Efficient Active Sites Research Articles

Facilely prepared Co-based MOF functionalized N, S-doped reduced graphene oxide for electrochemical non-enzymatic glucose sensing

Rational design of modified electrode materials is critical for electrochemical sensors. Metal-organic frameworks (MOFs), a novel sort of substance with porosity, has received widespread attention owing to various superior characteristics such as adjustable pore sizes, great surface area and controllable structures. Nevertheless, the poor charge transfer capability of MOFs leads to a general suppression of their electrochemical sensing performance. To solve this issue, compositing conductive substance with MOFs have been demonstrated to be an effective strategy. Herein, Co-based MOF (ZIF-67) functionalized N, S-doped reduced graphene oxide (N, S-RGO) heterostructure (ZIF-67/N, S-RGO) was fabricated through an in-situ synthesis method. The composite material was used in the modification of an electrode to construct a sensing platform for non-enzymatic glucose testing. The synergistic interaction of ZIF-67 and N, S-RGO not only provided more efficient active sites and larger surface areas, but also improved the electron transport efficiency and electrocatalytic performance. Under optimized conditions, the ZIF-67/N, S-RGO/GCE had a dynamic linear range of 1–3200 μM, with a detection limit of 0.33 μM (S/N = 3) for glucose detection. The sensing platform also provided excellent reproducibility, selectivity, and stability (70 % activity retained after 12 days). Furthermore, the sensor had the potential to apply for glucose determination in human serum. This work presented a novel strategy to the field of non-enzymatic glucose sensing and may provide effective coaching for optimizing the electrochemical sensing performance of other series of MOFs.

Photocatalytic Nitrogen Fixation Coupled with the Generation of Value-Added Chemicals from N2 and Cellulose over MoO3 Nanosheets.

Photocatalytic nitrogen fixation from N2 provides an alternative strategy for ammonia (NH3) production, but it was limited by the consumption of a sacrificial electron donor for the currently reported half-reaction system. Here, we use naturally abundant and renewable cellulose as the sacrificial reagent for photocatalytic nitrogen fixation over oxygen-vacancy-modified MoO3 nanosheets as the photocatalyst. In this smartly designed photocatalytic system, the photooxidation of cellulose not only generates value-added chemicals but also provides electrons for the N2 reduction reaction and results in the production of NH3 with a maximum rate of 68 μmol·h-1·g-1. Also, the oxygen vacancies provide efficient active sites for both cellulose oxygenolysis and nitrogen fixation reactions. This work represents useful inspiration for realizing nitrogen fixation coupled with the generation of value-added chemicals from N2 and cellulose through a photocatalysis strategy.

Enhanced electrochemical nitrate reduction on copper nitride with moderate intermediates adsorption

Nitrate in surface and underground water caused systematic risk to the ecological environment. The electrochemically reduction of nitrate into ammonia (NO3RR), offering a sustainable route for nitrate containing wastewater treatment and ammonia fertilizer conversion. Exploration of catalyst with improved catalytic activity with lower energy barriers is still challenging. Here, we report a copper nitride (Cu3N) catalyst with moderate *NOx and *H2O intermediates adsorptions showed enhanced NO3RR performance. Density functional theory calculations reveals that the unique electronic structure of Cu3N provides efficient active sites for NO3RR, thus enabled balanced adsorption of *NO3 and *H2O (ΔE descriptor), sufficient active hydrogen, and moderate intermediate (*NO3 → HNO3, *NH2→*NH3) adsorption energy. Notably, the in-situ analysis technology revealed potential-driven reconstruction and rehabilitation of Cu3N, forming possible nitrogen vacancy, thus implied for better mechanism understanding. The NO3RR activity of Cu3N surpasses that of most recent catalysts and demonstrates superior stability and implies the application for NH4+ fertilizer recovery, which maintaining an NH3 Faradaic efficiency of 93.1 % and high yield rate of 2.9 mg cm2h−1 at −0.6 V versus RHE. These findings broaden the application scenarios of Cu3N catalyst for ammonia synthesis and provide strategy on improving NO3RR performance.

A novel Cu-based covalent organic framework with Cu-N2O2 single sites for efficient CO2 electroreduction to methane

Single-site catalysts (SSCs) are useful for CO2 electroreduction (CO2ER) to methane (CH4), but their selectivities for CH4 are still unsatisfactory due to the lack of efficient active sites. Herein, a novel Cu-based covalent organic framework (CuN2O2-COF) with Cu-N2O2 single sites was synthesized by the Schiff base reaction and used in CO2ER to improve CH4 generation for the first time. Compared with typical SSCs containing Cu-N4 or Cu-O4 sites, CuN2O2-COF exhibited superior CH4 production efficiency in CO2ER: the Faradaic efficiency of CH4 was as high as 85.4%, and the CH4 partial current density reached 313 mA·cm−2 at −1.3 V, which exceeded those of most electrocatalysts reported thus far. Theoretical calculations indicated that compared with the Cu-N4 or Cu-O4 sites in typical SSCs, the new Cu-N2O2 configuration in CuN2O2-COF increased the d‐band center of the Cu sites and enhanced the adsorption of key intermediates (*COOH and *CHO) required for CO2ER to CH4.

Fluorine-decoration induced deep reconstruction of iron cobalt oxide for high-efficiency oxygen evolution reaction

The oxygen evolution reaction (OER) is a pivotal process in water electrolysis systems, yet developing cost-effective and highly active OER electrocatalysts from earth-abundant materials through straightforward methods remains a formidable challenge. In this study, FeCo oxides and their fluorides are synthesized using a one-step room-temperature process followed by fluorination with fluorine gas. We compared the OER performance of Fe, Co, and FeCo oxides and investigated the impact of fluorine doping on their physical properties and OER efficiency. Results revealed that the FeCo–O bimetallic oxide exhibited an overpotential of 370 mV in an alkaline electrolyte at a current density of 10 mA/cm2, significantly surpassing the performance of monometallic Fe–O (1 V) and Co–O (467 mV). Fluorine modification markedly enhanced the OER activity of these materials, with Fe-OF at 570 mV, Co-OF at 330 mV, and FeCo-OF at 285 mV. Notably, FeCo-OF demonstrated a stable overpotential lower than commercial RuO2 (289 mV) during a continuous 12 h OER test. Electrochemical analyses and spectral characterizations indicated that fluorine ion electronic regulation facilitated efficient electrocatalytic active sites in the spent FeCo-OF catalyst through in situ self-reconstruction, leading to its stable and superior OER performance. Density functional theory (DFT) calculations confirmed that fluorine modification of the bimetallic oxides decreased the O* Gibbs free energy from 4.86 to 2.44 eV, thereby enhancing the kinetics of the OER reaction.

Identifying Pd9OX as the optimum catalyst for the direct synthesis of H2O2 through microkinetic modeling with coverage effects

Identifying efficient active sites for the direct synthesis of hydrogen peroxide over Pd-based catalysts has been a subject of considerable debate. In this study, we employ particle swarm optimization method and density functional theory to explore the H2O2 synthesis mechanism on Pd, PdO, and the partially oxidized surface (Pd9OX). A comprehensive mechanism for Pd9OX is elucidated, and subsequent coverage-dependent kinetic analysis allows for a quantitative assessment of catalytic performance at the interphase. Our findings conclusively establish that the interphase between Pd and PdO represents the optimal active site. Phase diagram analysis further aids in determining stable structures under reaction conditions. At 298.15 K and under oxygen balance, the Pd9O6 surface remains stable throughout the reaction, demonstrating high activity and selectivity. This work underscores the significance of the interphase in comprehending catalytic performance and unveils promising avenues for optimizing catalyst performance by controlling reaction conditions and surface composition.

Near-range modulation of single-atomic Fe sites by simultaneously integrating heteroatom and nanocluster for efficient oxygen reduction

Modulation strategies are widely developed to regulate electronic state of single-atom catalysts (SACs) to reinforce the catalytic activity of oxygen reduction reaction (ORR). However, the modulation effect using only single coordination regulation is often insufficient to optimize the electronic and geometric structure of metal active centers. Herein, a general strategy to modify the activity of single-atomic Fe site is achieved by dual decoration of Fe centers with contiguous sulfur atoms and metal nanoclusters via an aggregation-redispersion route. Under near-range engagement, the adjacent S atoms and Fe nanoclusters can break the symmetric electronic interface of Fe-N moiety, and act as the modulators to synergistically tune the electronic configurations of Fe centers, leading to less electron transfer to *OH, and subsequent favorable desorption. In situ spectroscopic characterization and theoretical results reinforces the significant roles of S atoms and metal clusters in tandem by correlating their induced electron redistribution with ORR activity, which ultimately accelerates the adsorption/desorption of oxygenated intermediates for robust catalytic performance. Due to the improvement of graphitization degree, carbon supports possess efficient active sites and exhibit superior anti-corrosion. The resultant FeNC-2 M demonstrates outstanding ORR activity with high power density, maintaining remarkable durability in Zn-air batteries and microbial fuel cells. This work provides effective and universal way to modulate microenvironment of single metal sites, facilitating the open up of potential application spaces for various SACs.

Bifunctional S-scheme Fe7S8/CuIn5S8 heterostructures with S-vacancies for boosted photocatalytic antibiotic degradation and hydrogen evolution

The reasonable designing, interfacial tuning and construction of S-scheme heterostructures offering high performance water pollutants treatment and energy production still remains challenging. Following the structure, band structure and interface function perspective, we prepared Fe7S8/CuIn5S8 heterostructures photocatalysts with sulfur vacancies for superior norfloxacin (NOR) degradation and hydrogen production under visible light. In particular, for optimal 30FS/CIS (30%Fe7S8/CuIn5S8), the H2 evolution was up to 35.6 mmol g−1 h−1 which was 11.5 times than pristine Fe7S8 with TEOA as sacrificial agent. The heterojunction could also show 98.7% degradation of NOR in 90 min under visible light. Interestingly, using NOR pollutant as sacrificial agent under synergistic conditions, 22.7 mmol g−1 h−1 H2 evolution and 98.9% degradation of NOR (in 45 min) was achieved. The significantly boosted photocatalytic pollutant degradation and hydrogen generation performance over Fe7S8/CuIn5S8 hybrids is ascribed to the efficient S-scheme charge transfer and active sites provided by sulfur vacancies (Vs). The deep electron transfer mechanism and the charge transfer efficiency were supported by in-situ XPS, UPS, electrochemical experiments and photoluminescence. Experimental results including scavenging tests and ESR findings provided the direct evidence of photogenerated holes and ●OH radicals for pollutant degradation and electrons in hydrogen generation. This work contributes to effective designing and developing high-activity visible light/solar light assisted heterojunction photocatalysts for realizing superior clean energy generation and pollutant degradation.

Layered Double Hydroxide Derivatives for Polyolefin Upcycling.

While Ru-catalyzed hydrogenolysis holds significant promise in converting waste polyolefins into value-added alkane fuels, a major constraint is the high cost of noble metal catalysts. In this work, we propose, for the first time, that Co-based catalysts derived from CoAl-layered double hydroxide (LDH) are alternatives for efficient polyolefin hydrogenolysis. Leveraging the chemical flexibility of the LDH platform, we reveal that metallic Co species serve as highly efficient active sites for polyolefin hydrogenolysis. Furthermore, we introduced Ni into the Co framework to tackle the issue of restricted hydrogenation ability associated with contiguous Co-Co sites. In-situ analysis indicates that the integration of Ni induces electron transfer and facilitates hydrogen spillover. This dual effect synergistically enhances the hydrogenation/desorption of olefin intermediates, resulting in a significant reduction in the yield of low-value CH4 from 27.1 to 12.6%. Through leveraging the unique properties of LDH, we have developed efficient and cost-effective catalysts for the sustainable recycling and valorization of waste polyolefin materials.

Anthraquinone-based polymer modified BiVO4 photoanode with strong electron-withdrawing functional groups for boasting photoelectrochemical water oxidation

The photoelectrochemical (PEC) performance ofBiVO4 is limited by sluggish water oxidation kinetics and severe carrier recombination. Herein, a novel high-performance BiVO4/NiFe-NOAQ photoanode is prepared by a simple one-step hydrothermal method, using BiVO4 and 1-Nitroanthraquinone (NOAQ) as raw materials. The BiVO4/NiFe-NOAQ photoanode has an excellent photocurrent density of 5.675 mA cm−2 at 1.23 VRHE, which is 3.35 times higher than that of the pure BiVO4 (1.693 mA cm−2) photoanode. The BiVO4/NiFe-NOAQ shows a significant improvement in charge separation efficiency (86.12 %) and charge injection efficiency (87.86 %). The improvement is ascribable to the NiFe-NOAQ form a type II heterojunction with BiVO4 to inhibit carrier recombination. More importantly, the kinetic isotope experiment suggests that the proton-coupled electron transfer (PCET) process can enhance the charge transfer of BiVO4/NiFe-NOAQ. The contact angle measurements show that modifying functional groups enhanced the hydrophilicity of BiVO4/NiFe-NOAQ, which can further accelerate the PCET process. The XPS and PL results as well as the tauc plot indicate that the strong electron-withdrawing ability of –NO2 which can promote the extension of π conjugation, results in more π electron delocalization and produces more efficient active sites, thus achieving efficient photoelectrochemical water oxidation.

Active and stable Co[sbnd]Ox sites promote peroxymonosulfate activation for sulfamethoxazole degradation through nonradical pathways

Cobalt (Co) single-atom sites are considered as the most efficient active sites in peroxymonosulfate (PMS) based advanced oxidation processes. However, CoO configurations instead of Co-N configurations were scarcely explored. Herein, isolated Co single atoms were successfully implanted onto hydroxyl decorated UiO-66 (Co/UiO-66-220) to generate [Zr6O4(OH)4(BDC)5.35(OH)1.30(OH2)1.30] structure to form {ZrOCoOZr} single-site through coordination strategy. Owing to the strong electron transfer ability of CoOx sites, the Co/UiO-66-220/PMS system displayed outstanding degradation performance and 100 % sulfamethoxazole (SMX) degradation efficiency was achieved within 10 min. Remarkably, the system also displayed excellent degradation performance in the presence of anions and complex actual wastewater. The membrane system was particularly effective, achieving a 90.32 % removal efficiency within 240 min. The nonradical species, singlet oxygen (52.8 %), electron transfer (4.9 %) and high-valent cobalt-oxo species (Co (IV) = O) (23.9 %), were dominated in the degradation process. The generated intermediates are low-toxicity. The results demonstrate the excellent activity of CoOx sites for PMS activation and its practical application potential for remediation of organic contaminants.

Electronic structure modulation of iron sites with fluorine coordination enables ultra-effective H2O2 activation

Electronic structure modulation of active sites is critical important in Fenton catalysis as it offers a promising strategy for boosting H2O2 activation. However, efficient generation of hydroxyl radicals (•OH) is often limited to the unoptimized coordination environment of active sites. Herein, we report the rational design and synthesis of iron oxyfluoride (FeOF), whose iron sites strongly coordinate with the most electronegative fluorine atoms in a characteristic moiety of F-(Fe(III)O3)-F, for effective H2O2 activation with potent •OH generation. Results demonstrate that the fluorine coordination plays a pivotal role in lowering the local electron density and optimizing the electronic structures of iron sites, thus facilitating the rate-limiting H2O2 adsorption and subsequent peroxyl bond cleavage reactions. Consequently, FeOF exhibits a significant and pH-adaptive •OH yield (~450 µM) with high selectivity, which is 1 ~ 3 orders of magnitude higher than the state-of-the-art iron-based catalysts, leading to excellent degradation activities against various organic pollutants at neutral condition. This work provides fundamental insights into the function of fluorine coordination in boosting Fenton catalysis at atomic level, which may inspire the design of efficient active sites for sustainable environmental remediation.

Room‐Temperature, Meter‐Scale Synthesis of Heazlewoodite‐Based Nanoarray Electrodes for Alkaline Water Electrolysis

AbstractAlkaline water electrolysis is among the most promising technologies to massively produce green hydrogen. Developing highly‐active and durable electrodes to catalyze the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) is of primary importance. Here a facile, room‐temperature synthetic route is presented to access heazlewoodite phase (Ni, Fe)3S2 nanosheet arrays supported on NiFe foam (NFF), whose production can be easily scaled up to meter size per batch operation. The (Ni, Fe)3S2/NFF electrode can serve as a high‐performance electrocatalyst for both HER and OER in alkaline media, and remains highly stable for over 1000 h at 100 mA cm−2 current densities. When working as HER electrocatalyst, (Ni, Fe)3S2 is confirmed as catalytic phase that provides a high density of efficient active sites (e.g., Ni─Ni and Ni─Fe bridge sites). During electrochemical OER testing, (Ni, Fe)3S2 nanosheets totally transform into γ‐(Fe, Ni)OOH as active catalytic phase for OER. As a consequence, the (Ni, Fe)3S2/NFF can be used to integrate into an alkaline electrolyzer as both the cathode and anode, and to give an excellent catalytic performance (600 mA cm−2 @1.93 V), which is better than the alkaline electrolyzer based on commercial Raney Ni electrodes.

Advanced Carbon Electrocatalysts for Selective Oxygen Reduction into Hydrogen Peroxide: Understandings of Active Sites

Review Advanced Carbon Electrocatalysts for Selective Oxygen Reduction into Hydrogen Peroxide: Understandings of Active Sites Jiaxin Su 1,2, Bingbing Xiao 1,2, Jun Wang 1,2,* and Xiaofeng Zhu 1,2,* 1 State Key Laboratory of Environment-Friendly Energy Materials, School of Materials and Chemistry, Southwest University of Science and Technology, Mianyang 621010, China 2 Tianfu Institute of Research and Innovation, Southwest University of Science and Technology, Chengdu 610299, China * Correspondence: junwang091@163.com (J.W.); xfzhu@swust.edu.cn (X.Z.) Received: 17 January 2024; Revised: 25 January 2024; Accepted: 19 February 2024; Published: 5 March 2024 Abstract: Electrochemical conversion of oxygen-to-hydrogen peroxide (H2O2) through oxygen reduction (ORR) is becoming a green and effective solution to replacing conventional anthraquinone industry. Advanced carbon is currently one of the most promising catalysts for H2O2 electrosynthesis by a selective two-electron ORR (2e-ORR), owing to its chemical and catalytic merits. To realize better performance of 2e-ORR over advanced carbons, extensive efforts is devoted to constructing highly efficient carbon-based active sites, which requests in-depth understanding of their underlying catalytic roles. Here, an informative and critical review of recent investigations on active sites on advanced carbons for 2e-ORR is provided. Together with our recent findings, the review first highlights the promoting progress on heteroatom-doped carbons, and their direct/indirect contributions for 2e-ORR has been emphasized. Simultaneously, defect engineering of carbon scaffold is briefly demonstrated as a practical strategy for achieving outstanding H2O2 production. Meanwhile, the review also offers analysis on striking influence of surface modification for carbon active site. Finally, challenges and perspectives of the advanced carbon catalysts for 2e-ORR are outlined. Such reviewed fundamentals of active sites in this emerging field would shed light to future impactful progress in ORR and broader research of energy and catalysis.

Cobalt‐based Co3Mo3N/Co4N/Co Metallic Heterostructure as a Highly Active Electrocatalyst for Alkaline Overall Water Splitting

AbstractAlkaline water electrolysis holds promise for large‐scale hydrogen production, yet it encounters challenges like high voltage and limited stability at higher current densities, primarily due to inefficient electron transport kinetics. Herein, a novel cobalt‐based metallic heterostructure (Co3Mo3N/Co4N/Co) is designed for excellent water electrolysis. In operando Raman experiments reveal that the formation of the Co3Mo3N/Co4N heterointerface boosts the free water adsorption and dissociation, increasing the available protons for subsequent hydrogen production. Furthermore, the altered electronic structure of the Co3Mo3N/Co4N heterointerface optimizes ΔGH of the nitrogen atoms at the interface. This synergistic effect between interfacial nitrogen atoms and metal phase cobalt creates highly efficient active sites for the hydrogen evolution reaction (HER), thereby enhancing the overall HER performance. Additionally, the heterostructure exhibits a rapid OH− adsorption rate, coupled with great adsorption strength, leading to improved oxygen evolution reaction (OER) performance. Crucially, the metallic heterojunction accelerates electron transport, expediting the afore‐mentioned reaction steps and enhancing water splitting efficiency. The Co3Mo3N/Co4N/Co electrocatalyst in the water electrolyzer delivers excellent performance, with a low 1.58 V cell voltage at 10 mA cm−2, and maintains 100 % retention over 100 hours at 200 mA cm−2, surpassing the Pt/C||RuO2 electrolyzer.

Cobalt-based Co3Mo3N/Co4N/Co Metallic Heterostructure as a Highly Active Electrocatalyst for Alkaline Overall Water Splitting.

Alkaline water electrolysis holds promise for large-scale hydrogen production, yet it encounters challenges like high voltage and limited stability at higher current densities, primarily due to inefficient electron transport kinetics. Herein, a novel cobalt-based metallic heterostructure (Co3Mo3N/Co4N/Co) is designed for excellent water electrolysis. In operando Raman experiments reveal that the formation of the Co3Mo3N/Co4N heterointerface boosts the free water adsorption and dissociation, increasing the available protons for subsequent hydrogen production. Furthermore, the altered electronic structure of the Co3Mo3N/Co4N heterointerface optimizes ΔGH of the nitrogen atoms at the interface. This synergistic effect between interfacial nitrogen atoms and metal phase cobalt creates highly efficient active sites for the hydrogen evolution reaction (HER), thereby enhancing the overall HER performance. Additionally, the heterostructure exhibits a rapid OH- adsorption rate, coupled with great adsorption strength, leading to improved oxygen evolution reaction (OER) performance. Crucially, the metallic heterojunction accelerates electron transport, expediting the afore-mentioned reaction steps and enhancing water splitting efficiency. The Co3Mo3N/Co4N/Co electrocatalyst in the water electrolyzer delivers excellent performance, with a low 1.58 V cell voltage at 10 mA cm-2, and maintains 100 % retention over 100 hours at 200 mA cm-2, surpassing the Pt/C||RuO2 electrolyzer.

Rational Construction of 3D Self-Supported MOF-Derived Cobalt Phosphide-Based Hollow Nanowall Arrays for Efficient Overall Water Splitting At large Current Density.

Developing efficient nonprecious bifunctional electrocatalysts for hydrogen and oxygen evolution reactions (HER and OER) in the same electrolyte with a low overpotential and large current density presents an appealing yet challenging goal for large-scale water electrolysis. Herein, a unique 3D self-branched hierarchical nanostructure composed of ultra-small cobalt phosphide (CoP) nanoparticles embedded into N, P-codoped carbon nanotubes knitted hollow nanowall arrays (CoPʘNPCNTs HNWAs) on carbon textiles (CTs) through a carbonization-phosphatization process is presented. Benefiting from the uniform protrusion distributions of CoP nanoparticles, the optimum CoPʘNPCNTs HNWAs composites with high abundant porosity exhibit superior electrocatalytic activity and excellent stability for OER in alkaline conditions, as well as for HER in both acidic and alkaline electrolytes, even under large current densities. Furthermore, the assembled CoPʘNPCNTs/CTs||CoPʘNPCNTs/CTs electrolyzer demonstrates exceptional performance, requiring an ultralow cell voltage of 1.50V to deliver the current density of 10mAcm-2 for overall water splitting (OWS) with favorable stability, even achieving a large current density of 200mAcm-2 at a low cell voltage of 1.78V. Density functional theory (DFT) calculation further reveals that all the C atoms between N and P atoms in CoPʘNPCNTs/CTs act as the most efficient active sites, significantly enhancing the electrocatalytic properties. This strategy, utilizing 2D MOF arrays as a structural and compositional material to create multifunctional composites/hybrids, opens new avenues for the exploration of highly efficient and robust non-noble-metal catalysts for energy-conversion reactions.

S-scheme homojunction and activate site engineering over TiO2 for highly efficient photocatalytic nitrogen fixation

The presence of efficient catalytic active sites and an ample supply of electrons are the two indispensable factors for achieving photocatalytic nitrogen fixation. Herein, the Fe-doped TiO2 S-scheme anatase/rutile homojunction (F-T-A/R) was synthesized as a brilliant photocatalyst for photocatalytic nitrogen fixation from N2 to NH3 under ambient atmosphere. The optimized F-T-A/R photocatalyst (A/R = 98:2, Fe-2 wt%) exhibits an unprecedented NH3 generation rate of 358 μmol gcat-1h−1 in water solvent and under simulated solar light irradiation. Experimental and theoretical studies reveal that the constructed S-scheme homojunction in F-T-A/R is conducive to fluent charge separation and adequate supply of electrons on rutile with higher nitrogen fixing activity, while the tuned local electronic structure of oxygen vacancy with Fe doping is engineered to strengthen active sites, synergistically enhancing the photocatalytic nitrogen fixation.

Insitu formation of low-valence state cobalt cation in octahedral sites of Co9S8 for highly efficient electrocatalytic hydrogen evolution

The elementary valence state in electrocatalysts has been demonstrated to significantly affect their catalytic ability. However, enhancing performance by controlling the elemental valence state and the precise doping location remains challenging. This work is devoted to exploring a controllable electronic structure that is capable of improving electrocatalytic hydrogen evolution activity by manipulating the valence state of an element at a specific location. This is demonstrated by reducing the high valence state Co3+ in octahedral sites of Co9S8 to form low valence state Co2+ using sodium borohydride. The occupation of Co2+ in the Co3+ site gives rise to the generation of local lattice distortion, which provides more efficient active sites for the hydrogen evolution reaction (HER). Additionally, Co2+ in octahedral sites donates more electrons to adsorbed water molecules, which facilitates HO–H dissociation and H∗ adsorption. The resulting electrocatalyst exhibits a low overpotential of 301 mV at 500 mA/cm2 for the HER, which is the best performance among all reported single-component Co9S8-based catalysts. This work paves an avenue for the rational design of HER electrocatalysts by precisely tuning the valence state of elements at specific locations.

Oxygen Vacancies Riched PrOx Polycrystalline Nanorods on Graphene Nanosheets as Advanced Oxygen Catalysts for Lithium‐Oxygen Batteries

AbstractThe slow reaction kinetics of Li−O is currently the most pressing technical obstacle to the development of lithium‐oxygen batteries. The Li2O2′s growth/decomposition pathways dominate the battery performance and can be optimized by exploring efficient cathode catalysts. Herein, we prepare regular, polycrystalline, oxygen vacancy (VO)‐riched PrOx uniformly anchored on few‐layered graphene (FLG) nanosheets to boost the Li−O reactions. XRD, TGA, XPS, SEM, TEM, SEAD, and electrochemical test techniques are used to study their chemical composition, microstructure, battery performance, and the effect of FLG on the formation of polycrystalline and VO. It is confirmed that FLG provides a large specific surface area and good electron transport. Moreover, it works as an anchoring substrate to transform PrOx from single crystal to polycrystalline, which is beneficial for exposing catalytic sites and VO and improving the battery performance. This unique composition and structure offer efficient active sites, accelerate electron transport, and regulate the Li2O2′s nucleation to form nanofilms or nanosheets on the catalyst. With this cathode catalyst, the battery achieved an ultralow total overpotential of 0.618 V, with a discharge capacity of 11489 mAh g−1 in the ultimate‐capacity mode and a superior cyclability of 85 cycles under the limited capacity of 500 mAh g−1.