Tafel Slope Value Research Articles

Novel synthesis of CuHCF/B-rGO composites for oxygen evolution reaction activity

In this work, we have focused on the preparation of copper hexacyanoferrate/boron doped rGO composites (abbreviated as CuHCF/B-rGO) by employing simple co-precipitation technique subsequently processed with ultrasonication method. The XRD spectra confirmed the existence of the cubic structure of copper hexacyanoferrate with high crystalline peaks. The prepared nanocomposite morphology was evaluated by scanning electron microscopy (SEM), and confirmed CuHCF nanoparticles formation with flake-like and wrinkled sheets. Pure CuHCF nanostructures revealed good OER action at 430 mV to obtain 10 mA/cm2. The obtained CuHCF product OER activity can be further upgraded by incorporating the electrically conductive boron doped reduced graphene oxide matrix into CuHCF nanostructures, for the reason that the overpotential of the CuHCF/B-rGO was reduced to 380 mV to attain 10 mA/cm2 with 88 mV/dec Tafel slope value. The doping of heteroatom considerably improves charge-transfer resistance of metal hexacyanoferrate, giving a small resistance value of 2.97 Ω, which was lower than that of CuHCF (5.57 Ω) and CuHCF/rGO (4.31 Ω). Furthermore, the catalytic activity of the CuHCF/B-rGO was stable at prolonged hours with a small decay of 12.5%. Therefore, this work offers new approach to stimulate the catalytic performance of metal hexcyanoferrate by highly conductive carbon-based materials for water splitting performance.

Exploring pyrolusite β-MnO2 as a robust support for noble metal catalysts in proton exchange membrane water electrolysis

Proton exchange membrane water electrolysis (PEMWE) represents a promising avenue for producing hydrogen sustainably. Nonetheless, its widespread adoption encounters hurdles owing to the sluggishness of the oxygen evolution reaction (OER) and the expensive noble metal catalysts, particularly iridium (Ir). Our investigation addresses these challenges by examining pyrolusite β-MnO2 as a robust substrate for noble metal catalysts, including iridium (Ir) and ruthenium (Ru), within PEMWE systems. We illustrate that nanostructured β-MnO2 effectively supports Ir and Ru catalysts, resulting in significantly improved catalytic activity for acidic OER compared to conventional IrO2 catalysts. The morphology shows nanorod structures with thicknesses ranging of 30–60 nm. The catalytic activity exhibits a lower overpotential of 215 mV and a higher Ir mass activity of 2268.7 A·gIr−1. The catalyst also exhibits lower Tafel slope value (37.82 mV/dec) and higher reaction kinetics. The catalyst also shows durability for the 12h under corrosive acidic OER conditions. The enhancements in performance can be attributed to the distinctive nanostructure of the Mn1-xTixO2 (MTO) support, which facilitates the even distribution of Ir and Ru catalysts. Additionally, the incorporation of titanium in pyrolusite β-MnO2 enhances the electrochemical durability of the MTO support under challenging acidic OER conditions.

Interface Engineering Induced by Low Ru Doping in Ni/Co@NC Derived from Ni-ZIF-67 for Enhanced Electrocatalytic Overall Water Splitting.

Electrochemical water splitting is a promising approach for hydrogen evolution reactions (HER); however, the oxygen evolution reaction (OER) remains a major bottleneck due to its high energy requirements. High-performance electrocatalysts capable of facilitating HER, OER, and overall water splitting (OWS) are highly needed to improve OER kinetics. In this work, we synthesized a trimetallic heterostructure of Ru, Ni, and Co incorporated into N-doped carbon (denoted as Ru/Ni/Co@NC) by first synthesizing Ni/Co@NC from Ni-ZIF-67 polyhedrons via high-temperature carbonization, followed by Ru doping using the galvanic replacement method. Benefiting from increased active surface sites, modulated electronic structure, and enhanced interfacial synergistic effects, Ru/Ni/Co@NC exhibited exceptional electrocatalytic performance for both HER and OER processes. The optimized Ru/Ni/Co@NC catalyst, with a minimal Ru mass ratio of ∼2.07%, demonstrated significantly low overpotential values of 34 mV for HER and 174 mV for OER at a current density of 10 mA/cm2 with corresponding Tafel slope values of 33.42 and 34.39 mV/dec, respectively. Further, the optimized catalyst was loaded onto carbon paper and used as anode and cathode materials for alkaline water splitting. Interestingly, a low cell voltage of just 1.44 V was obtained. The enhanced electrolytic performance was further elaborated by density functional theory (DFT) calculations, which confirmed that Ru doping in Ni/Co introduced additional active sites for H*, enhancing adsorption/desorption abilities for HER (ΔGH* = -0.30 eV), lowering water dissociation barrier (ΔGb = 0.49 eV) and reducing the energy barrier for the rate-determining step of OER (O* → OOH*) to 1.62 eV in an alkaline environment. These findings reflect the significant potential of ZIF-67-based catalysts in energy conversion and storage applications.

Unlocking the Electrocatalytic Behavior of Cu2MnS2 Nanoflake-Anchored rGO for the Oxygen Evolution Reaction in an Alkaline Medium.

A catalyst of the oxygen evolution reaction (OER) that is viable, affordable, and active for effective water-splitting applications is critical. A variety of electrocatalysts have been discovered to replace noble metal-based catalysts. Of these, transition metal-based sulfides are essential for incorporating carbonaceous materials to improve electrical conductivity, resulting in better electrocatalytic performance. Our study illustrates the synthesis of Cu2MnS2 (CMS) nanoflakes and their different rGO composites (10 to 40 wt %) via a hydrothermal technique for an effective water oxidation reaction. The X-ray diffraction pattern reveals that the prepared Cu2MnS2 nanoflakes exhibit a cubic crystal structure. The high-resolution scanning electron microscopy and the high resolution transmission electron microscopy images corroborate the formation of the nanoflake-like morphology of Cu2MnS2 with the strong interaction of rGO. The selected area electron diffraction analysis pattern reveals a polycrystalline nature. The Fourier transform infrared spectrum shows the existence of a metal sulfur vibrational band at 590 cm-1, and Raman analysis infers the presence of rGO. The X-ray photoelectron spectroscopy spectra reveal the oxidation states of the elements present in the samples. Using Brunauer-Emmett-Teller analysis, the surface area of CMS-20 is found to be 117.04 m2/g. The measured OER overpotentials using linear sweep volammetry and the values are 380, 370, 340, 376, and 400 mV at 10 mA/cm2 for CMS, CMS-10, CMS-20, CMS-30, and CMS-40, respectively, and the corresponding Tafel slope values are 179, 158, 149, 206, and 240 mV/decade, respectively. The electrochemical active surface area is estimated using cyclic voltammetry for all of the catalysts, where CMS-20 showed a larger surface area. Also, the same catalyst exhibits good stability for ∼24 h at a constant potential, which is confirmed via chronoamperometry. Thus, combining transition metal-based sulfides with carbonaceous materials indicates improved catalytic behavior for the preparation of high-performance OER electrocatalysts. Overall, the prepared CMS-20 performed as an efficient OER electrocatalyst and can be utilized for practical applications in energy conversion.

Enhanced electrocatalytic CO2 reduction into formate: Unleashing the effect of engineered bimetallic oxides supported on activated carbon

The excessive concentration of anthropogenic CO2 continuously harms the atmosphere. Consequently, deploying CO2 via the electrochemical reduction approach has become a highly sought-after research thrust area. In this study, a facile, one-pot solution combustion synthesis method (SCSM) was employed for the synthesis of various mixed-metal oxides supported on porous activated carbon (SnO2-CuO@AC). The prepared materials are characterized by analytical and spectroscopic techniques. Electrochemical studies were performed for the SnO2-CuO@AC catalyst to reduce CO2 into formic acid via an electrochemical approach. The in-depth properties of the designed catalysts were analysed by theoretical calculations using FT-IR and XRD data. The SnO2-CuO@AC exhibited improved electrochemical performance with a high current density of −10.77 mAcm−2, a low overpotential of −1.29 V, a lower Tafel slope value of 100 mV/dec. The faradaic efficiency for formic acid was 78.8 % at 1.3 V vs. RHE, with high stability for 9 h. The presence of coordinated active sites and oxygen vacancies, and a lower Tafel slope, also endorses CO2 adsorption and activation, faster electron transfer and boosts CO2 reduction. The significant reactivity toward CO2 reduction is attributed to the intensity of interaction between CO2∗- and the electrocatalyst, followed by kinetic activation toward protonation to obtain the desired product.

Phosphorus doping heterostructure La(OH)3@CuO @NF as an advanced electrocatalyst for the oxygen evolution reaction

Due to the prevailing energy shortages, the pursuit of new alternative energy sources is becoming increasingly urgent. Hydrogen production through water electrolysis has emerged as a crucial method. However, the sluggish four-electron reaction in the oxygen evolution reaction (OER) remains the primary rate-limiting step. In this study, we synthesized a heterostructure La(OH)3@CuO-P material on the nickel foam (NF) substrate. The experimental results demonstrate that after phosphating treatment, the heterostructure La(OH)3@CuO-P exhibits exceptional catalytic performance with only 215 mV overpotential, a Tafel slope value of 79.36 mV/dec, and a bilayer capacitance of 39.02 mF/cm2 at a current density of 10 mA/cm2 for OER in a 1 M KOH solution. These values are significantly superior compared to those obtained using heterostructure La(OH)3@CuO alone which showed an overpotential value of 365 mV at a current density of 10 mA/cm2. Moreover, during cyclic voltammetry testing for up to 500 cycles, La(OH)3@CuO-P also demonstrates relatively stable performance. Analyses suggest that composite heterostructure effectively addresses issues such as insufficient conductivity of La(OH)3 and monomer aggregation tendency for CuO while maintaining excellent properties for each component. By incorporating P atoms as dopants, the interaction between La, Cu, and P atoms not only facilitates fine-tuning of the electronic structure and optimization of the adsorption free energy (-OH), but also promotes an increase in catalytic active sites through sample size reduction, thereby further augmenting the performance of the OER.

NiO/ATO as an efficient bifunctional electrocatalysts for oxygen evolution and urea oxidation reactions

In this study, Ni-MOF-derived NiO was mixed with various weights of commercial antimony-doped tin oxide (ATO) using a simple and efficient hydrothermal method to synthesize composites denoted as AN-1, AN-2, and AN-3, which were subsequently characterized using a variety of physicochemical methods. The as-prepared materials were used as bifunctional electrocatalysts for oxygen evolution reaction (OER) and urea oxidation reaction (UOR). In the UOR, the AN-1 electrocatalyst exhibited excellent performance compared to the other electrocatalysts. In a 1.0 M KOH aqueous electrolyte, the OER onset potential was approximately 1.64 V, whereas, in the UOR, the overpotential was 1.38 V (vs RHE), which is lower than that of the OER. The AN-1 electrocatalyst showed lower Tafel slope values in both the OER and UOR studies: 173 mV dec−1 and 109mV dec−1, respectively.

Microwave fostered sustainable synthesis of Nb2O5 – ZnO nanomaterial for efficiency amplification in high performing energy systems

This study presents the first report on the microwave approach combined with improved sustainable synthesis of zinc oxide (ZnO) and niobium oxide (Nb2O5) to generate Nb2O5 – ZnO nanospheres. Following the development of nanospheres, the band gap energy decreased to 3.25 eV, and the average crystallite size was found to be 62.49 nm. The nanospheres had a mixed crystalline phase of hexagonal and orthogonal crystals. This material has demonstrated a predisposition towards hydrogen production in the electro-catalytic tests, with a minimal overpotential (ηHER) and a Tafel slope values of 127 mV and 125.6 mV dec-1. Furthermore, nanospheres decorated electrode remained intact in electrolyte environment for 1500 min and exhibited profound charge storage of 204.93 F g-1. 15% PV efficiency was attained by the air-processed perovskite solar cell thanks to the interface passivation functionality. The commendable performance of the binary Nb2O5 – ZnO nanospheres have validated their prospects for practical applications.

Design of NiPS3/MoS2/rGO hybrid electrocatalyst for electrochemical hydrogen evolution

The design and development of efficient electrocatalysts for hydrogen evolution reaction is presently a pressing task to overcome future energy demands. In the present study a hybrid layered compound NiPS3/MoS2/rGO (NMR) is investigated as an electrocatalyst for hydrogen evolution reaction (HER). The metal trichalcogenidophosphates (MTPs), transition metal dichalcogenides and reduced graphene oxide materials based electrocatalysts are promising material for HER. The hybrid layered compound NMR displays good electrocatalytic activity in acidic medium in comparison to its counterparts MoS2/rGO and NiPS3/rGO with an overpotential and Tafel slope of 152 mV vs RHE and 75 mV/dec, whereas MoS2/rGO and NiPS3/rGO shows an overpotential of 206 mV and 223 mV vs RHE with a Tafel slope value of 146 mV/dec and 154 mV/dec respectively. The hybrid electrocatalyst exhibited high stability up to 1000 cycles with a stable current. The high HER activity of NMR is attributed to synergistic effect of electrocatalysts where P and S of NiPS3 acts as an appropriate hydrogen adsorption sites and catalytically active Mo edge sites of MoS2 with high charge carrier property of rGO contributed to enhanced hydrogen evolution reaction.

Uniform carbon pillars array grown on boron doped diamond for high-performance supercapacitors and hydrogen evolution reactions

Carbon materials have marvelous ability in energy storage and microelectronics as a result of the high specific surface area and electrical conductivity. However, the low stability and the low power density caused by low potential window make it particularly difficult for their application in aqueous electrolysis. In this study, boron doped diamond (BDD) with wide potential window is used as substrate and Ni as catalyst to grow uniform carbon pillars (CP) by microwave plasma chemical vapor deposition method. The composite structure (CP/BDD) yields significant specific capacity (91.64 mF cm−2 at 0.1 mA cm−2) and cycling stability (92.3 % retention rate after 20,000 cycles) when used as the electrode of supercapacitors, superior to most of BDD-based electrodes. The prepared symmetrical supercapacitor devices maintain their excellent electrochemical performance characteristics (power density of 4.4 mW cm−2 and energy density of 13.4 μW h cm−2), as well as high cycling stability. In addition, the electrode has considerable application potential in electrochemical hydrogen production with low hydrogen evolution potential and small Tafel slope value. These results illustrate the potential of BDD based composites for using as energy storage electrodes for electronic products and energy conversion equipment.

Interfacial Regulation of Rice-Grain-like Iron-Nickel Phosphide Nanorods on Phosphorus-Doped Graphene Architectures as Bifunctional Electrocatalysts for Water Splitting.

The design of bimetallic metal-organic frameworks (MOFs) with a hierarchical structure is important to improve the electrocatalytic performance of catalysts due to their synergistic effect on different metal ions. In this work, the catalyst comprises bimetallic iron-nickel MOF-derived FeNi phosphides, intricately integrated with phosphorus-doped reduced graphene oxide architectures (FeNi2P-C/P-rGA) through the hydrothermal and phosphating treatments. The hierarchical architecture of the catalyst is beneficial for exposing active sites and facilitating electron transfer. The FeNi2P-C/P-rGA catalyst exhibits excellent performance in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline electrolytes. Notably, FeNi2P-C/P-rGA requires only the overpotential of 93 and 210 mV to achieve a current density of 10 mA cm-2 for the HER and OER with small values of Tafel slope and charge transfer resistance, respectively. Furthermore, the catalyst exhibits boosted activity for overall water splitting with a low potential of 1.56 V. This work can be considered to extend the design of multilevel catalysts in the application of water splitting.

Electrocatalytic oxygen reduction at non-metalated and pyrolysis free hypercrosslinked polymers

Oxygen reduction is one of the core steps of non-emissive zero carbon energy conversion. Therefore, enhancement of its sluggish kinetics is extremely important. Very recently researchers focused on oxygen electrocatalysis at porous polymers. Here we applied the non-metalated and pyrolysis free hypercrosslinked polymers with high specific surface area and abundant active sites. Electrode modified with the copolymer prepared from the twisted triphenylbenzene and N containing triphenyl amine exhibits electrocatalytic ORR in alkaline medium. Tafel slope value (0.067 V dec−1) indicates the efficient electrocatalytic activity and fast reaction kinetics. The lack of H2O2 product detected by scanning electrochemical microscopy suggests 4-electron path. The electrocatalytic activity of electrodes modified with hypercrosslinked polymers prepared from single monomers is also seen.

Pt nanoparticles loaded on three-dimensional porous carbon as electrocatalysts for hydrogen evolution reaction

The electrochemical catalytic hydrogen evolution reaction (HER) holds significant potential for the sustainable production of environmentally friendly hydrogen energy. Currently, the precious metal Pt is widely acknowledged as the most superior electrocatalyst. However, its limited availability and exorbitant cost impede its extensive application. In this study, low Pt-loaded three-dimensional (3D) porous carbon composites were successfully synthesized as catalysts using a template-free method and a high-temperature pyrolysis method. By evaluating the HER performance of different Pt concentrations of the catalysts Pt/C-X (X=0, 0.05, 0.1, 0.2, 0.4, 0.7 mmol) in acid solution, it was observed that the overpotential of Pt/C-0.2 reached as low as 17 mV with a significantly low Tafel slope value of 48 mV cm−2. Meanwhile, the Bilayer capacitance (Cdl) reached an impressively high value of 247.5 mF cm−2. Consequently, this also provides a promising way to enhance the catalytic performance of the loaded catalysts.

Attaining high-rate hydrogen evolution via SILAR deposited bimetallic nickel cobalt boride electrode: Exploring the influence of Ni to Co ratio

For the first time, a bimetallic Nickel Cobalt Boride (NCB) film with varying Ni to Co ratios was synthesized on stainless steel via the SILAR method. The NCB2 film (1:1 ratio) exhibited a mixed phase of metal boride and oxy-hydroxide with a highly porous, flaky-type morphology, while NCB1 (1:3 ratio) and NCB3 (3:1 ratio) showed only oxidized metal phases and agglomerated clusters. EDX confirmed the purity of the samples, and XPS indicated higher oxidation in NCB1 and NCB3 compared to NCB2. For HER, NCB2 showed the lowest overpotential (80 mV) compared to NCB1 (96 mV) and NCB3 (101 mV), and the smallest Tafel slope value (71 mV/dec). HER kinetics followed a Volmer-Heyrovsky mixed reaction path. NCB2 exhibited the highest Cdl value (16.55 mF/cm2) and the largest electrochemical active surface area (413.7 cm2), outperforming NCB1 (333.125 cm2) and NCB3 (205 cm2). At an overpotential of 100 mV, NCB2's TOF value was 8.23 s⁻1, higher than NCB1 (1.4 s⁻1) and NCB3 (1 s⁻1). For OER, NCB2 showed the highest Cdl value (106 mF/cm2) and ECSA value (2650 cm2). The Faradic efficiency of NCB2 was ∼98% after 190 h. Hydrogen evolution rates for NCB1, NCB2, and NCB3 as cathodes were 952 mL/h, 1022 mL/h, and 800.8 mL/h, respectively. In a prototype electrolyzer, NCB2 enhanced the hydrogen evolution rate by 30% in bifunctional mode to 1334.6 mL/h. After 100 h, performance declined by only 2.7% due to surface oxidation and phase changes. This achievement marks a milestone towards low-cost green hydrogen production, achieving the highest rate of hydrogen evolution as ever reported.

Elevating Oxygen Evolution using Iron Phthalocyanine Infused Vanillic acid Electrocatalyst.

Oxygen evolution reaction (OER) is the bottle neck step in water splitting reaction towards the realization of hydrogen based clean energy production and storage. Metal air batteries and polymer electrolyte membrane fuel cells (PEMFC) are the alternative green energy systems that utilise O2 and H2 in the production of continuous and high energy output without the utilization of carbon based fuels which are the major sources of pollution. Transition metal based N4 organics are explored extensively as oxygen electrocatalysts i. e., OER and oxygen reduction reaction (ORR) catalysts because of their ease of synthesis, tuneable properties, low cost and high performance with long term stability. Here, vanillic acid functionalized iron phthalocyanine (FeVAPc) was synthesised and characterised by various spectroscopic techniques. The novel FeVAPc exhibited good thermal stability and was coated on Ni foam for OER studies. The scanning electron microscopy images showed net-work like surface morphology and the X-ray photoelectron spectroscopy indicated the presence of Fe in +3 oxidation state. The Ni/FeVAPc demonstrated excellent electrocatalytic activity for OER with overpotential of 312 mV at 10 mA.cm-2 current density in 1.0 M KOH electrolyte. The designed organic based catalyst exhibited lesser Tafel slope value which is nearer to the benchmark catalyst, IrO2. The proposed catalyst exhibited good stability as phthalocyanines are highly stable and do not undergo decomposition even in strong acidic and basic corrosive media. Integration of FeVAPc onto the Ni foam resulted in higher mass activity, lower charge transfer resistance, high active surface area leading to enhanced conductivity and activity. The fabricated Ni/FeVAPc is an appropriate cost-effective, efficient and stable catalyst for OER towards industrial applications.

Exfoliated g-C3N4-CdS-MXene an efficient all-solid-state Z-type heterojunction serving as efficient photo/electro/photoeletro catalyst for oxygen evolution reaction and dye degradation under visible light at low bias voltage

The rational design of highly active catalysts for the photo/electro/photoelectro catalytic O2 evolution reaction (OER) and water treatment plays a crucial role in the development of sustainable energy generation and environment remediation technologies. Catalysts which are effective in solar light at a low external bias potential are in great demand. Herein, a novel catalyst consisting of all-solid-state Z-scheme g-C3N4-CdS-MXene heterojunction has been designed for photo/electro/photoelectro catalytic reactions. g-C3N4-CdS-MXene exhibited excellent photocatalytic efficiency towards Methylene Blue degradation under simulated solar light irradiation and superb electrocatalytic and photoelectron catalytic efficiency for OER. This catalyst showed high OER performance with an early onset potential of 1.58 V, a low overpotential of 350 mV (at 10 mA cm−2), and low value of Tafel slope (98 mV dec−1). When OER was combined with the photoelectro catalytic reaction for Methylene Blue degradation, g-C3N4-CdS-MXene demonstrated an exceptional photoelectro catalytic performance by degrading 100 % Methylene Blue within 4 min under solar light irradiation at a very low bias of 350 mV. This catalyst also exhibited its capability to degrade various dyes used in textile industries. This work provides an interesting strategy for simultaneous O2 production and efficient dye degradation for environmental and energy engineering.

Bimetallic NiCo Metal-Organic Frameworks with High Stability and Performance Toward Electrocatalytic Oxidation of Urea in Seawater.

The urea oxidation reaction (UOR) is an alternative anodic reaction for hydrogen generation via water splitting. The significance of UOR lies in both H2 production and the decontamination of urea-containing wastewater. Commercial electrocatalysts in this field are generally based on noble metals and show several limitations. Bimetal-organic frameworks (BMOFs) can be excellent candidates for the replacement of noble-metal-based catalysts beacuse of their promising features, such as a tunable structure, high surface area, and abundant sites for electrocatalysis. In this study, a series of nickel-cobalt BMOFs (Nix-Coy-BMOFs: x and y refer to a molar fraction of Ni and Co) were synthesized and applied as electrocatalysts in UOR. In particular, a Ni0.15Co0.85-MOF material with a structure similar to that of its parent Co-MOF, revealed exceptional electrocatalytic performance, as evidenced by low values of overpotential (1.33 V vs RHE at 10 mA cm-2), TOF (0.47 s-1), and Tafel slope (125 mV dec-1). At a 40 mA cm-2 current density, Ni0.15Co0.85-MOF also showed excellent stability during the 72 h tests. This performance of NiCo-BMOF can be assigned to the synergistic effect between Co and Ni, abundant active sites, porosity, and a tunable structure, all of which result in an increased reaction rate due to the acceleration of charge and mass transfers. Thus, the present work introduces an efficient noble-metal-free UOR for energy generation from urea-based wastewater.

Co‐W (Hydr)oxide with Ultralow Ru Promotes Water Dissociation Coupled H+ Abstraction in Alkaline HER

The hydrogen evolution reaction in alkaline water electrolysis is facilitated through the electrodeposition of trimetallic catalyst on nickel foam using the chronoamperometry technique. Specifically, the trimetallic catalyst CoWRu@NF is deposited onto a nickel foam substrate. The catalytic performance of this trimetallic catalytic electrode for the Hydrogen Evolution Reaction (HER) is then assessed in a 1.0 M potassium hydroxide (KOH) solution. This specially designed trimetallic catalytic electrode system efficiently provides the more active sites through the Co component. Subsequently, it facilitates the reduction of protons (H+) to generate hydrogen gas using the Ru component. Tungsten acts as a co‐catalyst in the system for water dissociation promotor by removing hydroxide formed after water dissociation and preventing the deactivation of Ruthenium by certain reaction intermediates. The CoWRu@NF trimetallic catalyst demonstrates excellent activity, showcasing a low overpotential (‐8 mV) to achieve a current density of ‐10 mA/cm2. Additionally, it exhibits low Tafel slope values (101.2 mV dec‐1), credited to the presence of cobalt and tungsten alongside Ruthenium in the catalytic system. This configuration is specifically designed to enhance the kinetics of the hydrogen‐evolving reaction.

Bifunctional Noble-Metal Free Ternary Chalcogenide Electrocatalysts for Water Splitting

With the ever-increasing global energy demand, the development of renewable energy technologies is crucial to fulfilling the energy requirements in a sustainable manner. Hydrogen has emerged as a promising energy carrier that can provide emission-free energy for end-use applications. Among the several pathways of hydrogen production, green hydrogen production by electrochemical water splitting using renewable energy is an emission-free, efficient energy conversion technology. Hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) occur at the cathode and anode, respectively. Water splits into hydrogen and oxygen at the thermodynamic potential of 1.23 V; however, overpotentials are observed experimentally due to the kinetic barriers, which increases the required potential for water splitting. Catalysts lower the required overpotentials, making the process more energy efficient. A significant issue with large-scale hydrogen production by water electrolysis is that the state-of-the-art catalysts for HER and OER are based on precious metals and thus are limited by their high cost and net production capacity. Thus, there is a lot of interest in developing noble-metal-free electrocatalysts based on earth-abundant materials that can efficiently lower the associated overpotentials for the two halves of the water-splitting reaction.A large number of late transition metal-based ternary complex oxides have been investigated for their catalytic performance towards water splitting, where fine-tuning of the properties using compositional engineering has been demonstrated. Binary sulfides, selenides, and phosphides have also been explored as candidates for water splitting. Recently, early transition metal-based ternary complex materials have emerged as a novel class of electronic materials with applications in infrared optics and photovoltaics. However, similar chalcogenide compositions based on late-transition metals remain underexplored.We have synthesized a series of LaMS3 (M = Mn, Fe, Co, Ni) materials by high-temperature sulfurization of corresponding ternary oxides, using carbon disulfide (CS2) as the sulfurizing agent. The LaMS3 compounds are isostructural and crystallize in the hexagonal P 63 space group. When tested for catalytic performance towards water splitting, they demonstrate good activity towards both HER and OER, with LaNiS3 (LNS) being the most active material, and a periodic activity trend is observed, where LNS > LCS >> LFS > LMS. For OER in alkaline electrolyte, LNS demonstrates an overpotential of 373 mV at 10mA/cm2 in 1.0 M KOH, and a low Tafel slope value of 48 mV/dec. The long-term stability was tested using chronopotentiometry measurements, and LNS shows excellent stability, with negligible change in overpotential over several hours. For HER testing in both acidic and alkaline electrolyte, LNS again seems to be the most active material, and a periodic activity trend in the HER activity of LaMS3 materials, similar to the OER activity trend, is observed. LNS has an overpotential of 340 mV in 0.5 M H2SO4 and 362 mV in 1.0 M KOH, indicating that LNS is catalytically active over a wide range of pH levels. LNS also shows excellent long-term stability towards HER in both acidic and alkaline electrolyte. We also compared the activity of LaMS3 materials with their ternary oxide counterparts from which they were synthesized, and the LaMS3 compounds outperform the LaMO3 compounds, demonstrating lower overpotentials and Tafel slope values for both HER and OER, with the HER overpotentials for LaMO3 materials being > 250 mV higher compared to LaMS3, for both acidic and alkaline electrolytes. The catalytic activity of the LaMS3 series towards both HER and OER, along with their excellent long-term stability, makes these materials promising candidates for bifunctional electrocatalysts for water splitting while offering a wide compositional range that allows for further optimization of their performance.

Surface Decorated SnOx modifiers Boost Oxygen Reduction and Hydrogen Evolution Reaction Performance of Pt Nanorods

The development of efficient, durable and commercially competitive catalysts for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is undoubtedly a challenging task for fuel cell technology. In this context, for the first time, we developed a bi-metallic heterogeneous nanocatalyst (NC) comprising high-density atomic SnOx-clusters anchored Pt-nanorods (denoted as SnOx@Pt) via formic acid reduction method (FAM) as a bifunctional catalyst for ORR and HER (Fig.1). The as-prepared SnOx@Pt nanorods exhibit unprecedented high mass activity (MA) of 160 mAmg-1 (Pt) at 0.85 V vs RHE in acidic ORR (0.5M HClO4), which outperformed the commercial J.M.-Pt/C (20 wt.% Pt) catalyst by 1.4 folds. Of special relevance, SnOx@Pt nanorods exhibit remarkable durability when operated up to 5000 cycles in accelerated durability test (ADT) and retain their 87% MA as that of the initial condition. Additionally, as-prepared SnOx@Pt nanorods demonstrated a notable lower overpotential (η) of 48 mV at the cathodic current density of 10 mAcm-2 and the Tafel slope of 33 mVdec -1 in acidic HER (0.5M H2SO4). These overpotential and Tafel slope values are significantly lower compared to commercial J.M.-Pt/C catalyst (η = 60 mV and Tafel slope = 38 mVdec-1). Moreover, such material retained its 100% performance in the chronoamperometric (CA) stability test up to 6h, which shows its capability in potential commercialization. The cross-referencing results of physical inspections and electrochemical analysis reveal that such a high-performance of SnOx@Pt nanorods is attributed to the local synergetic collaboration between SnOx modifiers and neighboring Pt active sites. More specifically, the SnOx modifiers promote the H-OH bond cleavage during HER, while simultaneously promotes the desorption of oxygen species on Pt surface in ORR, which later triggers the reduction reaction performances. Meanwhile, SnOx provides a shielding effect to Pt during harsh reduction conditions and thus high stability of SnOx@Pt nanorods is achieved. Of utmost importance, this study not only unveils a novel geometric design but also provides the mechanistic understanding behind the superior electrochemical properties of the unique SnOx modifiers in ORR and HER. Hence, we envision that the proposed rationale will be a forwarding step for the development of high-performance low Pt content catalysts for fuel cells with superior electrochemical properties far beyond the physical nature of transition elements. Keywords: Oxygen reduction reaction, hydrogen evolution reaction, fuel cells, nanocatalysts, mass activity