Electrocatalytic Surface Research Articles

Ni-based compounds in multiwalled graphitic shell for electrocatalytic oxygen evolution reactions

Here, we report a general strategy for designing a metal/carbon system, via a facile and environmentally friendly one-step approach, from metal acetate as an active electrocatalyst in oxygen evolution reaction (OER) during water decomposition. As a demonstration, a nanostructured Ni/C composite induced from nickel acetate is revealed in great detail. The resulting material is composed of: metallic nickel (Ni), nickel(II) oxide (NiO), and nickel carbide (Ni3C) coated with a graphitic shell and deposited on a carbon platform. Our findings underscore the prominent role of nickel species, including Ni0, Ni2+, and Ni3+, in driving the catalytic activity. Notably, the catalyst exhibits an overpotential of 170 mV, a Tafel slope of 49 mV·dec−1, an electrocatalytic surface area (ECSA) of 964.7 cm2, and a turnover frequency (TOF) value of 52.8 s−1, surpassing RuO2. The Raman spectra also suggest a graphitic "self-healing" phenomenon post-OER, attributed to the reduction of oxygen-containing groups. Carbon in the system (i) facilitates electron transfer, (ii) allows homogeneous distribution of Ni nanoparticles avoiding their agglomeration, and (iii) promotes durability of the electrocatalyst by serving as a protective barrier, shielding the core metal compounds. What is more, density functional theory (DFT) calculations allowed to optimized geometry of the model cluster Ni8O8(OH)8 describing two different sites on the β-NiOOH surface (001) and two different intermediates, (i)L-OOH and (ii)L-OOH. This facilitated to propose the reaction mechanisms involving both hydroxide ions and water molecules as reducers. Therefore, the chemisorption of OH− and H2O molecules at the NiOOH active center accompanied by bond breakage and the formation of a lattice hydroperoxide as an important intermediate is presumed. What is more, the proposed fabrication method for electroactive metal/carbon composites was validated with an iron and iron/nickel mixture.

Pressure-induced generation of heterogeneous electrocatalytic metal hydride surfaces for sustainable hydrogen transfer

Metal hydrides are crucial intermediates in numerous catalytic reactions. Intensive efforts have been dedicated to constructing molecular metal hydrides, where toxic precursors and delicate mediators are usually involved. Herein, we demonstrate a facile pressure-induced methodology to generate a cost-effective heterogeneous electrocatalytic metal hydride surface for sustainable hydrogen transfer. Taking carbon dioxide (CO2) electroreduction as a model system and zinc (Zn), a well-known carbon monoxide (CO)-selective catalyst, as a model catalyst, we showcase a homogeneous-type hydrogen atom transfer process induced by heterogeneous hydride surfaces, enabling direct hydrogenation pathways traditionally considered “prohibited”. Specifically, the maximal Faradaic efficiency for formate is enhanced by ~fivefold to 83% under ambient conditions. Experimental and theoretical analyses reveal that unlike the distal hydrogenation route for CO2 to CO over pristine Zn, the Zn hydride surface enables direct hydrogenation at the carbon site of CO2 to form formate. This work provides a promising material platform for sustainable synthesis.

Hydrothermally fabricated MoTe2/rGO as a proficient electrocatalyst for robust oxygen evolution reaction

The faster depletion of fossil fuels owing to overconsumption has encouraged the invention of eco-friendly energy conversion methods, resulting in an intensifying energy shortage and sustainability issues. The increasing energy demand compels researchers to investigate novel strategies for water electrolysis and energy conversion. However, fabricating a catalyst with minimal overpotential (η) for water oxidation is a difficult task. The recent research investigate the production of MoTe2 nanoparticles imbedded in rGO nanosheet to generate MoTe2/rGO composite using a hydrothermal technique. Various physical procedures were assessed to analyze the structure, vibrational modes, shape and elemental analysis of the prepared composite. The BET calculated surface area for the MoTe2/rGO composite is (62.3 m2 g−1), which is preferable for the OER procedure. The electrochemical results show that the composite exhibits a Tafel value (36 mV dec−1) with η of 201 mV at 10 mA cm−2 current density (j). Chronoamperometric analysis and cyclic endurance of the composite show stability for 42 h. The electrochemical outcomes show that incorporating rGO into MoTe2 increases electrocatalytic surface area, resulting in the greater adsorption of the electrolyte ions and active areas, allowing for rapid adsorption of electrolyte ions and lower resistance. The present study demonstrates a novel way for producing highly efficient rGO-based electrocatalysts, which improve OER efficiency and open up new paths for their widespread use in various applications.

Fabrication of covellite supported spinel oxide CuCo2O4 hybrid nano-composite electrode for efficient overall water splitting

Hydrogen fuel being a green source of energy got attention as no harmful by-products are produced on its combustion. Hydrogen generation by water splitting via effective electrocatalyst is imperative. This study reports the synthesis of CuCo2O4 supported on CuS via hydrothermal technique and use it as electrocatalyst for hydrogen generation. Electrocatalysis using CuS/CuCo2O4 electrode in alkaline media, shows remarkably low overpotential of 286 and 135 mV at benchmark current density of 10 mA cm−2 for oxygen evolution and hydrogen evolution reactions (OER and HER), respectively. Strain and dislocation cause more defects in composite leading to increase in active sites. Modest Tafel value of 170 and 61 mV/dec for HER and OER, accordingly suggesting improved electrocatalytic efficiency and reaction kinetics of CuS/CuCo2O4 nano-composite. The CuS/CuCo2O4 nano-composite also shows higher values of TOF and electronic conductivity than CuS and CuCo2O4. Evaluation of durability over a 50-hour period shows little current loss, demonstrating that the generated nanocomposite’s remarkable stability and it also shows high electrocatalytic active surface area (139.6 cm−2).

Unraveling the competition between the oxygen and chlorine evolution reactions in seawater electrolysis: Enhancing selectivity for green hydrogen production

Selective oxidation of water without production of chlorine during the electrolysis of seawater is a critical impediment towards obtaining green hydrogen. Indeed, understanding the complex competitive mechanisms of oxygen and chlorine formation at the anode is an analytic challenge. An argument for direct seawater electrolysis is presented with a dissection of the complications that arise at the anode in the presence of seawater ionic constituents such as the chloride ion. Electrolyser system durability and the impact on the current and voltage efficiencies are discussed. Critical challenges at the anode under the acidic conditions of proton exchange membrane water electrolysis interrelate the thermodynamic and kinetic constraints of the oxygen evolution reaction (OER) and the chlorine evolution reaction (CER) to elucidate the heterogenous mechanisms of the OER and the CER and the crucial stability predicament under selective OER electrocatalysis. The selectivity circumstances resolved by Density Functional Theory computations shed insight onto the reaction conditions that select for the preferred OER adsorbate chemisorption on the surface and substantiates the observed overpotentials required for the OER and CER; experimental rotating ring disk electrode analysis further indicate competitive adsorption of OER and CER reactants under an assumed Langmuir isotherm model. Identifying the rate determining step and breaking the scaling relationship of the AEM OER pathway may both improve the stability of the catalyst and achieve lower OER overpotentials. Critical insight is given into designing the heterogeneous electrocatalyst structure with selective facets, additional point defects, and augmented active site density through single atom catalysts. An argument for the utilization of ruthenium for its high natural ubiquity and modulable valence states that can facilitate atomic configurations with optimal active site d-band center energies to promote selective adsorbate binding is presented. Studies of in-situ filtration of the chloride ion under acidic conditions highlight the utility of manganese oxide and silica; the augmentation of the conductivity through manipulation of polaronic interactions; and the design of heterogeneous electrocatalysts with self-healing characteristics demonstrated in select molecular catalysts that may decrease the overpotential of the OER and achieve selectivity. It is with the hope that these design strategies provide insights into future research efforts to uncover an electrocatalytic surface selective for OER evolution under the perilous acidic conditions and reveal an effective solution as serendipitous as the abundancy of a natural resource such as seawater.

Exploring the Water Oxidation Catalytic Activity of a Mn-Based Magnetic Metal-Organic Framework: The Role of Proton Conductivity and Oxygen Evolution Reaction Overpotential.

The present work evaluates the water oxidation catalytic activity of a Mn-based metal-organic framework (MOF), which we envisioned to reduce the oxygen evolution reaction (OER) overpotential because of its high electrical conductivity, facilitated by solvent-encapsulated structural features. The presence of Mn centers induces interesting magnetic features in the MOF, which exhibits impressive cryogenic magnetic refrigeration with a ΔSM value of 29.94 J kg-1 K-1 for a field change of ΔH = 5T at 2.3 K. To the best of our knowledge, the ΔSM value of the current system ranked the highest position among the published examples. The crystal structure aligns perfectly with the thematic expectations and features as many as ten metal-coordinated water molecules, forming an extensive web of a hydrogen-bonded network while facing toward the porous channel filled with another set of much-anticipated entrapped lattice water molecules. Such structural features are expected to manifest high proton conductivity, and detailed investigation indeed yields the best value for the system at 1.57 × 10-4 S/cm at 95% humidity and 85 °C. In order to evaluate the thematic notion of a one-to-one relationship between OER and improved electrical conductivity, extensive electrocatalytic water splitting (WS) investigations were carried out. The final results show highly encouraging WS ability of the Mn-MOF, showing the electrocatalytic surface area value of the active species as 0.0686 F/g with a turnover frequency value of 0.043 [(mol. O2) (mol. Mn-MOF)-1 s-1]. Another fascinating aspect of the current communication is the excellent synergy observed between the experimental WS outcomes and the corresponding theoretical data calculated using density functional theory (DFT). Consequently, a plausible mechanism of the overall OER and the role of the Mn-MOF as a water oxidation catalyst, along with the importance of water molecules, have also been derived from the theoretical calculations using DFT.

Shape-Preserved CoFeNi-MOF/NF Exhibiting Superior Performance for Overall Water Splitting across Alkaline and Neutral Conditions.

This study reported a multi-functional Co0.45Fe0.45Ni0.9-MOF/NF catalyst for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and overall water splitting, which was synthesized via a novel shape-preserving two-step hydrothermal method. The resulting bowknot flake structure on NF enhanced the exposure of active sites, fostering a superior electrocatalytic surface, and the synergistic effect between Co, Fe, and Ni enhanced the catalytic activity of the active site. In an alkaline environment, the catalyst exhibited impressive overpotentials of 244 mV and 287 mV at current densities of 50 mA cm-2 and 100 mA cm-2, respectively. Transitioning to a neutral environment, an overpotential of 505 mV at a current density of 10 mA cm-2 was achieved with the same catalyst, showing a superior property compared to similar catalysts. Furthermore, it was demonstrated that Co0.45Fe0.45Ni0.9-MOF/NF shows versatility as a bifunctional catalyst, excelling in both OER and HER, as well as overall water splitting. The innovative shape-preserving synthesis method presented in this study offers a facile method to develop an efficient electrocatalyst for OER under both alkaline and neutral conditions, which makes it a promising catalyst for hydrogen production by water splitting.

Toward understanding CO oxidation on high-entropy alloy electrocatalysts

Extended high-entropy alloy electrocatalysts as a platform to investigate electrocatalytic CO oxidation and surface structure–property relations.

Electrocatalytic activity of tungsten carbide hybrids with two different MOFs for water splitting: a comparative analysis.

Conventional energy resources are diminishing, and environmental pollution is constantly increasing because of the excessive use of fossil fuels to sustain the ever-increasing population and industrialization. This has raised concerns regarding a sustainable future. In the pursuit of addressing sustainability in industrial processes and energy systems, the production of green hydrogen is considered a promising and crucial solution to meet the growing energy demands. Water-splitting is one of the most effective technologies for producing clean and carbon-neutral hydrogen. Water-splitting is a scientifically emerging application, but it is commercially limited due to its economic non-viability. The sluggish kinetics and the high overpotential needed for the water-splitting reactions (HER and OER) have encouraged the scientific community to design electrocatalysts that address the concerns of low activity, efficiency and stability. Designing a hybrid catalyst using metal-organic frameworks (MOFs) with transition metal carbides can be a suitable approach to address the deficiencies of conventional water-splitting catalysts. In this study, we have designed and fabricated an electrocatalyst of tungsten carbide (WC) with two different MOFs (Zr-based and Fe-based) and explored their electrocatalytic activity for hydrogen generation in an alkaline medium. It should be noted that hybrids of tungsten carbide with a zirconia MOF (UiO-66) showed better electrocatalytic activity with low overpotentials of 104 mV (HER) and 152 mV (OER) at a current density of 10 mA cm-2. This superior activity of WC with the Zr-MOF in comparison to the Fe-MOF is due to the synergistic effect of Zr present in UiO-66 grown on the WC matrix. Moreover, UiO-66 provides a larger electrocatalytic active surface area, so available active sites are more in UiO-66 as compared to the Fe-MOF. These findings set the stage for the systematic development and production of bi-functional hybrid catalysts with the potential to be utilized in water-splitting processes.

Green fabrication of ultrafine N-Mo x C/CoP hybrids for boosting electrocatalytic water reduction

Developing non-noble-metal electrocatalysts for hydrogen evolution reactions with high activity and stability is the key issue in green hydrogen generation based on electrolytic water splitting. It has been recognized that the stacking of large CoP particles limits the intrinsic activity of as-synthesized CoP catalyst for hydrogen evolution reaction. In the present study, N-Mo x C/CoP-0.5 with excellent electrocatalytic activity for hydrogen evolution reaction was prepared using N-Mo x C as decoration. A reasonable overpotential of 106 mV (at 10 mA cm−2) and a Tafel slope of 59 mV dec−1 in 1.0 M KOH solution was achieved with N-Mo x C/CoP-0.5 electrocatalyst, which exhibits superior activity even after working for 37 h. Uniformly distributed ultrafine nanoclusters of the N-Mo x C/CoP-0.5 hybrids could provide sufficient interfaces for enhanced charge transfer. The effective capacity of the hydrogen evolution reaction could be preserved in the complex, and the enlarged electrocatalytic surface area could be expected to offer more active sites for the reaction.

Bubble Management for Electrolytic Water Splitting by Surface Engineering: A Review.

During electrocatalytic water splitting, the management of bubbles possesses great importance to reduce the overpotential and improve the stability of the electrode. Bubble evolution is accomplished by nucleation, growth, and detachment. The expanding nucleation sites, decreasing bubble size, and timely detachment of bubbles from the electrode surface are key factors in bubble management. Recently, the surface engineering of electrodes has emerged as a promising strategy for bubble management in practical water splitting due to its reliability and efficiency. In this review, we start with a discussion of the bubble behavior on the electrodes during water splitting. Then we summarize recent progress in the management of bubbles from the perspective of surface physical (electrocatalytic surface morphology) and surface chemical (surface composition) considerations, focusing on the surface texture design, three-dimensional construction, wettability coating technology, and functional group modification. Finally, we present the principles of bubble management, followed by an insightful perspective and critical challenges for further development.

3D printed carbon black-polylactic acid/copper (CB-PLA/Cu) sensor for improved sustainability in monitoring photocatalytic hydrogen peroxide evolution

As the photocatalytic generation of hydrogen peroxide continues to gather increasing interest, there is a significant need to introduce more sustainable methods to monitor the reaction process. The fabrication of low-cost sustainable electrochemical sensors offers an enticing alternative to the current standard methods. This study reports the first use of an electrochemical sensor to monitor such a process. A highly reproducible 3D printed carbon black-polylactic acid/copper sensor with an extremely low fabrication cost of €0.012 was employed to accurately monitor the photocatalytic evolution of hydrogen peroxide. The accuracy was confirmed through strong correlation with a standard fluorescence spectroscopic method. The sensor displayed limit of detection and limit of quantification values of 0.24 µM and 0.79 µM respectively, and a sensitivity of 217 µA mM−1 cm-2, while also showing strong selectivity towards hydrogen peroxide in the presence of potential interfering species. Moreover, the electrocatalytic surface was capable of ≥ 3x regeneration without significant loss in activity bringing a ≥ 75 % decrease in analysis cost and a significant reduction in potential waste material. This novel approach to monitoring the photocatalytic evolution of hydrogen peroxide presents as a more economical and sustainable alternative to current methods.

Stimulation of electron transfer in electricigens by MnxCoySz heterostructure for the enhanced power generation of microbial fuel cell

Microbial fuel cells (MFCs) are an efficient approach to converting energy existing in waste into electricity. However, MFCs still face problems such as low electron transfer rate and low power density. Herein, the anode properties dominate the performance of MFC. This study manufactured a high-performance MnCo2S4–CoS1.097/carbon black carbon felt (T-MCS-CS/CB-CF) anode through a two-step hydrothermal method. T-MCS-CS/CB catalyst exhibited superior surface roughness and mesoporous structure. Besides, the excellent electrocatalytic activity of the T-MCS-CS/CB catalyst with the heterostructure resulted in the higher power output. After biofilm formation, T-MCS-CS/CB-CF anode exhibited lower Rct (9.29 Ω) than MnCo2S4-Co4S3/ carbon black carbon felt (MCS-CS/CB-CF (15.83 Ω)), carbon black carbon felt (CB-CF (29.52 Ω)) and CF anode (116.1 Ω), exhibiting higher electrochemical activity. T-MCS-CS/CB-CF anode enhanced extracellular electron transfer (EET) and improved the power density, which was 12.29 times higher (1299.27 mW/m2) than the bare CF (105.70 mW/m2). The relative abundance of Geobacter for T-MCS-CS/CB-CF (21.65 %) was 7.24 times higher than the control CF anode (2.99 %). Moreover, T-MCS-CS/CB modification enriched exoelectrogens/sulfate-reducing bacteria, Desulfovibrio, 4.69 % higher than the CF anode, which attributed to the introduction of CoS1.097. The excellent electrocatalytic activity, surface properties and biocompatibility of T-MCS-CS/CB-CF promoted the power output in MFC. This study provided an effective way of anodic electrocatalyst fabrication for enhancing the power generation of MFC.

Aloe vera extract mediated hydrothermal synthesis of rose-like copper iron sulfide for efficient oxygen evolution reaction

BackgroundFabricating electrocatalysts with high surface area is salient to attain water splitting reaction with high efficiency. Conventionally, complexing agent assisted hydrothermal synthesis is often used to synthesize electrocatalyst with unique morphologies that could improve the electrocatalytic surface area. MethodIn this work, a novel approach of adopting aloe vera extract as green complexing agent was used to fabricate copper iron sulfide (CuFeSx)-based nanostructure on nickel foam. Different ratios of aloe vera extract and water were used to identify the effect of complexing agent on morphology of the material. Significantfindings FESEM micrographs verified the role of aloe vera extract as green complexing agent that formed nanorose-like morphology when 75% aloe vera was used. The optimized composition showed that only 234 mV overpotential was required upon iR-compensation to attain 100 mA cm−2 with a corresponding Tafel slope of 81 mV dec−1. Electrochemical surface area analysis (ECSA) revealed that high surface area exposure aided in lowering the overpotential to achieve high current density. The electrocatalyst exhibited good stability upon sustained exposure to alkaline medium for 48 h, retaining up to 84% of its initial current density. This study highlights the potential of using phytochemical-mediated synthesis to fabricate electrocatalysts for generation of sustainable hydrogen fuel via water splitting.

Packed OV-SnO2-Sb bead-electrodes for enhanced electrocatalytic oxidation of micropollutants in water

Electrocatalytic oxidation is an appealing treatment option for emerging micropollutants in wastewater, however, the limited reactive surface area and short service lifetime of planar electrodes hinder their industrial applications. This study introduces an innovative electrochemical wastewater treatment technology that employs packed bead-electrodes (PBE) as a dynamic electrocatalytic filter on a dimensionally stable anode (DSA) acting as a current collector. By using PBE, the electroactive volume is expanded beyond the vicinity of the common planar anode to the thick porous media of PBE with a vast electrocatalytic surface area. This greatly enhances the efficiency of electrochemical degradation of micropollutants. The OV-SnO2-Sb PBE filter achieved a nearly 100 % degradation of moxifloxacin (MOX) in under 2 min of single-pass filtration, with a degradation rate over an order of magnitude higher than the conventional electrochemical oxidation processes. The generation of abundant radical species (•OH) and non-radical species (1O2 and O3), along with the enhanced direct oxidation, led to the outstanding performance of the charged PBE system in MOX degradation. The OV-SnO2-Sb PBE was remarkably stable, and the separation between the electroactive PBE layer and the base Ti anode allows for easy renewal of the bead-electrode materials and scaling up of the system for practical applications. Overall, our study presents a dynamic electroactive PBE that advances the electrocatalytic oxidation technology for effective control of emerging pollutants in the water environment. This technology has the potential to revolutionize electrochemical wastewater treatment and contribute to a more sustainable future environment.

High phase purity of stable 1T-phase Co-doped WS2 for full pH hydrogen evolution reaction in water and seawater

Metallic 1T phase transition metal dichloride (TMDs) shows excellent catalytic activity for the hydrogen evolution reaction (HER), but stabilization of 1T phase TMDs is still challenging. Herein, the Finke-type POMs K10[Co4(H2O)2(PW9O34)2] [Co4(PW9)2] was used for the first time as a precursor to obtaining size ∼ 4 nm, highly dispersed 1T-WS2 in the hollow mesoporous carbon sphere (HMCS) by the effect of confinement, named 1T-CoWS/HMCS. 1T-WS2 was obtained based on the natural Co-W atomic interface of POMs and further enhanced dispersion at the molecular and nano scales. 1T-CoWS/HMCS only requires ultralow overpotential with high electrocatalytic surface area and robust stability in water and seawater. According to DFT calculations, the Co-S-edge site of 1T-CoWS significantly reduced the rate-limiting step of HER as the predominant active site. This work provides a worthy reference for the synthesis of high-quality metastable TMDs.

Enhanced Hydrogen Evolution Performance of Ni−Mo-Based Electrocatalysts in Seawater by Controlling Surface Wettability

Environmental pollution and global warming have become enormous problems all over the world. At the United Nations Climate Change Conference, carbon neutrality was proposed as a way to solve this problem through the Paris Agreement in 2015. To achieve zero net carbon dioxide emissions, research on how to obtain energy from renewable energy resources has been intensively conducted. Among various candidates of renewable chemical fuels, green H2, produced by water electrolysis is considered as one of the promising, next generation chemical fuels.Almost 97% of earth’s water resources exist as seawater. Moreover, seawater has an advantage that it can be used as an electrolyte owing to the various ions, existing naturally. Therefore, one of the ultimate goals in green H2 generation is to directly utilize seawater as the electrolyte source.Although Pt-group materials (PGMs) are well known catalysts in hydrogen evolution reaction (HER) but one of the main challenges for wide commercialization with PGMs is its high cost and scarcity. In order to overcome this issue, research on HER catalysts using non-PGM (NPGM) has been intensively performed. Among various NPGM elements, Ni−Mo has great potential for electrocatalysts in HER owing to its cost effectiveness as well as their high electrocatalytic activities in wide pH range of electrolytes. It is well known that not only the electrocatalytic activity in HER, mainly originating from chemical compositions at the surface, but also the physical surface properties, especially the surface wettability, play an important role to regulate the electrocatalytic performance. The evolved bubbles by the HER form the solid−gas−liquid interfaces, which results in the turn-off of the active sites toward electrochemical reactions until the gas bubbles remove from the electrocatalytic surface. Previous studies reveal that this dynamic, evolutionary behavior of surface active sites by the bubble growth/departure significantly influence the electrocatalytic performance.Herein, we demonstrate the Ni−Mo-based material as the electrocatalyst toward HER in simulated seawater, which is 0.5 M phosphate buffer with 0.6 M NaCl. The electrocatalytic layers are deposited by simple electrodeposition with the aminated graphene oxide (aGO) to form composites (aGO/NiMo). The addition of aGO in Ni−Mo does not influence the electrocatalytic activity in HER, exhibiting nearly the same cyclic voltammograms with pure NiMo. Interestingly, the long-term performance of aGO/NiMo, however, is observed when compared to the pure NiMo. The enhanced durability by chronopotentiometric measurements in the aGO/NiMo is ascribed to the improved surface wettability, originating from added aGO. The images taken by high-speed camera clearly show that the H2 bubbles with smaller sizes at the surface of aGO/NiMo but much larger density than the ones at pure NiMo are observed. These phenomena denotes that the regeneration rate of active sites by bubbles departure from the surface is much higher in the aGO/NiMo than NiMo without aGO, indicating that the aGO is beneficial for improving the surface wettability. The longer residence of H2 bubbles at the pure NiMo increases the actual overpotential applied in the single active site under constant current density, leading to the faster degradation of electrocatalytic activity in HER. The physical properties of surface between aGO/NiMo and NiMo for surface wettability is also supported by surface roughness measurements in atomic force microscope and contact angles. Our study contributes to the fundamental design of the physical properties of electrocatalytic surfaces physical properties, thereby simply improving the electrochemical performance in HER.

Highly-efficient removal of Rhodamine B using a flow-through electrocatalytic filtration system: Characteristics, efficiency and mechanism

The objective of this research is to develop an effective electrocatalytic filtration system using Ti/SnO2-Sb membrane anodes for eliminating Rhodamine B (RhB) from wasteater. Compared to Ti/SnO2-Sb plate anode, the prepared Ti/SnO2-Sb membrane anodes featured smaller particle size, bigger electrocatalytic active surface area, lower charge transfer resistance, and higher potential for oxygen evolution. The electrocatalytic filtration system obtained RhB removal of 90.29% with EE/O of 5.51 kWh m−3 after 90 min of electrolysis when initial pH value was 5, current density was 10 mA cm−2, initial RhB concentration was 50 mg L−1, and membrane flux was 2.17 m3 (m2·h)−1, respectively. The flow-through electrocatalytic filtration system was found to be limited by kinetics under a high membrane flux and dominated by an indirect radical oxidation. Finally, the possible RhB degradation pathways were proposed based on the detected intermediates and density functional theory calculations.

ZnO nanoparticles-copper metal-organic framework composite on 3D porous nickel foam: a novel electrochemical sensing platform to detect serotonin in blood serum

Herein, we report a simple non-enzymatic electrochemical sensor for the detection of serotonin (5-HT) in blood serum using ZnO oxide nanoparticles-copper metal-organic framework (MOF) composite on 3D porous nickel foam, namely, ZnO-Cu MOF/NF. The x-ray diffraction analysis reveals the crystalline nature of synthesized Cu MOF and Wurtzite structure of ZnO nanoparticles, whereas SEM characterization confirms the high surface area of the composite nanostructures. Differential pulse voltammetry analysis under optimal conditions yields a wide linear detection range of 1 ng ml−1 to 1 mg ml−1 to 5-HT concentrations and a LOD (signal to noise ratio = 3.3) of 0.49 ng ml−1, which is well below the lowest physiological concentration of 5-HT. The sensitivity of the fabricated sensor is found to be 0.0606 mA ng−1 ml−1.cm2, and it exhibited remarkable selectivity towards serotonin in the presence of various interferants, including dopamine and AA, which coexist in the real biological matrix. Further, successful determination of 5-HT is achieved in the simulated blood serum sample with a good recovery percentage from ∼102.5% to ∼99.25%. The synergistic combination of the excellent electrocatalytic properties and surface area of the constituent nanomaterials proves the overall efficacy of this novel platform and shows immense potential to be used in developing versatile electrochemical sensors.

Phase engineering and surface reconstruction of CrxMnFeNi high entropy alloys for electrocatalytic water splitting

The quest for cost-effective and efficient catalysts for oxygen and hydrogen evolution reactions is vital for a carbon-neutral future. High entropy alloys (HEAs), known for their exceptional thermodynamic stability and performance, have recently emerged as promising candidates in this field. Yet, the relationship between the phase and catalytic performance in HEAs remains understudied. Commonly, metallic catalysts undergo surface reconstruction under high oxidizing potentials under the oxygen evolution reaction (OER), making the identification of the truly active species essential for designing efficient catalysts. Nonetheless, characterization of surface reconstruction of nanoscale HEAs is challenging due to low content of each metal, exacerbated by the use of nonmetal support during synthesis. In this study, we unveil the phase-performance relationship in HEAs and identify that the body-centered cubic (BCC) phase CrMnFeNi outperforms its face-center cubic (FCC) phase counterparts in catalyzing both OER and the hydrogen evolution reaction (HER) due to its superior electrical conductivity and optimized electronic structures. Particularly, Cr1.5MnFeNi with the most prominent BCC phase demonstrates superior OER activity (η10 of 255 mV and Tafel slope of 28.7 mV dec−1), surpassing other Cr, Mn, Fe, Ni-based catalysts, and even state-of-the-art RuO2. X-ray photoelectron spectroscopy (XPS) analysis a transition of Mn, Fe, and Ni elements from metallic states to oxidation states, with surface dissolution of Cr after OER durability tests. This research elucidates the phase-dependent electrocatalytic performance and surface reconstruction in HEAs, providing valuable insights for designing and optimizing HEA materials for electrocatalytic applications.