Platinum-based Electrocatalysts Research Articles

Activity of Platinum-Based Cathode Electrocatalysts in Oxygen Redaction for Proton-Exchange Membrane Fuel Cells: Influence of the Ionomer Content

Studying the ORR activity of platinum-based electrocatalysts is an urgent task in the development of materials for proton-exchange membrane fuel cells. The catalytic ink composition and the formation technique of a thin layer at the RDE play a significant role in studying ORR activity. The use of a polymer ionomer in the catalytic ink provides viscosity as well as proton conductivity. Nafion is widely used as an ionomer for research both at the RDE and in the MEA. The search for ionomers is a priority task in the development of the MEA components to replace Nafion. The study also considers the possibility of using the LF4-SK polymer as an alternative ionomer. The comparative results on the composition and techniques of applying the catalytic layer using LF4-SK and Nafion ionomers are presented, and the influence of the catalytic ink composition on the electrochemical characteristics of commercial platinum–carbon catalysts and a highly efficient platinum catalyst based on an N-doped carbon support is assessed.

Highly dispersed ultrafine PtCo alloy nanoparticles on unique composite carbon supports for proton exchange membrane fuel cells.

The design of highly efficient and robust platinum-based electrocatalysts is pivotal for proton exchange membrane fuel cells (PEMFC). One of the long-standing issues for PEMFC is the rapid deactivation of the catalyst under working conditions. Here, we report a simple synthesis strategy for ultrafine PtCo alloy nanoparticles loaded on a unique carbon support derived from a zeolitic imidazolate framework-67 (ZIF-67) and Ketjen Black (KB) composite, exhibiting a remarkable catalytic performance toward the oxygen reduction reaction (ORR) and PEMFC. Benefitting from the N-doping and wide pore size distribution of the composite carbon supports, the growth of PtCo nanoparticles can be evenly restricted, leading to a uniform distribution. The Pt-integrated catalyst delivers an outstanding electrochemical performance with a mass activity that is 8.6 times higher than that of the commercial Pt/C catalyst. Impressively, the accelerated durability test (ADT) demonstrates that the hybrid carbon support can significantly enhance the durability. Theoretical simulations highlight the synergistic contribution between the supports and the PtCo nanoparticles. Moreover, hydrogen-oxygen fuel cells assembled with the catalyst exhibited a high power density of 1.83 W cm-2 at 4 A cm-2. These results provide a new opportunity to design advanced catalysts for PEMFC.

First-principles studies of enhanced oxygen reduction reactions on graphene- and nitrogen-doped graphene-coated platinum surfaces.

Developing innovative platinum-based electrocatalysts and enhancing their efficiency are crucial for advancing high-performance fuel cell technology. In this study, we employed DFT calculations to provide a theoretical basis for interpreting the impact of graphene coatings on various Pt surfaces on oxygen reduction reaction (ORR) catalytic activity, which are currently applied as protective layers in experiments. We comprehensively assess the geometric and electronic properties of Pt(100), Pt(110), and Pt(111) surfaces in comparison to their graphene-coated counterparts, revealing different adsorption behaviors of O2 across these surfaces. The ORR mechanisms on different Pt surfaces show distinct rate-determining steps, with Pt(111) showing the highest ORR activity, followed by Pt(110) and Pt(100). Graphene coatings play a key role in enhancing charge transfer from the surface, resulting in modifications of O2 adsorption. Despite influencing ORR kinetics, these graphene-coated surfaces demonstrate competitive catalytic activity compared to their bare counterparts. Notably, Pt(111) with a graphene coating exhibits the lowest activation energy among graphene-coated surfaces. Our calculations also suggest that the ORR can occur directly on non-defective Pt@graphene surfaces rather than being restricted to exposed Pt centers due to point defects on graphene. Furthermore, our work highlights the potential of nitrogen doping onto the Pt(111)@C surface to further enhance ORR activity. This finding positions nitrogen-doped Pt@C as a promising electrocatalyst for advancing electrochemical technologies.

Well-organized metal-free chemically reduced graphene oxide sheets as electrocatalysts for enhanced oxygen reduction reactions in alkaline media

Metal-free reduced graphene oxides have recently received attention as potential replacements for platinum-based electrocatalysts. In the present study, we investigated the electrochemical characteristics of chemically reduced graphene oxides (C-rGO) in oxygen reduction reactions (ORR). The C-rGO displays significantly enhanced catalytic activity towards the ORR in alkaline solutions compared to the starting graphene oxide (GO). The thermal properties of C-rGO show good thermal stability, and structural defects in C-rGO were confirmed by Raman analysis. Electrochemical impedance spectroscopy (ESI) analysis confirmed C-rGO superior electron transport capacity over GO. The onset potential (0.82 V), lower Tafel slope, and current density (-5.6 × 10-4 mA/cm2) of the C-rGO catalysts were increased compared to GO due to the majority of functional groups removed after chemical reductions. It's clear that catalysts work through four electron (e-) ORR processes bacause the C-rGO has higher electron transfer numbers (3.8 at a potential of −0.63 V).

Accelerated stress tests for Pt/C electrocatalysts: An approach to understanding the degradation mechanisms

The degradation of the nanostructured platinum-based electrocatalysts during their operation poses a major problem for the performance and durability of PEMFCs and devices based on them. Therefore, the methodological aspects of research related to the quantitative assessment of the materials’ degradation as well as the mechanism of the processes causing it are gaining increasing attention. The degradation processes of the same Pt/C catalyst containing the nanoparticles of similar size uniformly distributed over the surface of the carbon support were studied using eight relevant protocols of the accelerated stress testing. Special attention was paid to electron microscopy examination of the catalyst’s microstructure before and after stress tests as well as to determination of the electrochemically active surface area and the activity of the catalyst in the ORR after the stress testing. We also studied the influence of the atmosphere, in which testing was performed, as well as the effect of the electrode rotation on the degradation rate. The results of the study carried out demonstrate the features of the catalyst’s degradation in different modes and facilitate the choice of optimal protocols and stress testing conditions.

Assessing the catalytic performance of Cu@Ln (Eu, Sm)-N-C composites as bifunctional electrocatalysts using mesoporous silica-protected calcination

Synthesis of a composite with high technical performance and low cost instead of Platinum-based electrocatalysts has become an investigation hotspot to develop fuel cells and storage technologies. So, in the current investigation, three new bifunctional electrocatalysts incorporating lanthanides into Zeolitic Imidazolate Framework (ZIF)-8 are fabricated and assessed. First, by using a facile protocol, three trimetallic composites consisting of Europium (Eu), Samarium (Sm), Copper (Cu), and ZIF-8 are prepared, and the fabricated samples are labeled as EuCu-ZIF, SmCu-ZIF, and SmEuCu-ZIF. Next, in order to eliminate the irreversible fusion and quick aggregation of metal nanoparticles through the high-temperature carbonization process, the mesoporous-silica-protected calcination technique is investigated. After the Hydrofluoric (HF) etching process, the Cu@Ln (Eu, Sm)-N-C electrocatalysts are formed. Based on the fabricated samples, the Cu@Eu-N-C electrocatalyst exhibited the best Oxygen Reduction Reaction (ORR) performance with an onset potential of −0.06 V vs Ag/AgCl. Additionally, the electron transfer number for this composite is found to be 3.68. The GCD experiments show that the Cu@Eu-N-C electrode has the greatest specific capacitance, measuring 431 F g−1 when tested at 1 A g−1. It is deduced that the introduction of Eu3+ and Sm3+ as metal ions in the ZIF-8 catalyst led to an improvement in defects in the carbon matrix and mass transfer, illustrating the fabricated catalysts have an acceptable efficiency for ORR and storage applications. Indeed, due to the use of metallic ions (Ln and Cu), highly effective active sites were formed, resulting in an outstanding improvement in ORR efficiency. Also, it was found that with the use of mesoporous-silica protection for the fabricated samples, there is a remarkable improvement in the onset potential and specific capacitance parameters.

Zn-Induced Synthesis of Porous Fe-N,S-C Electrocatalyst with Iron-Based Active Sites Containing Sulfides, Oxides and Nitrides for Efficient Oxygen Reduction and Zinc-Air Batteries.

There is an urgent need to design and synthesize non-noble metal electrocatalysts (NNMEs) for the replacement of platinum-based electrocatalysts to enhance the sluggish oxygen reduction reaction (ORR) for Zn-air batteries and fuel cells. Herein, Fe-N,S-C materials were fabricated through two steps: first, reprecipitating hemin by adjusting the pH and, then, decorating it with melamine and cysteine in the presence of Zn2+. The resulting Fe-N,S-C-950 (Zn) was prepared after pyrolysis at 950 °C. Using this method, abundant iron-based active species with good dispersion were obtained. The fabrication of more micropores in Fe-N,S-C-950 (Zn) plays a positive role in the improvement of ORR activity. On comparison, Fe-N,S-C-950 (Zn) outperforms Fe-N,S-C-950 and Fe-N-C-950 (Zn) with respect to the ORR due to its larger specific surface area, porous structure, multiple iron-based active sites and N- and S-doped C. Fe-N,S-C-950 (Zn) achieves outstanding ORR performances, including a half-wave potential (E1/2) of 0.844 V and 0.715 V versus a reversible hydrogen electrode (RHE) in 0.1 M KOH and 0.1 M HClO4 solution, respectively. In addition, Fe-N,S-C-950 (Zn) shows an outstanding Zn-air battery performance with an open-circuit voltage (OCV) of 1.450 V and a peak power density of 121.9 mW cm-2, which is higher than that of 20 wt% Pt/C. As a result, the as-prepared electrocatalyst in this work shows the development of the Zn-assisted strategy combined with the assembly of porphyrins as NNMEs for the enhancement of the ORR in both alkaline and acidic solutions.

Defect Engineering of a High-Entropy Metallic Glass Surface for High-Performance Overall Water Splitting at Ampere-Level Current Densities.

Platinum-based electrocatalysts possess high water electrolysis activity and are essential components for hydrogen evolution reaction (HER). A major challenge, however, is how to break the cost-efficiency trade-off. Here, a novel defect engineering strategy is presented to construct a nanoporous (FeCoNiB0.75 )97 Pt3 (atomic %) high-entropy metallic glass (HEMG) with a nanocrystalline surface structure that contains large amounts of lattice distortion and stacking faults to achieve excellent electrocatalytic performance using only 3at% of Pt. The defect-rich HEMG achieves ultralow overpotentials at ampere-level current density of 1000mAcm-2 for HER (104mV) and oxygen evolution reaction (301mV) under alkaline conditions, while retains a long-term durability exceeding 200h at 100mAcm-2 . Moreover, it only requires 81 and 122mV to drive the current densities of 1000 and 100mAcm-2 for HER under acidic and neutral conditions, respectively. Modelling results reveal that lattice distortion and stacking fault defects help to optimize atomic configuration and modulate electronic interaction, while the surface nanoporous architecture provides abundant active sites, thus synergistically contributing to the reduced energy barrier for water electrolysis. This defect engineering approach combined with a HEMG design strategy is expected to be widely applicable for development of high-performance alloy catalysts.

Highly durable graphene-encapsulated platinum-based electrocatalyst for oxygen reduction reactions synthesized by solution plasma process

Though expensive platinum (Pt) is used as catalyst for oxygen reduction reaction (ORR) in polymer electrolyte fuel cells (PEFCs), insufficient durability remains as a bottleneck for commercialization of PEFCs. Improving both catalytic performance and durability by graphene encapsulation is an attractive strategy to solve this problem. In this study, graphene-encapsulated PtFe core-shell catalyst is synthesized with dimethyl formamide (DMF) and a pair of Pt and Fe electrodes without using any metal salts by utilizing the solution plasma (SP) process. TEM and EELS results show synthesized PtFe nanoparticles are encapsulated with close to single-layered highly crystallized graphene. Although commercial Pt/C showed significant performance degradation (ECSA −33%, MA −68%) after 50,000 cycles of accelerated durability test (ADT), PtFe core-shell catalyst shows remarkably improved durability (ECSA −13%, MA −19%) while graphene shell clearly remains. The improved durability is more prominent in the single cell test, the decrease in maximum power density after 6000 cycles of ADT was significantly lower as −1.2%, compared to that of Pt/C (−52.1%). This study introduces a novel and attractive catalyst synthesis process by the SP method followed by heat treatments and suggests graphene encapsulation can improve long-term durability of catalyst while maintaining ORR activity.

Engineering single-atom Fe–N active sites on hollow carbon spheres for oxygen reduction reaction

Seeking alternatives to noble metals-based electrocatalysts for oxygen reduction reaction (ORR), hollow carbon spheres (CSs) were finely tuned with stable single-atom Fe–N species through a synthesis methodology requiring only earth-abundant metal precursors. CSs with different sizes were synthesized by sol-gel polycondensation of resorcinol with formaldehyde over silica nanoparticles, followed by thermal annealing and silica etching. A catalyst screening revealed the positive impact of both the hollow core and structural defects of the CSs for ORR. Single-atom Fe–N active sites were introduced on the best performing CSs through simultaneous incorporation of iron and nitrogen precursors, and glucose. A significant enhancement in ORR activity was observed despite the small iron load introduced (0.12 wt%). ORR performance indicators, advanced characterization, and molecular simulation studies revealed nitrogen's crucial role in anchoring individual iron atoms and modulating the charge density nearby the active sites (increase of 80 mV in the half-wave potential). Adding glucose as a chelating agent enhances the metal-heteroatom coordination and subsequent dispersion of iron, accounting for an increase of 20 mV in the half-wave potential, an average of electrons transferred as high as 3.9 (at 0.4 V vs. RHE), and higher stability (99%) than that of a platinum-based (20 wt%) electrocatalyst (92%).

Microbial synthesis of N, P co-doped carbon supported PtCu catalysts for oxygen reduction reaction

Developing highly efficient and stable platinum-based electrocatalyst for oxygen reduction reaction (ORR) is critical to expediting commercialization of fuel cells. Herein, several PtCu alloy nanocatalysts supported on N, P co-doped carbon (PtCu/NPC) were prepared by microbial-sorption and carbonization-reduction. Among them, PtCu/NPC-700 °C exhibits excellent catalytic performance for ORR with a mass activity of 0.895 A mgPt−1 (@0.9 V) which is 8.29 folds of commercial Pt/C. Additionally, the ECSA and MA of PtCu/NPC-700 °C only decrease by 14.2% and 18.7% respectively, while Pt/C decreases by 35.2% and 52.8% after 10,000 cycles of ADT test. Moreover, the PtCu/NPC-700 °C catalyst emanates a maximum power density of 715 mW cm−2 and only 11.1% loss of maximum power density after 10,000 ADTs in single-cell test, indicating PtCu/NPC-700 °C also manifests higher activity and durability in actual single-cell operation than Pt/C. This research provides an easy and novel strategy for developing highly active and durable Pt-based alloy catalyst.

Electronic and Coordination Effect of PtPd Nanoflower Alloys for the Methanol Electrooxidation Reaction

Platinum-based electrocatalysts usually exhibit limited and quickly vanished activity for the methanol oxidation reaction (MOR) due to active site occupation and surface intermediate poisoning, especially CO. The attendant synergistic effect of the alloy strategy is often executed to improve these flaws. Here, PtPd nanoflower alloys uniformly anchored on the carbon paper were successfully synthesized by electrodeposition to construct well-defined active sites, over which high MOR activity and tolerance were realized. The homogeneous alloy structure of PtPd nanoflowers was confirmed by TEM and XAFS. Impressively, the Pt1Pd1-N NFs/CP exhibited an excellent mass activity of 9.25 A mgPt+Pd–1 and specific activity of 13.2 mA cmECSA–2 of MOR in the alkaline electrolyte, and 87.8% of the initial activity was still retained after 500 cycles. In situ infrared spectroscopy revealed that Pt1Pd1-N NFs/CP ensured the complete oxidation of methanol following a CO-free path. The investigation of the electronic and coordination structure demonstrated that the Pt–Pd adjacent sites with a zero valence are the highly active center for MOR, and the synergistic effect between Pt and Pd greatly improved the MOR electrocatalytic performance. This work offers an effective strategy to precisely control the number and structure of decorating species for constructing alloy nanocatalysts to enhance the electroactivity toward MOR.

Frustrating Surface Segregation by Nanoconfinement: Boosting Electrochemical Ozone Production over a B13C2-Encapsulated PtNi Alloy Electrocatalyst

A major challenge that limits the applications of nanostructured electrocatalysts is precise surface structure regulation. The critical performance-impeding factors for the important electrochemical ozone production (EOP) lie in the leaching-induced poor stability as well as the competing oxygen evolution and ozone production reactions over the most promising platinum-based electrocatalysts. Although composition diversification by alloying appears to be a prevailing strategy to optimize platinum-based electrocatalysts, a practical restriction turns out to be the inevitable surface segregation and termination of platinum-enriched structures due to their lower surface energies. In this work, we introduce the nanoconfinement of intermetallic platinum–nickel nanostructures encapsulated by boron carbide, which effectively frustrates the surface segregation of alloy nanostructures and well maintains the pristine termination of the alloy. Precise atomic-level structural elucidation and model construction of the encapsulated alloy nanostructures are achieved by quantitative electron microscopy. The composite nanoalloy with a unique surface termination evokes synergetic catalytic effects that promote the charge transfer between the surface and adsorbed oxygen intermediates, which entails outstanding EOP performance with a high Faraday efficiency of 14.8% in neutral media and long-term stability of up to 120 h as a qualified electrocatalyst for the EOP electrolyzer devices. More importantly, the current work paves a new route to overwhelm the thermodynamically limited surface structures of bare nanoalloy catalysts through diverse nanoconfinement strategies.

Conductive Ytterbium Metal–Organic Framework Composite: A Lanthanide-Based Complex ORR Catalyst

Extensive research work has been invested in the past decade in finding replacements for platinum-based electrocatalysts for the oxygen reduction reaction in fuel cells. The majority of these alternative electrocatalysts are based on transition-metal ions coordinated by organic ligands. Different from previously reported approaches for electrocatalysts, we describe here the synthesis, characterization, and oxygen reduction reaction activity of lanthanide complex electrocatalyst with ytterbium as the metal center. A metal–organic framework of Yb and benzene tricarboxylic acid as a ligand was synthesized on activated carbon (Yb(III)BTC@AC) to achieve electrical conductivity in a procedure similar to M-BTC@AC electrocatalysts with transition-metal centers. The Yb complex in activated carbon presents oxygen reduction reaction activity in alkaline solution with high onset potential relative to other nonpyrolyzed molecular electrocatalysts and proceeds mostly through the preferred four-electron reduction mechanism. This work presents a novel category of platinum group metal-free electrocatalysts as an alternative electrocatalyst for the oxygen reduction reaction.

Rare-earth modified platinum-based electrocatalysts incorporating anodic glycerol oxidation reactions while promoting cathodic hydrogen evolution reactions

Glycerol electrooxidation (GOR) is a safe and clean method for conversion of glycerol. In the course of this work, a series of PtxCe/C catalysts have been synthesized by successive polyol reduction methods as well as etching and calcination. Various physicochemical characterrisation and electrochemical measurements have demonstrated the excellent performance of Pt3Ce/C composites in glycerol oxidation (GOR) and hydrogen evolution reactions (HER). The Pt3Ce/C catalyst showed better performance in GOR and HER compared to commercially available Pt/C electrocatalysts. This paper demonstrates an energy efficient electrocatalyst for the simultaneous precipitation of hydrogen from glycerol oxidation.

Recent progress in the development of Platinum-based electrocatalysts for the oxidation of ethanol in fuel cells

Humans have an ever-increasing and ever-insatiable need for energy. The world's energy demands are currently being met by burning nonrenewable fossil fuels. Recurring challenges for civilization include developing dynamic energy cradles for a prosperous society to lessen fossil fuel depletion and environmental issues. The energy gap in the modern era can only be closed by the discovery of vast quantities of non-conventional resources. In place of dirty and inefficient fossil fuels, fuel cells provide a powerful and environmentally friendly alternative. In the realm of fuel cells, the direct ethanol fuel cell (DEFC) has garnered a lot of attention because it is a renewable fuel, easy to handle, and safe to use. High catalytic capabilities and durability make Pt-based electrocatalysts very promising. However, widespread commercial use has been hampered by their expensive price, poor stability, and Pt shortage. The keys to DEFC's practical uses are increasing the activity and durability of Pt-based electrocatalysts while decreasing the Pt content. This article will provide a summary of the most recent results about the development of Pt-based alloy electrocatalysts for ethanol oxidation. In addition, the most significant technological challenges are recognized, as well as prospective future study fields to solve these difficulties in order to pave the way for more research and development leading to practical implementation.

Direct Use of 3d-Transition Metal Organic Framework as Catalyst for Oxygen Evolving Reaction (OER) and Hydrogen Evolving Reaction (HER)

High-purity hydrogen can be produced using an effective process known as electrochemical water splitting to provide environmentally acceptable fuels. The advancement of affordable, earth-rich catalysts is the fundamental obstacle to electrochemical water splitting’s wide-scale industrial applications. Oxygen evolving reactions (OERs) and hydrogen evolving reactions (HERs) are two of the processes involved in electrochemical water splitting. Widespread interest has been shown in creating efficient first-row transition metal electrocatalysts that can take the role of platinum-based electrocatalysts for both oxygen and hydrogen evolving reactions. A family of crystalline porous materials made from organic ligands and metal ions are known as metal organic frameworks (MOFs). A promising family of novel materials called MOFs has been developed for high-efficiency OER and HER electrocatalysts. Direct MOF catalysts and MOF-derived catalysts are the two divisions of MOF-based catalysts. The following are examples of MOF-derived catalysts: (i) guest@ MOF composites; (ii) hybrid materials produced by pyrolyzing MOFs; and (iii) hybrid materials created from MOFs. The best direct catalysts for OER and HER are reportedly nickel/cobalt monometallic MOF and iron-nickel/iron-cobalt heterometallic MOF. According to one theory, the breakdown of organic ligands and the formation of molecules based on water-oxidizing oxides may be a result of first-row transition MOFs being exposed to the hostile HER and OER conditions. The most recent advancements in first-row transition MOFs as direct catalysts of OER and HER are outlined in this article.

Enhanced Electrocatalytic Activity for Hydrogen Evolution Reaction from Electrophoretically-Deposited BiSbSe3 Nanoparticles

For the development of renewable energy conversion and storage systems, it is vital to investigate earth-abundant, noble-metal-free, and highly efficient electrocatalysts for the hydrogen evolution process (HER). Platinum and other precious metals-based electrocatalysts show better HER activity in acidic conditions than other electrocatalysts due to their fast kinetics and lower Tafel slope.[1] However, because they are rare and costly, they are challenging to deploy in practical applications. As a result, there has been an ongoing search for low-cost and earth-abundant materials that may be used as an efficient alternative for platinum-based electrocatalysts, with the goal of developing more cost-effective and inexpensive H2 manufacturing processes. The layered 2D nanomaterials have sparked a lot of scientific attention because of their tremendous potential for both fundamental and practical investigations. Natural minerals of the group V-VI (V = Bi, Sb; VI = S, Se) have exceptional optical and electrical characteristics.[2] Because of their availability, low cost, and tunable characteristics, antimony/bismuth-based chalcogenides are garnering a lot of attention as potential candidates as electrocatalysts for acidic HER. We have shown an efficient and straightforward approach for the electrochemical exfoliation of BiSbSe3 nanostructures from the ball-milled BiSbSe3 sample; the process parameters were adjusted in terms of time and applied voltage. Furthermore, a simple and straightforward electrophoretic deposition process was used to synthesize BiSbSe3 nanoparticles from exfoliated BiSbSe3 nanostructures. A DC voltage was supplied between the two inert electrodes in an aqueous electrolyte for the electrophoretic deposition of BiSbSe3 nanostructures directly onto a gold substrate. Charged particles or sheets suspended in the electrolyte are activated to migrate toward the electrode and deposit when a voltage is applied. The BiSbSe3 nanoparticles were deposited onto the positive electrode because the exfoliated BiSbSe3 nanostructures in water had a negative zeta potential. BiSbSe3 nanostructures prepared through electrochemical exfoliation method are electrophoretically deposited onto the gold substrate to obtain BiSbSe3 nanoparticles, were investigated as active electrocatalysts for HER in 0.5 M H2SO4 solution using a three-electrode set up. The optimized BiSbSe3 catalyst (10V10M-Au-7.5) is identified as highly active HER activity, having a low overpotential of 72 mV @ 10 mA cm−2 and a low Tafel slope of 31.6 mV dec-1, which far better than the antimony/bismuth chalcogenide system and very close to the state-of-the-art Pt/C catalyst. We demonstrate that the electrocatalytic HER activity is enhanced by highly active edge sites, large available surface active sites, defects created and partial oxidization of material during electrodeposition, and a synergistic effect between BiSbSe3 and the substrate.

Carbon dots modified molybdenum disulfide as a high-efficiency hydrogen evolution electrocatalyst

Molybdenum disulfide (MoS2) is considered a low-cost material that may replace platinum-based electrocatalysts towards hydrogen evolution reaction (HER). However, the catalytic activity of MoS2 is limited by the low conductivity and lack of active sites. Here, a biomass carbon dots-molybdenum disulfide (BCDs-MoS2) composite was synthesized as a HER catalyst by a simple hydrothermal method. The BCDs-MoS2 catalyst displayed excellent electrocatalytic performance for HER with lower onset overpotential (115 mV), smaller Tafel slope (56.57 mV dec−1) as well as high cycling stability, which superior to those of homemade MoS2, commercial MoS2, and most of the reported MoS2-based catalysts. According to the characterization results of morphology, surface properties, and valence states of elements, the outstanding catalytic activity of BCDs-MoS2 is ascribed to its loose structure with a large specific surface area along with abundant edges and defects, and the increase in the amount of S22− and S2− which possess higher activity due to the addition of the BCDs. This study can afford a new strategy to design high performance HER catalysts.

Engineered interfaces of WSe2/rhenium doped SnSe2 heterostructures nanosheet arrays for superior hydrogen generation and flexible supercapacitor

Two-dimensional hybrid heterostructures offer substantial benefits in electrochemical energy storage and conversion due to their unique compositional and structural features. It is a low-cost alternative to widely used platinum-based electrocatalysts for the commercialization approach. However, making heterostructures with other semiconductor materials bound together by van der Waals or covalent interactions is practically challenging. Here we report a hybrid electrocatalyst prepared by the hydrothermal growth of WSe2 nanosheet arrays decorated by rhenium (Re)-doped tin diselenide (SnSe2) (WSe2@ReSnSe2). The vertically aligned high-density arrays expose more active sites and promote the charge/ion transfer due to the open porous space inside the array of hybrid heterostructure composite. Moreover, the Re doping improves the electron transfer by shifting Fermi level and also provides an active site to enhance catalytic activity. As demonstrated, WSe2@ReSnSe2 hybrid heterostructure exhibits excellent and stable catalytic activity for hydrogen evolution with the overpotential and Tafel slope of 193 mV and 66 mV/dec in acidic medium. The fabricated flexible supercapacitor based on a hybrid heterostructure catalyst achieves the specific capacitance (Csp) of 175 F/g at a current density of 1 A/g with Csp retention rate of 84.6% after the 5,000 cycles at 10 A/g.