Intrinsic Catalytic Activity Research Articles

Manipulating Orbital Hybridization of CoSe2 by S Doping for the Highly Active Catalytic Effect of Lithium-Sulfur Batteries.

In recent years, various transition metal compounds have been extensively studied to deal with the problems of slow reaction kinetics and the shuttle effect of lithium-sulfur (Li-S) batteries. Nevertheless, their catalytic performance still needs to be further improved by enhancing intrinsic catalytic activity and enriching active sites. Doping is an effective means to boost the catalytic performance through adjusting the electron structure of the catalysts. Herein, the electron structure of CoSe2 is adjusted by doping P, S with different p electron numbers and electronegativity. After S doping (S-CoSe2), the content of Co2+ increases, and charge is redistributed. Furthermore, more electrons are transferred between Li2S4/Li2S and S-CoSe2, and optimal Co-S bonds are formed between them with optimized d-p orbital hybridization, making the bonds of Li2S4/Li2S the longest and easy to break and decompose. Consequently, the Li-S batteries with the S-CoSe2-modified separator achieve improved rate performance and cycling performance, benefiting from the better bidirectional catalytic activity. This work will provide reference for the selection of the anion doping element to enhance the catalytic effect of transition metal compounds.

Superhydrophilic and Underwater Superaerophobic Dual-Function Peony-Shaped Selenide Micro-nano Array Self-Supported Electrodes for High-Efficiency Overall Water Splitting Driven by Renewable Energy.

With the intensification of global environmental pollution and resource scarcity, hydrogen has garnered significant attention as an ideal alternative to fossil fuels due to its high energy density and nonpolluting nature. Consequently, the urgent development of electrocatalytic water-splitting electrodes for hydrogen production is imperative. In this study, a superwetting selenide catalytic electrode with a peony-flower-shaped micronano array (MoS2/Co0.8Fe0.2Se2/NixSey/nickel foam (NF)) was synthesized on NF via a two-step hydrothermal method. The optimal catalytic activity of cobalt-iron selenide was achieved by adjusting the Co/Fe ratio. The intrinsic catalytic activity of the electrodes was enhanced by incorporating transition metal selenides, which then served as a precursor for the subsequent loading of MoS2 nanoflowers on the surface to fully expose the active sites. Furthermore, the superwetting properties of the electrode accelerated electrolyte penetration and electron/mass transfer, while also facilitating bubble detachment from the electrode surface, thereby preventing "bubble shielding effect". This resulted in superior oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) performance, as well as overall water splitting capabilities. In a 1.0 M KOH solution, the electrode required only 166 and 195 mV overpotential to achieve a current density of 10 mA cm-2 for OER and HER, respectively. When functioning as a bifunctional catalytic electrode, only 1.60 V of voltage was necessary to drive the electrolyzer to reach a current density of 10 mA cm-2. Moreover, laboratory simulations of wind and solar energy-driven water splitting validated the feasibility of establishing a sustainable energy-to-hydrogen production chain. This work provides new insights into the preparation of low-overpotential, high-catalytic-activity superhydrophilic and underwater superaerophobic catalytic electrodes by rationally adjusting elemental ratios and exploring changes in electrode surface wettability.

Anchored Ru nanoclusters strategy enhances hydrogen spillover effect for high-efficiency hydrogen storage

Enhancing the hydrogen spillover effect of catalysts is an effective method for optimizing hydrogen storage reactions. In this study, we report a catalyst consisting of Ru nanoclusters (1.2–2.7 nm) anchored on nitrogen-doped carbon (NC) that are highly dispersed on an Al2O3 substrate. Both experimental and density functional theory-based calculations indicate that these constrained, highly dispersed ultrafine nanoclusters significantly improve the intrinsic catalytic activity of Ru and reduce the reaction barriers. Moreover, the electron transfer between NC and Ru clusters increases the adsorption inertness of Ru with hydrogen, enhances hydrogen desorption, and promotes hydrogen spillover, synergistically improving the activity of catalytic hydrogen storage. Notably, the aromatic compounds in the ethylene tar narrow fraction were effectively converted at a low temperature of 80 °C, and the total cycloalkanes yield reached 99.04 %. The hydrogen storage capacity can be about 5.70 wt%. Liquid Organic Hydrogen Carriers model compounds were fully hydrogenated at temperatures no higher than 70 °C with low Ru loading (2 wt%). This work provides a potential utilization strategy of ethylene tar narrow fraction as hydrogen carriers based on its hydrogenation over the highly active and stable Ru nanocluster catalysts.

Comparative electrocatalytic behavior of mesoporous FeP and FeS2 for the hydrogen evolution reaction

FeP nanoparticles and FeS2 nanospheres with mesoporous surface are synthesized, and their performance is compared for the hydrogen evolution reaction under identical electrochemical conditions. The activity-determining characteristics of the electrodes, such as specific and electrochemically active surface area, electrochemical impedance and charge transfer resistance, Tafel slopes, number of catalytic active sites, and turnover frequency (TOF) are studied and correlated to their activity. Because of its larger surface area and reduced charge transfer resistance, the FeS2 showed superior HER performance than the FeP, despite the latter’s higher intrinsic catalytic activity. The electrocatalytic stability of the electrocatalysts are also compared.

Highly active manganese nitride-europium nitride catalyst for ammonia synthesis

The development of efficient catalysts for ammonia synthesis under mild conditions is critical for establishing a carbon-neutral society powered by renewable ammonia. While significant effort has been focused on Fe and Ru-based catalysts, there have been very limited studies on manganese-based catalysts for ammonia synthesis because of their low intrinsic catalytic activity. Herein, we report that the synergy between manganese nitride (Mn4N) and europium nitride (EuN) yields an ammonia synthesis rate that is 41 and 25 times higher than that of neat Mn4N and EuN, respectively. Detailed studies suggest that a [Eu-N-Mn] species at the interface of Mn4N and EuN plays a pivotal role in ammonia synthesis. Compositing of Mn4N with other rare earth metal nitrides such as LaN, PrN, and CeN also leads to a significant enhancement in catalytic activity. This work broadens the scope of advanced nitride catalysts for ammonia synthesis.

Modulation of interface electric field over CoMoP-CoMoP2 heterostructure for high-efficiency oxygen evolution reaction

The construction of a heterostructure can significantly enhance the intrinsic activity of the electrocatalysts. In this study, a simple electrospinning combined with post-treatment strategy is successively employed to fabricate novel CoMoP-CoMoP2 heterostructure nanofibers. Experimental results and density functional theory (DFT) calculations demonstrate that the formation of CoMoP-CoMoP2 heterointerface can optimize the kinetics of the oxygen evolution reaction (OER) and enhance the intrinsic catalytic activity. As anticipated, the resulting CoMoP-CoMoP2 electrocatalyst displays outstanding OER performance (184 mV @ 10 mA cm−2, and 302 mV @100 mA cm−2) as well as excellent stability in 1 M KOH. Moreover, the OER test results of CoMoP-CoMoP2 with varying CoMoP and CoMoP2 contents indicate that CoMoP-CoMoP2-1 (with a mass ratio of approximately 1.01/10.1) exhibits the highest OER activity. Utilized as the overall water splitting electrocatalyst, CoMoP-CoMoP2-1 demonstrates exceptional durability and outperforms Pt/C||RuO2 electrolyzer, achieving a current density of 10 mA cm−2 and a battery voltage of only 1.53 V during continuous operation for 260 h. These findings suggest the practical application potential of this material, confirming the promising nature of bimetallic phosphide-bimetallic phosphide heterostructure electrocatalysts.

Directional Construction of Low-Coordination Fe-N3 Coupled with Intrinsic Carbon Defects for High-Efficiency Oxygen Reduction.

Regulating the coordination environment of Fe-Nx sites is an efficient but challenging approach for promoting the intrinsic catalytic activity of single-atom Fe/N-codoped carbon (Fe-N-C) toward the oxygen reduction reaction (ORR). Herein, low-coordination Fe-N3 sites coupled with carbon vacancies (Fe-N3/CV) are directionally constructed in Fe-N-C via pyrolysis of a metal-organic framework (MOF) precursor with N3-Zn-O-Fe moieties, which are delicately prefabricated by chemically anchoring Fe3+ onto a H2O-etching induced linker-missing Zn-N3 site in the MOF precursor. The optimized Fe-N-C with the Fe-N3/CV sites displays a high ORR half-wave potential of 0.92 V (vs RHE), which is attributed to the optimized electronic structure and binding strengths of the active Fe center toward the ORR intermediates stemming from the synergy of the asymmetric configuration of Fe-N3 as well as the adjacent carbon vacancies. This work could be enlightening for the design and construction of high-activity coupling sites in metal and nitrogen-codoped carbon catalysts.

Optimizing interactions for efficient hydrogen evolution reaction by incorporating rhenium nanoparticles on defect-rich carbon

The rich anchoring site on carbon renders it a promising support for catalytically active metal nanoparticles (NPs), thereby enhancing their intrinsic catalytic activity towards hydrogen evolution reaction (HER) through interactions between the support and the metal. However, complex synthesis conditions often compromise the synergy between the metal and support. Herein, we report Re NPs embedded on XC-72 carbon support to investigate the robust interactions in affecting the HER activity. Consequently, Re NPs anchored on defect-rich XC-72 exhibit efficient and robust HER activity in acidic conditions, achieving an extremely low overpotential of 25 mV to deliver a current density of 10 mA cm−2 and a Tafel slope of 78 mV dec−1, surpassing that of Pt/C catalyst. Based on experimental investigations and density functional theory calculations, the high catalytic activities of as-obtained Re/C can be attributed to the enhanced electron transport kinetics facilitated by the interactions between Re NPs and carbon support, the exposure of the active site on Re NPs, and lowered reaction energy barrier towards HER. This study provides valuable insights for the rational development of Re-based efficient catalysts for HER.

Constructing active lattice oxygen in high covalent perovskites for boosting catalytic activity

Transition-metal (TM) active centers are solely considered to probe the intrinsic origin of catalytic activity, but the interaction between metal and oxygen has been overlooked. Herein, an effective approach is demonstrated to adjust the degree of TM–O covalency, enhancing the intrinsic catalytic activity via Cu substitution and acid etching. In-situ spectroscopic investigations and theoretical calculations reveal that improved catalytic performances are attributed to enhanced TM–O covalency. Owing to the strong hybridization between TM 3d and O 2p orbitals, the intramolecular electrons are transported from oxygen to TM cations, promoting asymmetric electron redistribution and inducing oxygen holes (electrophilic O(2−δ)−) generation. Ligand oxygen holes as preactive oxygen centers achieved the initial activation of reactant molecules and lattice oxygen activation, ultimately boosting the heterogeneous catalytic activity. The findings highlight a new method to design highly covalent perovskite oxides with sufficient ligand oxygen holes to trigger lattice oxygen activation in the catalytic fields.

Electronic structure engineering of CNTs@NiFe-LDH composite via heteroatom doping for efficient seawater electrolysis

Exploring cost-effective, efficient, and durable bifunctional electrocatalysts for seawater splitting is crucial for green hydrogen production. Electronic structure engineering stands out as a promising method to tailor catalyst properties and enhance catalytic performance. In this work, a bifunctional composite, N-CNTs@NiFeZr-LDH, for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), is designed and fabricated. Results show that the incorporation of Zr into NiFe-LDH and N into CNTs generates a synergistic effect that optimizes the electronic structure of the composite, leading to a noticeable improvement in catalytic performance. Interestingly, a straightforward calcination treatment further enhances the catalytic performance. The optimized sample exhibits a current density of 100 mA cm−2 with ultra-low overpotentials of 210 and 185 mV for the HER and OER, respectively, in simulated seawater (1.0 M KOH + 0.5 M NaCl). When applied to overall water splitting in simulated seawater, a two-electrode electrolyzer assembled by the optimized sample achieves a current density of 350 mA cm−2 with only 1.65 V, and can operate steadily for 100 h. In natural seawater, the assembled electrolyzer delivers 350 mA cm−2 requiring only 1.68 V, together with an impressive stability. Besides offering an efficient bifunctional catalyst for seawater electrolysis, this work underscores the crucial role of electronic engineering in enhancing the intrinsic catalytic activity.

Microenvironment Tailoring of NiCo Alloys Coupled with FePc as Efficient Bifunctional Catalysts for High-Rate Zn-Air Batteries.

The practical application of Zn-air batteries require exploring cost-effective and durable bifunctional electrocatalysts. However, the simultaneous preparation of catalysts with bifunctional activities for oxygen reduction reaction (ORR) and oxygen precipitation reaction (OER) remains challenging. Herein, we synthesized a novel hybrid catalyst (FePc/NiCo/CNT), which couples NiCo alloy with FePc through electrostatic interaction. The interaction between FePc and NiCo alloy can enhance the intrinsic catalytic activity of the active site Fe-N4 and prevent the electrolyte corrosion of the metal alloy, ultimately improving the stability of the catalyst by the microenvironment-tailoring strategy. The resultant FePc/NiCo/CNT catalyst exhibits outstanding oxygen reduction reaction (ORR) activity with a half-wave potential of 0.88 V, which is attributed to the abundant Fe-Nx active sites. Furthermore, the electron interactions between NiCo/CNT and FePc accelerate electron transfer and enhance the activation of oxygen intermediates, consequently boosting the OER activity with an overpotential of 260 mV at 10 mA cm-2. The Zn-air batteries assembled with FePc/NiCo/CNT show a high power density of 175.1 mW cm-2 and excellent cycling stability for up to 430 h at 20 mA cm-2. The preparation of oxygen electrode catalysts for renewable clean energy devices can be made more convenient with this directly engineered strategy for ORR and OER active centers.

Refining Mn(III) Active Sites in MnO2-Based Self-Assembled Electrodes Via Oxygen Vacancy Induction to Enhance Oxygen Reaction Performance in Zinc-Air Batteries

Rechargeable zinc-air batteries are considered as a promising candidate for next-generation electrochemical energy conversion devices due to their safety, low cost, and high theoretical capacity/ energy density. Over the past few decades, α-MnO2-based electrodes have demonstrated their excellent performance and competitiveness in oxygen catalytic reactions. (1) According to eg filling theory, Mn(III) (t2g3eg1) sites in [MnO6] octahedral unit deliver superior bifunctional activity compared to Mn(II) (t2g3eg2) and Mn(IV) (t2g3eg0) sites.(2) However, the presence of unpaired single electrons of the Mn(III) site leads to low thermodynamic stability. Introducing oxygen vacancies to promote the electron rearrangement of the [MnO6] unit is a promising approach for enhancing the durability of Mn(III) active sites. Herein, we construct an oxygen-vacancy-enhanced MnO2-based electrode via a self-assembly process (NiCo2O4-MnO2@Ni foam). The intrinsic oxygen catalytic activity of NiCo2O4-MnO2@Ni foam is significantly improved by forming abundant highly stable Mn(III) active sites, which accelerate the mass transfer ability. As expected, the NiCo2O4-MnO2@Ni foam shows good bifunctional activity with a low overpotential of 0.69 V. The zinc-air battery assembled by NiCo2O4-MnO2@Ni foam exhibits a high peak power density of 576 mW cm-2, surpassing that of the Pt/C-Ir/C electrode. Additionally, benefiting from its stable flower-shaped hierarchical structure, the self-assembled electrode demonstrates long-term charge-discharge cycling stability, which lasts over 800 hours. This work provides innovative insights into enhancing MnO2-based electrodes by oxygen vacancy introduction.References N. Xu, Q. Nie, L. Luo, C. Z. Yao, Q. Gong, Y. Liu, X. Zhou, and J. Qiao, ACS applied materials & interfaces (2018).Z. Yin, R. He, H. Xue, J.-M. Chen, Y. Wang, X. Ye, N. Xu, J. Qiao and H. Huang, Energy Materials (2022).

The Role of Surface Roughening in Improving the Selectivity of Copper for CO2 Electroreduction

Electroreduction of CO2 (eCO2RR) has emerged as a promising alternative for production of renewable fuels and important commodity chemicals such as ethylene and ethanol. Simultaneously, it opens an economically attractive path to mitigate point sources of CO2, a potent greenhouse gas. Despite decades of research efforts, Cu remains the only catalyst capable of producing significant amounts of desirable C2+ products, containing more than one carbon atom. However, further improvement is needed for industrial applications. It is known that roughened copper-based electrocatalysts surfaces exhibit enhanced selectivity towards C2+ products during electroreduction of CO2. This poses a challenge for modeling efforts aiming to find a rationale for the enhanced selectivity. In this work, we use an innovative modeling approach to investigate roughened copper surfaces derived from cuprous oxide on structures of 100x100 nm2 size with atomic resolution and accuracy compared to density functional theory (DFT). We combine semilocal DFT (RPBE) in VASP, effective medium theory (EMT), and linear scaling relationships via the recently proposed alpha parameter scheme to investigate the site-resolved catalytic selectivity of copper sites. Electrode potential-dependence is included via the use of the VASPsol implicit solvation and a grand canonical potential approach. The approach allows us to investigate the effect of varied macroscopic roughness on the intrinsic catalytic activity of copper by comparing surfaces exposed to simulated sputtering and electropolishing, respectively. The study highlights i) the challenge for designing improved copper catalysts for CO2RR with monodisperse active site selectivity, ii) the need for careful experimentation when comparing to theory, and iii) the limitations of macroscopic roughness in controlling atomic scale activity.

(Invited) Atomically Dispersed Metal Electrocatalysts for CO2 to CO Conversion: From Single to Dual Metal Sites

Carbon-supported nitrogen-coordinated single-metal site catalysts (i.e., M−N−C, M: Fe, Co, or Ni) are active for the electrochemical CO2 reduction reaction (CO2RR) to CO.(1) We comprehensively engineered FeN4 and NiNx sites for electrochemical CO2 reduction to CO considering the particle sizes of the catalysts, metal content, and the M−N (M: Fe or Ni) bond structures.(2, 3)The unique M-N-C model allows us to elucidate each factor′s role exclusively regarding the promotion of CO2 reduction.(4)Optimal particle sizes and Fe content provide favorable external factors to improve mass activity. Structural changes of M−N bonds controlled by thermal activation temperatures can intrinsically enhance CO selectivity and kinetic activity. Notably, the NiN3 active sites with optimal local structures formed at higher temperatures (e.g., 1200 °C) are intrinsically more active and CO-selective than NiN4, providing a new opportunity to design a highly active catalyst via populating NiN3 sites with increased density. Further improving their intrinsic activity and selectivity by tuning their N−M bond structures and coordination is limited. We further expand the coordination environments of M−N−C catalysts by designing dual-metal active sites.(5)The Ni-Fe catalyst exhibited the most efficient CO2RR activity and promising stability compared to other combinations. Advanced structural characterization and theoretical prediction suggest that the most active N-coordinated dual-metal site configurations are 2N-bridged (Fe-Ni)N6, in which FeN4 and NiN4 moieties are shared with two N atoms. Two metals (i.e., Fe and Ni) in the dual-metal site likely generate a synergy to enable more optimal *COOH adsorption and *CO desorption than single-metal sites (FeN4 or NiN4) with improved intrinsic catalytic activity and selectivity.References Pan F, Zhang H, Liu K, Cullen D, More K, Wang M, et al. Unveiling Active Sites of CO2 Reduction on Nitrogen-Coordinated and Atomically Dispersed Iron and Cobalt Catalysts. ACS Catalysis. 2018;8(4):3116-22.Li Y, Adli NM, Shan W, Wang M, Zachman MJ, Hwang S, et al. Atomically dispersed single Ni site catalysts for high-efficiency CO2 electroreduction at industrial-level current densities. Energy & Environmental Science. 2022;15(5):2108-19.Mohd Adli N, Shan W, Hwang S, Samarakoon W, Karakalos S, Li Y, et al. Engineering Atomically Dispersed FeN4 Active Sites for CO2 Electroreduction. Angewandte Chemie International Edition. 2021;60(2):1022-32.Li J, Zhang H, Samarakoon W, Shan W, Cullen DA, Karakalos S, et al. Thermally Driven Structure and Performance Evolution of Atomically Dispersed FeN4 Sites for Oxygen Reduction. Angewandte Chemie International Edition. 2019;58(52):18971-80.Li Y, Shan W, Zachman MJ, Wang M, Hwang S, Tabassum H, et al. Atomically Dispersed Dual-Metal Site Catalysts for Enhanced CO2 Reduction: Mechanistic Insight into Active Site Structures. Angewandte Chemie International Edition. 2022;61(28):e202205632.

Plasma-Enhanced Copper Sulfide/Oxide Electrode for Zinc-Air/Copper Dual Mode Battery

As search for novel electrochemical energy storage systems continues, metal-air batteries are one of the possible solution. Consisting of a metal anode and an air-breathing cathode, by design, they achieve much higher gravimetric energy density in theory. However, s-orbital metals suffer passivation issues and poses safety threats due to their reactivity with air and humidity. As a solution to this issue, safer d-block metals are being studied as an alternative. Zinc air batteries (ZABs) utilizes earth-abundant and cost-effective zinc as its anode, and has high theoretical capacity. At its cathode, oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) occur during charging and discharge processes. Sluggish kinetics of ORR degrades the discharge performance, and is the bottleneck in commercial application of the zinc air battery. Additionally, irreversibility of the cathode reaction results in dissatisfactory retention of battery capacity. Current state-of-the-art noble metal catalysts achieves nearly 80% of the theoretical capacity. However, its cycling stability is severely limited to less than 200 cycles despite low discharge rate applied.Herein, we present a nitrogen plasma-enhanced copper sulfide/oxide catalyst (referred to as N-CuS) that exhibits good catalytic activity for its application as the air-breathing cathode for ZABs. The material is grown directly on metal foam surface using anodization, which is then treated using nitrogen plasma. Anodization creates defect-rich flakes of copper sulfide on the oxide surface, highly increasing surface area and creating the active sites. The material has good electrical conductivity and highly open porous structure that alleviates mass transport issues. Additionally, nitrogen plasma treatment further increases the surface area about 80%, and is expected to introduce nitrogen dopants to the surface, enhancing conductivity of the material. ECSA estimated by measuring Cdl shows that each process increases the ECSA by over 40 times and about 1.8 times, respectively.LSV of CuS and N-CuS half-cells have been performed to measure and compare catalytic performance of the material. N-CuS shows far higher current density and better catalytic activity (35mV less overpotential) than CuS, and higher output voltage is observed with N-CuS cells with the same current density. By assessing the GCPL (potential limited galvanostatic cycling) results, it was concluded that N-CuS requires lower charging voltage and exhibits higher discharge voltages than CuS.The overall performance was evaluated in a stack cell configuration, utilizing thin zinc foil as its anode to minimize mass error. The measured specific capacity of the cell was 789.3 mA·h·g-1, which approximately is 85% of the theoretical specific capacity of zinc-air cells (820 mA·h·g-1). This cell yields gravimetric energy density of about 666 Wh·kg-1. It is notable that these ZAB characteristics are comparable to Pt/C, the state-of-the-art catalyst as of now. N-CuS may be a viable replacement for the Pt/C electrode, resulting in the cost-saving effect. The cycling stability of both N-CuS and Pt/C-based ZAB has been assessed to show that N-CuS-based ZAB has much prolonged (more than twice the cycles) cyclability compared to Pt/C-based ZAB (Fig. S11).Additionally, ZAB constructed using N-CuS can operate in oxygen-deficient environments. As the counter reaction it utilizes redox reaction of copper oxides (Zn-Cu mode) in the substrate when operating in anaerobic conditions. The reduction of divalent and monovalent copper oxides appears as plateaus at 1.1 V and 0.8 V versus the zinc anode during GCPL. Due to this alternate reaction, the cell can operate even at low concentrations of oxygen or even in its absence.DFT calculations have been performed to elucidate the reaction mechanism and the intrinsic catalytic activity of the material, and shows nitrogen dopants improve reactivity of the active sites, thus reducing the overpotential.In summary, we have synthesized N-CuS as the OER/ORR catalyst for ZAB. Through anodization the catalyst was directly grown on the substrate and nitrogen plasma treatment further enhances the catalyst properties to render it higher surface area, conductivity, and better stability. This allows better reversibility in the OER/ORR and results in enhanced cyclability of the overall cell. The constructed RZAB exhibited high specific capacity of 789.3 mA·h·g-1, which, has higher capacity than the analogue using Pt/C catalyst. In addition, N-CuS based RZAB is capable of operating under oxygen-deficient conditions utilizing the metal oxide substrate. This allows the dual mode operation of zinc-air and zinc-copper modes, and results in a more consistent output from the RZAB, as short-term air supply issues could be buffered by this effect. Figure 1

Interface Engineering of Transition Metal-Based Heterostructure Electrocatalysts for Enhanced Hydrogen Evolution Reaction

Electrochemical water splitting to produce clean hydrogen plays a significant role in the development of the hydrogen economy. The rational design of highly efficient and inexpensive electrocatalysts is critical for improving water electrolysis efficiency. Herein, we report the fabrication of heterostructure monometallic, bimetallic, and trimetallic sulfides on Ni foam (NF) as porous self-supported electrodes for hydrogen evolution reaction (HER) via an energy-saving electrodeposition process. Molybdenum-cobalt-nickel sulfide electrode (MoCoNiS@NF) only requires a low overpotential of 114 mV to produce a current density of 10 mA cm-2 for HER, compared with nickel sulfides (NiS@NF, 142 mV) and cobalt-nickel sulfides (CoNiS@NF, 129 mV). The desirable HER performance of MoCoNiS@NF results from the synergistic effect of heterostructure interfaces of multi-metal sulfides, providing high intrinsic catalytic activity and a large amount of catalytic active sites. Electrochemical impedance spectroscopy and Tafel slope analysis proved the fast reaction kinetics of MoCoNiS@NF toward HER. Our present work provides valuable insights into the working mechanisms behind the HER catalytic process and new perspectives for the future design of cost-effective electrocatalysts for HER.

Carbon cloth supporting (CrMnFeCoCu)3O4 high entropy oxide as electrocatalyst for efficient oxygen evolution reactions

High-entropy oxides (HEOs) have received more attentions for the oxygen evolution reaction (OER) due to their rich active sites and high configurational entropy. However, the difficulty of electron transfer during the catalysis process limits the application of HEOs in OER catalysis. Herein, we proposed the carbon cloth (CC) supporting (CrMnFeCoCu)3O4 HEO with spinel structure synthesized by the hydrothermal method following with the calcination. The carbon cloth used as the support of HEO could improve the conductivity and stability of the catalyst. Meanwhile, the excellent catalytic activity of HEO with the synergistic effects of multiple metal elements would be maintained. And the homo-disperse HEO nanoparticles were exposed on the surface carbon fibers, which was conducive to contact with electrolyte. Based on the above merits, the intrinsic catalytic activity of (CrMnFeCoCu)3O4/CC was enhanced, which was attributed to the self-regulating electronic structure and the fine HEO nanoparticles exposed on the surface of catalysts. And the catalytic kinetic process of (CrMnFeCoCu)3O4/CC was accelerated, mainly due to its conductivity and richer oxygen vacancies. The (CrMnFeCoCu)3O4/CC exhibited the outstanding OER performance with an ultralow overpotential (210.8 mV @10 mA·cm−2), a smaller Tafel slope value (59.4 mV·dec−1), and super long-term durability, which was competitive with other transition metal oxides based catalysts and noble metal oxides. Therefore, the excellent OER performance implied that the (CrMnFeCoCu)3O4/CC is an OER catalyst candidate for practical application.

Novel Ni–Ru/CeO2 catalysts for low-temperature steam reforming of methane

Upgrading of biogas and biomethane into H2-rich streams by steam reforming is regarded as an effective strategy to reduce fossil fuel consumption contributing to the transition towards a green energy system. In this context, novel reactor configurations such as membrane reactors appear a promising route for process intensification, but they require novel catalysts more active at low temperatures, stable, and resistant to coke formation. In this work, we prepared and tested structured catalysts characterized by a low Ni content (7 wt%) and a very low Ru content (≤1 wt%) supported on ceria and deposed onto SiC monoliths. Catalysts were tested at low temperatures (<600 °C), i.e. at temperatures suitable for applications in Pd-based membrane reactors. Fresh and used catalysts were characterized by ICP-MS, N2 physisorption, XRD, TEM, SEM-EDS, XPS and H2-TPR to identify the physicochemical properties affecting the catalytic activity. The catalysts showed good activity towards methane reforming, stable performance, and good resistance to coke formation. Ruthenium affects both the intrinsic catalytic activity and the resistance to the inhibiting effect of steam on the reaction rate. This is related to improved redox properties due to the intimacy between the active metals and their strong-metal-support-interaction with the ceria. Finally, our catalysts show self-activation under reaction conditions, which is an interesting property for applications.

Reduction performance and degradation mechanism of chlorinated hydrocarbon electrocatalytic hydrodechlorination using synthetic Ti/Pd cathode

In this research, an orthogonal experiment (45) was conducted to explore the degradation of CT in Ti/Pd sealed cathode chamber, and electrochemical characteristics of electrodes were analyzed simultaneously, demonstrating its superior capability for the dechlorination of aqueous CT. The results showed there existed a suitable electrolytic condition for CT hydrodechlorination, when Na2SO4 concentration was 0.4 mg·L−1, current density was 12 mA·cm−2 and initial pH was 7 within 45 min electrolysis time, the 89.42 % of CT was degraded, and the complete vanishment of CT until 65 min occurred. SEM and EDS analysis were used to comprehensively characterize the Ti/Pd cathode. Besides, theoretical calculations showed that Pd modified cathode possesses excellent intrinsic catalytic activity. CV curves and K-L calculation elucidated the one-electron-transfer process underlying the stepwise dechlorination of chlorinated alkanes at the Ti/Pd electrode. Cl− index calculations verified that CT degradation was partial dechlorination. The scavenging activity test of atomic hydrogen (H⁎ads) proved the pivotal roles of H⁎ads in CT hydrodechlorination. The voltage control degradation pathway of CT was put forward, which aligned well with the kinetic model. Overall, the Ti/Pd cathode represents a promising electrode material with significant potential for CT degradation from aqueous solutions.

Single step grown porous polycrystalline nickel microstructures with ultra-thin defect rich surface oxide for alkaline water oxidation

Investigation on the intrinsic catalytic activity of structurally diverse polycrystalline nickel microstructures such as porous nickel sheets (PNS), porous folded/curled nickel structures (PFNS) and porous nickel balls (PNB) revealed the surface bounded electrocatalytic activities within an alkaline reaction environment for water oxidation. Nickel microstructures were grown via template/surfactant-free, single step solution combustion technique in air atmosphere. The distinct morphologies (porous nickel sheets, porous folded/curled nickel structures and porous nickel balls) were achieved through changing the quantity of HNO3 in the reaction mixture. The physicochemical characterisations were done with XRD, FESEM, EDS and XPS. Microscopic studies revealed the growth of nickel grains with numerous macro pores forming microstructures in distinct morphologies. The O ls spectra of XPS studies revealed the presence of O−/O2− sites and Ni 2p spectra were distinguished between the formation of Ni0/Ni2+/Ni3+ states, implied the existence of surface oxide with plenty of defects. The synergistic effect results from the formation of microscopic porous architectures with defect rich surface oxide on the electrochemical behaviour and OER activity of PNS, PFNS and PNB were discussed with electrochemical techniques such as CV, LSV, EIS and CP. The OER kinetics in terms of relatively low value of overpotential at 10 mA cm−2 and Tafel slope along with high specific activity of PNS/GCE with respect to PFNS/GCE and PNB/GCE were attributed to the combined effect of increase in electrochemical surface area, high roughness factor and fast charge transfer kinetics. The better electrochemical performance and OER activities of porous nickel sheets in comparison with folded/curled nickel structures and nickel balls is contributed to the unique 2D porous architecture with plenty of oxygen vacancies. This structure not only expose more surface for the formation of passive oxide layer in an alkaline reaction environment but also exhibit facile charge transport properties, causes the generation of numerous surface-active sites for electrocatalytic water oxidation. The outcome of our work gives new insights on the surface electrochemistry of polycrystalline nickel, enables micro-structuring as a prospective strategy towards the optimization of electrocatalysts as anode material for alkaline water oxidation.