go.jp/press/2023/09/20230925002/20230925002-1.pdfhttps://centromariomolina.org/wp-content/uploads/2022/06/Green-Hydrogen-CMM.pdfhttps://furuyametal.jp/english/fmbi/chart/?language=enhttps://gold.tanaka.co.jp/commodity/souba/d-platinum.php K. Ota, A. Ishihara, K. Matsuzawa, and S. Mitsushima, Electrochemistry, 78, 970 (2010).A. Li, H. Ooka, N. Bonnet, T. Hayashi, Y. Sun, Q. Jiang, C. Li, H. Han, and R. Nakamura, Angew. Chem. Int. Ed., 58, 5054 (2019). A. Li, S. Kong, C. Guo, H. Ooka, K. Adachi, D. Hashizume, Q. Jiang, H. Han, J. Xiao and R. Nakamura, Nature Catal., 5, 109 (2022). K. Matsuzawa, S. Hirayama, Y. Kohara, A. Ishihara, ECS Trans., 104(8), 337 (2021).K. Matsuzawa, Y. Kohara, S. Hirayama, S. Yamada and A. Ishihara, ECS Trans., 109(9), 451 (2022). Figure 1

Hydrogen, as a clean energy carrier, is of great potential to be an alternative fuel in the future. Proton exchange membrane (PEM) water electrolysis is hailed as the most desired technology for high purity hydrogen production and self-consistent with volatility of renewable energies, has ignited much attention in the past decades based on the high current density, greater energy efficiency, small mass-volume characteristic, easy handling and maintenance. To date, substantial efforts have been devoted to the development of advanced electrocatalysts to improve electrolytic efficiency and reduce the cost of PEM electrolyser. In this review, we firstly compare the alkaline water electrolysis (AWE), solid oxide electrolysis (SOE), and PEM water electrolysis and highlight the advantages of PEM water electrolysis. Furthermore, we summarize the recent progress in PEM water electrolysis including hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) electrocatalysts in the acidic electrolyte. We also introduce other PEM cell components (including membrane electrode assembly, current collector, and bipolar plate). Finally, the current challenges and an outlook for the future development of PEM water electrolysis technology for application in future hydrogen production are provided.

Hydrogen is regarded as the most promising energy carrier. The pure hydrogen produced from electrochemical water splitting by using renewable energy is the most attractive and effective approach.[1] In comparison to alkaline water electrolysis, proton exchange membrane water electrolyzers (PEMWEs) could operate at higher current densities, lower ohmic loss, more compact system design, faster system response and more stable towards load-cycling and shutdowns. [2] The sluggish kinetics of oxygen evolution reaction (OER) at the anode of PEMWEs has restricted its practical applications. To date, iridium (Ir) metal and its oxide are usually selected as the state-of-the-art catalyst for OER due to their robust and long-term durability under the harsh acidic conditions. Nevertheless, Ir is an extremely scarce element, and its price has been doubled in the past few years. The development of low cost and highly effective electrocatalyst for OER in an acidic medium is urgently needed but remains a great challenge.In this work, we have prepared an ultra-thin RuO2 nanosheets by a simple molten salt method. High resolution STEM results show that the as-prepared RuO2 nanosheets is about 1-2 nm in thickness and hold a large number of defects, like Ru vacancy, grain boundary and amorphous. Toward OER, the as-prepared RuO2 nanosheets demonstrate an outstanding OER activity in acidic electrolyte, with an overpotential of only 199 mV for reach the current density of 10 mA cm-2 geo at a catalyst loading of 125 μg cm-2 geo. At the overpotential of 230 mV, the specific and mass activities of RuO2 nanosheets electrode is up to 0.89 mA cm-2 oxide and 0.516 A mg-1 Ru, which is 14.9 and 80.5 times higher than that of commercial RuO2 catalyst, respectively. Density functional theory (DFT) calculations (Figure 2e and 2f) indicated that the Ru vacancy defect on RuO2 surface could servers as the highly active site for remarkably weaken the binding energies of *O as compared to that of *OOH, which decrease the energy gap between ΔGO and ΔGOOH and thus dramatic enhanced OER performance. We also applied the catalysts in a homemade PEMWE device, at the applied cell voltage of 1.65 V, the current density of the RuO2 nanosheets catalyst cell reaches 0.93 A cm-2, which is almost 3 times larger than that of the cell with commercial RuO2 catalyst (0.31 A cm-2) at the same conditions, demonstrating that the RuO2 nanosheets possess great potential toward developing high performance PEMWEs.This work is under progress. Meanwhile, further characterizations, including XRD, XPS and more detailed morphology and electrochemical performance characterization of the RuO2 nanosheets catalyst will be presented at the meeting.The work described in this paper was financially supported by the Shenzhen Clean Energy Research Institute (No. CERI-KY-2019-003), Shenzhen Peacock Plan (KQTD2016022620054656), Shenzhen Key Laboratory project (ZDSYS201603311013489), The authors acknowledge the assistance of SUSTech Core Research Facilities.

Defective Ru-doped α-MnO2 nanorods enabling efficient hydrazine oxidation for energy-saving hydrogen production via proton exchange membranes at near-neutral pH

Facets engineering of high entropy alloy (HEA) nanocrystals might be achieved via shape-controlled synthesis, which is promising but remains challenging in designing Ir-based catalysts towards efficient and robust oxygen evolution reaction (OER) in acidic medium. Herein, icosahedra nanocrystals featured with PdCu core and IrPdCuFeNiCoMo shell were prepared by wet-chemical reduction in one-pot, ascribing to the initial formation PdCu core and subsequent deposition and diffusion of IrPdCuFeNiCoMo HEA shell. Sequential selective chemical etching of PdCu core results in IrPdCuFeNiCoMo HEA nanocages, delivering an overpotential of 235 mV at 10 mA cm-2, 51.0 mV dec-1, and 1624 A gIr -1 at 1.50 V vs reversible hydrogen electrode in a conventional three electrode cell. In a proton exchange membrane water electrolyzer, it delivers a low cell voltage of 1.65 and 1.77 V at a current density of 1.0 and 2.0 A cm-2, respectively, and maintains stable over 900 h at 500 mA cm-2. Theoretical calculations attribute the enhanced intrinsic activity to the broad distribution of the binding energy for OER intermediates on IrPdCuFeNiCoMo HEA, which breaks the linear scaling relationship and accelerates the OER process.

Controlled Growth Interface of Charge Transfer Salts of Nickel-7,7,8,8-Tetracyanoquinodimethane on Surface of Graphdiyne

Magnetically modified electrocatalysts for oxygen evolution reaction in proton exchange membrane (PEM) water electrolyzers