Nanosheet Catalyst Research Articles

Performance and Durability of Carbon-Free Ionomer-Free PEFC Cathode Using Pt Nanosheet Catalyst

Polymer electrolyte fuel cells (PEFCs) have been attracting attention as highly efficient power sources and have been commercialized for use in residential power plants and automobiles. However, further widespread adoption requires the development of low-platinum catalysts. Additionally, for installation in heavy duty vehicles such as large trucks, high durability at high temperatures is necessary. Pt nanosheets (Pt(ns)), consisting of several atomic layers of Pt with a flat structure, possess high mass activity and durability due to the high specific surface area and low surface energy [1]. Conventional PEFC electrodes consisting of carbon-supported platinum (Pt/C) catalyst and ionomer suffer from degradation due to dissolution/redeposition, Ostwald ripening, and agglomeration of Pt, corrosion of the carbon support, and Pt poisoning by ionomer. Therefore, using unsupported Pt(ns) for an electrode that consists of neither carbon nor ionomer is expected to eliminate the degradation factors, resulting in a highly active and durable electrode. The purpose of this study is to develop highly active and durable electrodes by using Pt(ns) and eliminating degradation factors by making them carbon-free and ionomer-free.Polycrystalline Pt(ns) was synthesized by interlayer oxidation of graphene, as described elsewhere [2]. Catalyst ink was prepared, and cathode catalyst layers were created by dropping or spraying it onto carbon paper. A membrane-electrode assembly (MEA) was made by hot-pressing the cathode catalyst layer together with an anode made of Pt/C onto an electrolyte membrane. Power generation was conducted at 80˚C by supplying H2 to the anode and O2 or air to the cathode, each humidified under ambient pressure. Durability was evaluated by repeatedly applying cyclic potentials between 1.0 V and 1.5 V, supplying N2 to the anode and cathode, and examining changes in the cyclic voltammogram.The I-V curves of MEAs with ionomer-free carbon-free Pt(ns) cathodes fabricated using drop-coating and spray-coating methods and measured using air and oxygen as the cathode supply gases are shown in Fig. 1. As demonstrated in the figure, the activation overpotential at low current density was high, suggesting a low Pt utilization. The shape of the I-V curve of MEA using the spray method at high current density indicated that the concentration overpotential was suppressed under oxygen conditions but was high under air conditions. On the other hand, the concentration overpotential of the MEA using the drop method was high even under oxygen conditions. This may be attributed to the small spaces between the restacked nanosheets, which inhibited diffusion.A start-stop simulated potential cycle test was conducted for the MEA using ionomer-free carbon-free Pt(ns) cathode. The CV curves measured after a certain number of cycles are shown in Fig. 2. As shown in the figure, the change in the shape of the CV was small, and the ECSA remaining rate of the electrode was above 80% even after 8000 cycles, whereas that of the Pt/C cathode was less than 50% after 4000 cycles. This suggests that carbon-free ionomer-free Pt(ns) electrode has the potential as highly durable low Pt electrodes.AcknowledgementPart of this paper is based on results obtained from a project, JPNP20003, subsidized by the New Energy and Industrial Technology Development Organization (NEDO).

Controllable synthesis and super electrochemical stability of copper phosphide (Cu3P) nanosheets catalyst in nearly neutral electrolyte

The catalytic activity and stability of cost-effective and highly efficient bifunctional electrocatalysts are crucial for electrochemical water splitting. However, the use of strongly alkaline or acidic electrolytes, which are commonly employed, poses environmental concerns. Therefore, the development of efficient electrocatalysts that can operate stably in neutral or near-neutral electrolytes holds significant importance. In this study, a self-supporting Cu3P/NF electrode was fabricated using a two-step method, wherein metal phosphide Cu3P was grown on a nickel foam (NF) substrate. Notably, the Cu3P/NF electrode exhibits an unexpected enhancement in electrochemical activity and stability when operated in an electrolyte consisting of CuSO4 and Na2CO3. The hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) on the Cu3P/NF electrode require overpotentials of 131 mV and 230 mV, respectively, to achieve a current density of 10 mA cm−2 and 50 mA cm−2. Moreover, the stability of the Cu3P/NF electrode for HER and OER is improved by 90.22 % and 74.54 %, respectively, with the inclusion of CuSO4 in the Na2CO3 electrolyte. The improved catalytic performance and stability of Cu3P/NF electrode with the addition of CuSO4 can be attributed to the prevention of Cu + oxidation through Cu2+ and the formation of a local H+ adsorption electric field by the SO42− electron cloud. These factors contribute to the enhanced electrocatalytic activity and stability of Cu3P. This work expands the efficient utilization of electrocatalysts in near-neutral electrolytes, which is of great value for the widespread application of electrocatalysts and environmental protection.

Construction of Pd-doped RuO2 nanosheets for efficient and stable acidic water oxidation

RuO2 has been considered a potential alternative to commercial IrO2 for the oxygen evolution reaction (OER) due to its superior intrinsic activity. However, its inherent structure dissolution in acidic environments restricts its commercial applications. In this study, we report a novel Pd-doped ruthenium oxide (Pd–RuO2) nanosheet catalyst that exhibits improved activity and stability through a synergistic effect of Pd modulation of Ru electronic structure and the two-dimensional structure. The catalyst exhibits excellent performance, achieving an overpotential of only 204 mV at a current density of 10 mA cm−2. Impressively, after undergoing 8000 cycles of cyclic voltammetry testing, the overpotential merely decreased by 5 mV. The PEM electrolyzer with Pd0.08Ru0.92O2 as an anode catalyst survived an almost 130 h operation at 200 mA cm−2. To elucidate the underlying mechanisms responsible for the enhanced stability, we conducted an X-ray photoelectron spectroscopy (XPS) analysis, which reveals that the electron transfer from Pd to Ru effectively circumvents the over-oxidation of Ru, thus playing a crucial role in enhancing the catalyst's stability. Furthermore, density functional theory (DFT) calculations provide compelling evidence that the introduction of Pd into RuO2 effectively modulates electron correlations and facilitates the electron transfer from Pd to Ru, thereby preventing the over-oxidation of Ru. Additionally, the application of the two-dimensional structure effectively inhibited the aggregation and growth of nanoparticles, further bolstering the structural integrity of the catalyst.

Promoting the efficiency and selectivity of NO3--to-NH3 reduction on Cu-O-Ti active sites via preferential glycol oxidation with holes.

The combined reductive and oxidative reaction is the essence of a solar-driven photoredox system. Unfortunately, most of these efforts focus on the specific half-reactions, and the key roles of complete photoredox reactions have been overlooked. Taking the nitrate reduction reaction (NO3-RR) as a typical multiple-electrons involved process, the selective reduction of the NO3- into ammonia (NH3) synthesis with high efficiency is still a grand challenge. Herein, a rational oxidative half-reaction is tailored to achieve the selective conversion of NO3- to NH3 on Cu-O-Ti active sites. Through the coupled NO3-RR with glycol oxidation reaction system, a superior NH3 photosynthesis rate of 16.04 ± 0.40 mmol gcat-1 h-1 with NO3- conversion ratio of 100% and almost 100% of NH3 selectivity is reached on Cu-O-Ti bimetallic oxide cluster-anchored TiO2 nanosheets (CuOx@TNS) catalyst. A combination of comprehensive in situ characterizations and theoretical calculations reveals the molecular mechanism of the synergistic interaction between NO3-RR and glycol oxidation pair on CuOx@TNS. The introduction of glycol accelerates the h+ consumption for the formation of alkoxy (•R) radicals to avoid the production of •OH radicals. The construction of Cu-O-Ti sites facilitates the preferential oxidation of glycol with h+ and enhances the production of e- to participate in NO3-RR. The efficiency and selectivity of NO3--to-NH3 synthesis are thus highly promoted on Cu-O-Ti active sites with the accelerated glycol oxidative half-reaction. This work upgrades the conventional half photocatalysis into a complete photoredox system, demonstrating the tremendous potential for the precise regulation of reaction pathway and product selectivity.

Simultaneous electrosynthesis of nitrate and hydrogen by integrating ammonia oxidation and water reduction

Electrosynthesis of nitrate powered by renewable energy sources under mild conditions is an attractive alternative to the Oswald process for avoiding consuming large amounts of fossil fuels and eliminating associated greenhouse gas emissions. Here, we present an energy-saving and environmentally friendly strategy for efficient electrosynthesis of nitrate from ammonia oxidation by integrating hydrogen production from water reduction. We design a superior stable CuO nanosheet array catalyst and realize a total NOx– Faradaic efficiency of 98.7% via ammonia oxidation reaction (AOR) in an aqueous electrolyte. Hydrogen generation with a high Faradaic efficiency of 97.7% at the cathodic side is a concomitant AOR process. 0.2 mol L–1 NOx– can be produced after a long-term stability testing for 108 h, suggesting a potential practical application in decentralized nitrate and green hydrogen production.

Asymmetric Electrode Design for High-Area Capacity and High-Energy Efficiency Hybrid Zn Batteries.

Compared to Zn-air batteries, by integrating Zn-transition metal compound reactions and oxygen redox reactions at the cell level, hybrid Zn batteries are proposed to achieve higher energy density and energy efficiency. However, attaining relatively higher energy efficiency relies on controlling the discharge capacity. At high area capacities, the proportion of the high voltage section can be neglected, resulting in a lower energy efficiency similar to that of Zn-air batteries. Here, a high-loading integrated electrode with an asymmetric structure and asymmetric wettability is fabricated, which consists of a thick nickel hydroxide (Ni(OH)2) electrode layer with vertical array channels achieving high capacity and high utilization, and a thin NiCo2O4 nanopartical-decorated N-doped graphene nanosheets (NiCo2O4/N-G)catalyst layer with superior oxygen catalytic activity. The asymmetric wettability satisfies the wettability requirements for both Zn-Ni and Zn-air reactions. The hybrid Zn battery with the integrated electrode exhibits a remarkable peak power density of 141.9mWcm-2, superior rate performance with an energy efficiency of 71.4% even at 20mAcm-2, and exceptional cycling stability maintaining a stable energy efficiency of ≈84% at 2mAcm-2 over 100 cycles (400 h).

Nitrogen contained rhodium nanosheet catalysts for efficient hydrazine oxidation reaction

The hydrazine oxidation reaction (HzOR) has been considered as a more energy-efficient alternative to the oxygen evolution reaction in water electrolysis. To design efficient electrocatalysts for HzOR, precise engineering of materials is required to increase active sites and build electronic structures. Herein, nitrogen contained face-centered cubic rhodium (N-fcc-Rh) nanosheets are prepared by directly annealing metastable trigonal rhodium oxide precursor in the ammonia atmosphere. Benefiting from the abundant active sites and unique electronic structure, the optimal N-fcc-Rh-300 electrocatalyst achieves an ultra-low working potential of − 81 mV (vs. RHE) at 10 mA cm−2 in 1.0 M KOH/0.5 M N2H4. Density functional theory calculations suggest the N element in the N-fcc-Rh electrocatalyst enables to the reduction of the formation energy of the potential-determining step from *NH2NH2 to *NHNH2 for the HzOR process. This work reveals a new strategy to prepare advanced metal electrocatalysts for various electrochemical applications.

Outstanding low-temperature performance for NH3-SCR of NO over broad Cu-ZSM-5 sheet with highly exposed a-c orientation

Five ZSM-5-based catalysts with diverse zeolitic morphologies were prepared to experimentally investigate and computationally analyze the correlation between crystal plane and copper species. The types and numbers of copper species dispersed over Cu-ZSM-5 catalysts were emphatically determined to elucidate the structure-performance relationship of the Cu-ZSM-5 catalyst with broad sheet in the selective catalytic reduction (SCR) of NO by NH3. This study indicates that the broad Cu-ZSM-5 sheet exhibits outstanding low-temperature performance, achieving complete NOx removal at 250–550 °C. Operando X-ray absorption spectroscopy (XAS) experiments demonstrated this nanosheet catalyst has highly dispersed Cu2+ ions as key active sites, which are facilely solubilized by NH3 at low temperatures, further promoting rapid dynamic switching between Cu2+ and Cu+ species. And the density functional theory (DFT) calculations showed the Cu2+ forms a unique interaction with the [010] crystal plane, leading to a lower energy barrier of the rate-determining step, resulting in extraordinary NOx conversion.

Highly Stable Vertically Oriented 2H‐NbS2 Nanosheets on Carbon Nanotube Films toward Superior Electrocatalytic Activity

Abstract2D metallic transition‐metal dichalcogenides (MTMDCs) have attracted widespread research interest in the exploration of fundamental physical issues and energy‐related fields. Although relatively high catalytic activity has been predicted theoretically in the new type MTMDCs‐based electrocatalysts, their hydrogen evolution reaction (HER) performance is severely hampered by the insufficient catalytic stability due to structural degradation during long‐time use and limited active sites in planar electrode structures. Herein, the scalable synthesis of vertically‐oriented 2H‐NbS2 nanosheets is reported on low‐cost carbon nanotube (CNT) film substrates by a facile chemical vapor deposition route. The 3D vertically‐oriented 2H‐NbS2 nanosheets present abundant edge active sites and strong interface coupling with CNT thus possessing exceptional mechanical stability. These features impart the 3D nanosheets catalysts with remarkably low overpotentials of ≈55 mV at 10 mA cm−2 and ultra‐high exchange current density of ≈1445 µA cm−2, and negligible performance degradation after 200 h operation at the large current density, which are superior to those of other TMDCs‐based catalysts. This work hereby provides novel perspectives for the batch synthesis and application of 3D MTMDCs‐based electrocatalysts with greatly improved electrocatalytic performance and stability that are needed for practical applications.

Designing ultrastable Pt/CeO2-Al2O3 nanosheet catalysts for three-way catalysts applications

Designing Rh-free, especially Pt-only, three-way catalysts with improved low-temperature activity/stability is highly desirable. Herein, we demonstrate that ultrastable Pt/CeO2-Al2O3 nanosheet catalysts can be obtained based on a Sabatier principle of metal-support interaction. Tuning the surface coverage of penta-site rich γ-Al2O3 nanosheets (AlNS, weak adhesion to Pt) by CeO2 “nano-islands” (strong adhesion to Pt) can lead to the synthesis of Pt/60 wt.%CeO2-AlNS that have lower light-off temperatures for CO, hydrocarbons, and NO compared to conventional Pt/CeO2 and Pt/Al2O3 catalysts by 100–200 °C and a similar performance with the state-of-the-art Rh-based catalyst. Incorporating CeO2 on the surface of AlNS can retard the sintering of CeO2 during harsh redox hydrothermal aging, associate with the strong interaction between CeO2 “nano-island” and penta-site rich γ-Al2O3 nanosheets. Moreover, the improved activity/stability of Pt/CeO2-AlNS catalysts can be attributed to tuning of the Pt detachment and migration from and back to the CeO2 “nano-islands”, respectively, that keeps Pt as nanoclusters on CeO2, the most active species for three-way catalyst applications.

Triple reaction centers Vo-Ce-CuO nanosheets with single Ce atom for the Fenton-like degradation of niflumic acid

Vo (oxygen vacancy)-Ce-CuO nanosheet catalysts were studied for degrading niflumic acid (NFA) by the heterogeneous Fenton-like process (HFLP). NFA removal percentage of optimal Vo-Ce0.05-CuO reached 92% after 60 min of Fenton-like reactions and dropped only 0.28% after five times of recycles. Synergetic effects of triple reaction centers with electron-rich Vo centers, single Ce atom centers, and electron-deficient Cu centers have been demonstrated for generating hydroxyl radicals (OH) by H2O2 decomposition. The electrons from the organic pollutants adsorbed at the electron-deficient Cu centers could be transferred to Vo and Ce via the internal bridge bond to balance the electron transfer. H2O2 could directly obtain electrons from electron-rich Vo and single Ce atom centers to produce OH with a high H2O2 utilization efficiency instead of reducing metal ions by consuming H2O2. For the first time, we demonstrate that triple reaction centers with single Ce atom could improve the conversion percentage of H2O2 to OH with 71.1%. OH, HO2/O2− and 1O2 were the primary oxidants in the HFLP, in which OH played the dominant role.

N and P co-doped graphene-like carbon nanosheet as metal-free catalyst for selective oxidation of methacrolein to methacrylic acid: High methacrylic acid selectivity

Methacrylic acid (MAA) is an important chemical intermediate. In this study, a kind of nitrogen-phosphorus co-doped graphene-like carbon nanosheet catalysts have been prepared by co-pyrolysis of starch and (NH4)2HPO4, which have high specific surface area (1057.55 m2g−1) and excellent catalytic performance (35% of MAL conversion and 90% of MAA selectivity) for the selective oxidation of methacrolein to methacrylic acid. The graphite nitrogen provides new active sites for adsorption and activation of O2 which can accelerate the reaction. P in carbon skeleton can enrich the electron on the surface of carbon catalyst and turn the electrophilic groups to nucleophilic groups which can increase the MAA selectivity. This study provides a convenient and fast method to prepare efficient nitrogen and phosphorus co-doped carbon catalysts for the selective oxidation of methacrolein to methacrylic acid.

Ru Cluster Incorporated NiMoO(P)4 Nanosheet Arrays as High-Efficient Bifunctional Catalyst for Wind/Solar-To-Hydrogen Generation Systems.

Developing cost-efficient bifunctional water splitting catalysts is crucial for sustainable hydrogen energy applications. Herein, ruthenium (Ru)-incorporated and phosphorus (P)-doped nickel molybdate (Ru-NiMoO(P)4 ) nanosheet array catalysts are synthesized. Due to the synergy of Ru clusters and NiMoO(P)4 by the modulated electronic structure and the rich active sites, impressively, Ru-NiMoO(P)4 exhibits superior OER (194mV @ 50mA cm-2 ) and HER (24mV @ 10mA cm-2 ) activity in alkaline media, far exceeding that of commercial Pt/C and RuO2 catalysts. Meanwhile, as bifunctional catalyst, to drive the overall water splitting at the current density of 10mA cm-2 , Ru-NiMoO(P)4 requires only 1.45V and maintaining stable output for 100h. Furthermore, Ru-NiMoO(P)4 also possesses excellent capability for seawater electrolysis hydrogen production. Moreover, the successful demonstration of wind and solar hydrogen production systems provide the feasibility of the ultra-low Ru loading catalyst for large-scale hydrogen production in the future.

Tuning the Composition and Structure of Ni@MoC Nanosheets for Highly Active and Stable Electrocatalysis in Water Splitting

AbstractThe conventional electrolytic water‐splitting process for hydrogen production is plagued by high energy consumption, low efficiency, and the requirement of expensive catalysts. Therefore, finding effective, affordable, and stable catalysts to drive this reaction is urgently needed. We report a nanosheet catalyst composed of carbon nanotubes encapsulated with MoC/Mo2C, the Ni@MoC‐700 nanosheet showcases low overpotentials of 275 mV for the oxygen evolution reaction and 173 mV for the hydrogen evolution reaction at a current density of 10 mA ⋅ cm−2. Particularly noteworthy is its outstanding performance in a two‐electrode system, where a cell potential of merely 1.64 V is sufficient to achieve the desired current density of 10 mA ⋅ cm−2. Furthermore, the catalyst demonstrates exceptional durability, maintaining its activity over a continuous operation of 40 hours with only minimal attenuation in overpotential. These outstanding activity levels and long‐term stability unequivocally highlight the promising potential of the Ni@MoC‐700 catalyst for large‐scale water‐splitting applications.

Boosting electrocatalytic hydrazine oxidation at single-crystalline Ni nanosheets with embedded NiZn

Hydrazine oxidation reaction (HzOR) plays a crucial role in direct hydrazine fuel cells and holds promise for replacing the kinetics-sluggish oxygen evolution reaction in splitting water. While Ni–Zn alloys exhibit exceptional activity for HzOR, their synthesis under mild conditions remains a challenge. Herein, a Ni–Zn nanosheet catalyst with NiZn inclusion was prepared on Ni foam by controllable chemical etching together with ethylene glycol reduction. X-ray diffraction and transmission electron microscopy confirmed the single-crystalline nature and the presence of intermetallic NiZn. The strong interaction between Ni and ZnO, along with defects, facilitated the formation of this intermetallic compound. The Ni–Zn/Ni foam exhibits remarkable catalytic activity (214.3 ​mA ​cm−2 at 0.1 ​V) and durability (87.8 ​% retention after 24 ​h) towards hydrazine electrooxidation, thanks to the combined benefits of intermetallic NiZn, mesoporous nanosheets, microscopic defects, single-crystalline characteristics, and a coherent Ni–NiZn interface. This study provides a new method for designing highly active Ni–Zn electrocatalysts for HzOR.

Deep Reconstruction of the NiFeSP Nanosheet Catalyst for Large Current-Density Water Oxidation.

Evidence shows that the crucial factor in achieving efficient water electrolysis for hydrogen production is the design and synthesis of electrocatalysts that exhibit both high performance and cost-effectiveness for the oxygen evolution reaction (OER). Herein, the NiFeSP nanosheets were facilely prepared on a Ni foam (NF) substrate through a cost-effective electrodeposition method. The electrode structure composed of nanosheets offers a high density of active sites and superior electrical conductivity, thereby enhancing the efficiency of the OER. In addition, the NiFeSP/NF-600 nanosheets exhibit superhydrophilic and superaerophobic characteristics, which effectively enhance the mass-transfer process by facilitating the penetration of electrolytes and enabling rapid release of gas bubbles. Consequently, NiFeSP/NF-600 demonstrates superior electrocatalytic efficacy for OER, exhibiting an overpotential of 292 mV at a high current density of 500 mA cm-2 as well as an exceptional long-term durability of 100 h. More importantly, the rapid reconstruction of FeOOH and NiOOH species from NiFeSP/NF-600 may be the true active species for OER, which is revealed utilizing in situ Raman spectroscopy in conjunction with ex situ characterization. This study not only offers an ideal "pre-catalyst" for an extremely effective OER but also offers a thorough understanding of the mechanism underlying the structural evolution of electrocatalysts and the identification of their actual active sites.

PbHPO4 derived Pb catalysts modified by polyethylene glycol toward efficient CO2 electroreduction to formate

Surface ligands of catalytic materials can create a favorable reaction microenvironment which stabilizes reaction intermediates and enriches solvated reactants. Herein, a polyethylene glycol-modified Pb nanosheet (Pb-PEG) catalyst is developed through in situ electrochemical reconstruction of PEG-modified PbHPO4, for efficient CO2 electroreduction. Formate is selectively produced with a Faradaic efficiency (FE) of 93.2 ± 2.9% and a remarkable partial current density of 326.0 ± 10.3 mA cm−2. The Pb-PEG catalyst also exhibits a stable formate FE of over 80% for 100 h, resulting in the production of ∼693 mmol formate. The morphology engineering by PEG maintains the lamellar morphology of Pb nanosheets to expose more active sites. Density functional theory calculations reveal that the tailored reaction microenvironment created by vicinal PEG ligands acts as a catalytic reservoir which facilitates CO2 adsorption and stabilizes the formation of the *OCOH intermediate, thus resulting in the impressive formate production.

Iridium Nanosheet Catalysts Supported on Titanium Oxide for Oxygen Evolution Reaction in Polymer Electrolyte Membrane Water Electrolysis

In order to overcome the disadvantage of intermittent production of renewable energy, Polymer electrolyte membrane water electrolysis(PEMWE), which is one of the technologies of producing hydrogen by electrolyzing water, is attracting attention. For the commercialization of PEMWE, it is important to reduce usage of iridium(Ir) for oxygen evolution reaction(OER) in the anode electrode. Many studies have been reported to reduce the amount of iridium used by developing a catalyst with higher performance than the iridium nanoparticle catalyst used as a commercial catalyst. As one of the strategies, the introduction of support materials that can increase the active area of the catalyst is drawing attention. While carbon-based supports are mainly used in other applications, in OER environments, carbon is easily corroded due to high voltage and strong acid conditions. Therefore, it is necessary to use a metal oxide support with high corrosion resistance. In particular, titanium oxide(TiO2) is one of the suitable support candidates because it is a stable material in an acidic OER environment. However, catalysts loaded on TiO2 with nanoparticles cause an electrical contact problem due to the low electrical conductivity of TiO2, which causes a degradation in activity. Many studies have reported doping methods to increase the conductivity of TiO2, but there are also reports that these methods reduce the durability of support. Thus, a new approach to synthesizing a better structure of catalysts is needed to utilize metal oxide support.Herein, we present an approach to iridium nanosheet (NS) catalysts supported on TiO2(Ir NS/TiO2). Ir NSs were synthesized by an facile method by directly annealing a mixture of Ir precursor and alkali salt. Ir NSs were supported on TiO2 to be utilized as a reaction site and also acts as an electron path to compensate for the low electrical conductivity of TiO2. Ir NS/TiO2 showed superior OER activity and stability under acidic conditions. These results showed that Ir NS/TiO2 could be utilized to reduce the amount of precious metal catalyst in PEMWE and increase the stability of OER supported catalysts.

Simultaneous Boosting Nitrogen Reduction Activity and Suppressing Hydrogen Evolution Reaction Activity of Transition Metal Oxide Based Electrocatalyst

Ammonia (NH3) is widely served as fertilizer, safer chemical hydrogen storage, and energy conservation materials with an annual production around 200 million tons per year. Currently, NH3 is mainly synthesized via the Haber-Bosch process, which is an extremely energy- and capital-intensive (high temperature 400–500 °C and high pressure 100–350 atm) process, consuming over 1% of the global annual energy output, emitting massive amount of greenhouse gases (~420 Mt CO2 annually), and causing serious concerns with climate change. Electrochemical nitrogen reduction reaction (eNRR) allows NH3 production from nitrogen (N2) and water (H2O) under ambient conditions. Especially if driven by renewable energies, NRR represents a potentially clean and sustainable strategy for replacing the traditional Haber-Bosch process and alleviating climate change effect. One of the most critical fundamental challenges in production of ammonia via electrochemical nitrogen reduction reaction (eNNR) is developing catalysts which are capable to boost eNRR activity and concurrently suppress the overwhelming competitive hydrogen evolution reaction (HER). This work reports a new strategy to develop such catalysts to alleviate this challenge. This new strategy for the first time takes advantage of the outstanding capability of some redox active transition metal oxides (TMOs) in their super capability in electrochemically controlled proton interstitial doping and the associated remarkable structural changes to boost their NRR activity. Further, inspired by their unique hydrogen intercalation determined HER activity, this new strategy introduced cationic substitutional doping of the TMOs with nonmetal elements, such as phosphorus (P), to modulate their proton intercalation behavior, achieving HER suppression. In this work, tungsten oxide nanosheets (WO3) have been exploited as a typical example of such TMOs to demonstrate the feasibility of this innovative strategy. It is found that cationic P doping also accompanies introduction of large quantity of oxygen vacancies (OVs) in the matrix of the WO3 and structural changes of the WO3 lattice. The synergy of the substitutional doping and interstitial doping in tuning the electronic and the local geometric structures leads to significantly enhanced eNNR performance of WO3 nanosheets. An unprecedented high Faradaic efficiency (FE) of 64.1% with NH3 yield of 24.5 µg h-1 has been reached, representing the highest NRR performance for WO3 based catalysts. It is worth mentioning that the P-doped WO3 catalyst (200 nm square with a thickness of 20-40 nm) is much larger than most of the reported catalyst. The catalytic yield is even higher than that achieved with atomic thin two-dimensional (2D) WO3 nanosheets (OV-rich) catalysts (17 µg h-1 with a FE of 7.0%), which is known for their high catalytic efficiency due to the excellent accessibility of all the catalytic active sites. It is also worthwhile to mention that the FE of 64.1% is comparable to that of the natural nitrogenase can be reached (65%), which is unprecedented high compared to most of catalysts reported so far (<25%). In addition, inclusion of Li ions in the electrolyte further increased the NH3 yield to 60.1 µg h-1 with the high FE largely remained, reached the highest eNNR performance for all the TMO based catalysts. Density functional theory calculations further revealed the synergistic role of interstitial doping of H* and substitutional cationic doping of P, and the associated generation of OVs in increasing the electronic states crossing the Fermi level of the WO3 and thus reducing reaction energy barrier in N2 activation and hydrogenation. An interesting non-PCET (proton coupled electron transfer) mechanism is revealed in the first step and the rate determining step during eNNR, providing a new design principle for TMO-based catalysts. Figure 1

Highly efficient electrosynthesis of H2O2 in acidic electrolyte on metal-free heteroatoms co-doped carbon nanosheets and simultaneously promoting Fenton process

Recently electrochemical synthesis of H2O2 through oxygen reduction reaction (ORR) via 2e− pathway is considered as a green and on-site route. However, it still remains a big challenge for fabricating novel metal-free catalysts under acidic solutions, since it suffers from high overpotential due to the intrinsically week *OOH adsorption. Herein, a co-doped carbon nanosheet (O/NC) catalyst toward regulating O and N content was synthesized for improving the selectivity and activity of H2O2 electrosynthesis process. The O/NC exhibits outstanding 2e− ORR performance with low onset potential of 0.4 V (vs. RHE) and a selectivity of 92.4% in 0.1 mol/L HClO4 solutions. The in situ electrochemical impedance spectroscopy (EIS) tests reveals that the N incorporation contributes to the fast ORR kinetics. The density functional theory (DFT) calculations demonstrate that the binding strength of *OOH was optimized by the co-doping of oxygen and nitrogen at certain content, and the O/NCCOOH site exhibits a lower theoretical overpotential for H2O2 formation than OCCOOH site. Furthermore, the promoted kinetics for typical organic dye degradation in simultaneous electron-Fenton process on O/NC catalyst was demonstrated particularly for broadening its environmental application.