Earth-abundant Electrocatalysts Research Articles

Probing the structural evolution of cobalt hydroxide in electrochemical water splitting.

Transition-metal hydroxides are a category of earth-abundant and stable electrocatalysts for energy storage and conversion devices involving sluggish oxygen evolution reaction (OER). Understanding dynamic evolution at the solid/liquid interface of transition-metal hydroxides is crucial for the rational design of high-performance OER electrocatalysts. This study implemented in situ electrochemical atomic force microscopy (EC-AFM) to directly image the dynamic structural evolution of α-Co(OH)2 platelets during the electrochemical OER. Reconstruction of α-Co(OH)2, accompanied by ion insertion from the electrolyte, results in a volume expansion, which can be well confirmed from the X-ray diffraction patterns. Our findings are important for the fundamental understanding of transition-metal hydroxide oxygen-evolution catalysts, illustrating the dynamic nature of Co-based nanostructures under electrochemical conditions.

Doping-mediated interface engineered Ni3S2: Economically viable electrochemical methanol-mediated water splitting

Electrochemical water splitting is the front runner to meet the global green hydrogen demand. The development of a noble metal-free earth-abundant electrocatalyst is desired to rationalize an economically viable electrochemical water-splitting system. The sluggish anodic oxygen evolution reaction (OER) is the bottleneck of the electrochemical water-splitting system. Herein, to improve OER kinetics, group VIB elements such as chromium (Cr), molybdenum (Mo), and tungsten (W) doped nickel sulfides (Ni3S2) nanosheets (NSs) are synthesized by two-step hydrothermal method to modulate the intrinsic electrocatalytic activity of the pure Ni3S2. Among all the doped samples, the Cr-doped Ni3S2 catalyst exhibited excellent OER with an ultra-low overpotential of 248 mV and MOR with a potential of 1.36 V @ 10 mA cm−2 achieving a lower Tafel slope of 95.5 mV/dec and 46.4 mV/dec and outstanding durability with negligible degradation respectively. Furthermore, the Pt/C||Cr-Ni3S2 (1.48 V) system outperforms commercial Pt/C||RuO2 (1.52 V @ 10mA cm−2) in a two-electrode configuration. The methanol-mediated hybrid water splitting system only warranted a cell voltage of 1.38 V to attain 10 mA cm−2 for the Pt/C||Cr-Ni3S2 system in the presence of 0.1 M MeOH. The methanol oxidation reaction (MOR) mediated the hybrid water electrolyzer system demonstrates reduced operation cell voltage while additionally electro-synthesizing formate as a value-added chemical. The overall work is motivated to rationalize the importance of doping-mediated interface-engineered catalyst synthesis to improve the electrocatalytic efficiency of the hybrid water electrolyzer.

Solar-driven methanol to formate conversion coupled with energy-efficient hydrogen production through Cr dopant-induced charge transfer modulation at the in-situ formed FeOOH/FeCo-LDHs interface

The goal of developing efficient electrocatalysts that can effectively accelerate both the hydrogen evolution reaction (HER) and the methanol oxidation reaction (MOR) is essential. Additionally, overcoming the sluggish anodic oxygen evolution reaction (OER) also presents a considerable challenge for achieving energy-efficient hydrogen (H2) production. Herein, we report the synthesis of self-supported hierarchical FeOOH/Fe0.5CoCr0.5-LDHs as an advanced electrocatalyst by employing simultaneous engineering strategies for producing the formate from MOR at the anode while simultaneously generating H2 at the cathode. Both the experimental and theoretical studies demonstrate the superior charge transfer enabled by the in-situ formed heterostructure. Additionally, electronic modulation due to Cr intercalation, and the presence of a superhydrophilic hybrid surface morphology promote the remarkable electrocatalytic activity and stability of the FeOOH/Fe0.5CoCr0.5-LDHs electrocatalyst. The overall water splitting process required a cell voltage of 2.01 V to achieve a current density of 50 mA cm−2, whereas a lower cell voltage of 1.76 V was sufficient for overall methanol oxidation. Remarkably, a solar-driven system prototype, consisting of a commercial Si cell combined with a methanol splitting electrolyzer comprising FeOOH/Fe0.5CoCr0.5-LDHs electrodes, achieved a photocurrent density of 8.1 mA cm−2 over 2 h. This work demonstrates the capability of earth-abundant elements-based electrocatalysts for sustainable and selective electrochemical synthesis. As a result, it enables the energy-efficient generation of clean H2 and valuable chemicals byproducts.

Surface active sites and interphase engineering into metal oxide hydrates enabled by ions substitution for efficient water splitting

The expanding requirement of energy-effective and cost-efficient water electrolysis has prompted studies of earth-abundant metal-based electrocatalysts. In this study, we study the typical substitution strategy of cation (Pt) or anion (Se) for modifying surface active sites or interphase engineering to tune electronic structure of bimetallic nickel molybdenum oxide hydrates (NiMoO4·xH2O), thus effectively improving catalytic properties toward hydrogen evolution reaction (HER) or oxygen evolution reaction (OER). Result of the cation substitution achieves PtSA–NiMoO4·xH2O catalyst with abundant doped Pt single atoms on surface, which promotes high HER activity with a small overpotential of 73 mV at a current yield of 10 mA cm−2 in alkaline medium. Meanwhile, Se–NiMoO4·xH2O catalyst, an outcome of the anion substitution approach, has unique interfaces of NiSe-NiMoO4 heterostructure and thus exhibits a desired overpotential of only 297 mV for OER. The combination of PtSA–NiMoO4·xH2O(–)//Se–NiMoO4·xH2O(+) couple results in a two-electrode electrolyzer cell, which requires a small cell voltage of 1.48, 1.54, and 1.59 V to deliver a response of 10 mA·cm−2 at 75, 50, and 25 °C, respectively, along with negligible performance decay during 50 h operation. These results highlight the potential of our catalyst engineering strategies to achieve high-performance green hydrogen production.

Hierarchical Bifunctional NiO Electrocatalyst: Highly Porous Structure Boosting the Water Splitting Activity.

The development of an efficient, low-cost and earth-abundant electrocatalyst for water splitting is crucial for the production of sustainable hydrogen energy. However their practical applications are largely restricted by their limited synthesis methods, large overpotential and low surface area. Hierarchical materials with a highly porous three-dimensional nanostructure have garnered significant attention due to their exceptional electrocatalytic properties. These hierarchical porous frameworks enable the fast electron transfer, rapid mass transport, and high density of unsaturated metal sites and maximize product selectivity. Here the process involved obtaining monodispersed microrod-shaped Ni(OH)2 through a hydrothermal reaction, followed by a heat treatment to convert it into hierarchical microrod-shaped NiO materials. N2 sorption analysis revealed that the BET surface area increased from 9 to 89 m2/g as a result of the heat treatment. The hierarchical microrod-shaped NiO materials demonstrated outstanding bifunctional electrocatalytic water splitting capabilities, excelling in both HER and OER in basic solution. Overpotential of 347 mV is achieved at 10 mA/cm2 for OER activity, with a Tafel slope of 77 mV/dec. Similarly, overpotential of 488 mV is achieved at 10 mA/cm2 for HER activity, with a Tafel slope of 62 mV/dec.

Electrolyte-Induced Fe-Doping of LaNiO3 Model Surfaces for Water Electrolysis

Renewable energy needs to be store in different energy forms for the energy transition away from fossil fuels. One of most promising forms is chemicals such as H2 and C-based fuels obtained via electrochemical reactions. The common hinderance in such reactions is the sluggish oxygen evolution reaction (OER), which causes low energy efficiency in conversion devices. Developing highly active, earth-abundant OER electrocatalysts in alkaline media is necessary to boost the performance of such devices. Fe ion content in electrolyte is known to influence the OER-activity of metal oxide electrocatalysts. For example, the Fe incorporation in NiOOH is a well-established and important effect for OER.[1] Here, we present the effect of absorbed Fe on the OER activity of the epitaxial Ni-surface terminated LaNiO3 thin films. The correlation between surface species and OER activity of electrocatalysts was investigated using surface-sensitive low-energy ion scattering and X-ray photoemission spectroscopies. We observe more than an order-of-magnitude boost in OER activity during initial cycling, from 0.15 mAcm-2 to 3.40 mAcm-2 at 1.60 V vs. reversible hydrogen electrode. The activity increase was mainly caused by the incorporation of up to 5 % Fe at the top surface of LaNiO3 film (less than ~1 nm) even though only a very trace amount of Fe ion, 30 ppb, is present in the 0.1 M electrolyte of high purity KOH 99.99 %. Our results demonstrate that the disordered active surface phase, which develops even on single crystalline surfaces, is a complex interplay between the as-prepared (surface) crystalline structure, composition of the solid electrocatalyst and the liquid electrolyte, and has strong impact on the final OER activity, implying that we need to think differently about the crystalline electrocatalysts: crystalline bulk and dynamically changing surface layer.[1] L. Trotochaud, S.L. Young, J.K. Ranney, S.W. Boettcher, Nickel–Iron Oxyhydroxide Oxygen-Evolution Electrocatalysts: The Role of Intentional and Incidental Iron Incorporation, J. Am. Chem. Soc. 136 (2014) 6744–6753.

Synthesis of Yolk-Shell CoNi2S4 Spheres Modified Flexible Carbon Cloth Electrode for Highly Sensitive Detection of Neurotransmitter Dopamine

Dopamine (DA) is a neurotransmitter that is connected with transitory information in the mammalian central nervous system; changes in its concentration in the body are directly related to mental activity. The absence and/or low level of DA can cause symptoms of several disorders, including Parkinson’s and schizophrenia. As a result, detecting DA in patients is critical for regulating body function. Many efforts have been made to build electrochemical sensing devices to detect DA in human body or biological fluids due to its inherent advantages of high sensitivity, speed, simplicity, and affordability. However, surface modification with nanomaterials, polymers, pretreatments, or simple functionalization are required to improve the performance of these sensing electrodes. Further, exploration of earth-abundant electro-catalysts with high activity and stability is also important for the development of highly selective and sensitive electrochemical sensing interfaces. With these considerations in mind, our study describes the construction of yolk-shell CoNi2S4 spheres modified flexible carbon cloth (CC) electrode for the sensitive detection of DA. The synthesized material's surface and morphological study were examined, and the successful synthesis was confirmed. The yolk-shell CoNi2S4 spheres shown good electrochemical sensing performance towards DA detection due to their unique surface morphology with large specific surface area and synergistic effects. In comparison to unmodified CC, the yolk-shell CoNi2S4 spheres modified CC demonstrated a low detection limit (5.1 nM), great sensitivity, and a wide linear range (0.01 – 5.2 µM). The detection selectivity was also tested in the presence of a high quantity of the common interference ascorbic acid. Selectivity, stability, and repeatability have also been demonstrated to be satisfactory. Furthermore, the fabricated sensor’s flexibility endows it with significant potential in the fabrication of wearable and soft electronics for human healthcare monitoring.

Investigation of the Activity and Stability of Manganese-Based Electrocatalysts for the Electrochemical Oxidation of Water and Small Organic Molecules in Acidic Electrolyte

Water electrolysis is a crucial process for hydrogen production, providing a clean and sustainable method for H2 production. Iridium-based catalysts are particularly effective in promoting the oxygen evolution reaction (OER) that takes place at the anode of electrolyzers. The unique properties of iridium make it well-suited for this purpose, but its high cost becomes a bottleneck in making water electrolysis economically viable on a large scale. Manganese-based electrocatalysts have emerged as promising candidates for the OER, mainly due to their earth abundance, low toxicity, and activity. It has been shown that manganese oxide can operate stably in acid, in a restricted potential window, where the formation of permanganate ions is avoided. Thus, for practical application, the stability must be improved, so a larger potential window can be employed. To address this challenge, some approaches have emerged from combining a catalytically active, but instable oxide, with the one that is stable, but inactive for the OER. In the presentation, we will show the results of activity, stability, and faradaic efficiency (FE) for O2 formation for water electro-oxidation on manganese oxide, and on manganese oxide combined with antimony, tin, titanium, niobium, and silicon oxide. The faradaic efficiencies, determined via EC-MS (Electrochemistry coupled to mass spectrometry) measurements revealed that manganese antimonate and pure manganese oxide have the highest values for O2 formation, with the former presenting higher stability at high overpotentials. We will discuss the obtained trends in stability and FEs for the other synthesized oxides. Additionally, for these two most efficient electrocatalysts, EC-MS measurements were conducted for the electrochemical oxidation of some small organic molecules, such as formic acid, methanol, ethanol, and ethylene glycol (electrochemical reforming for H2 production). The results showed that the selectivity for the electro-oxidation of water and/or of the organic molecule (monitoring the formation of CO2) strongly depends on the catalyst composition and on the number of carbon atoms of the molecule. We will further discuss, in the presentation, the factors that govern the selectivity and stability for each case. The obtained results of this study may be helpful for developing more efficient, selective and, mainly, more stable earth-abundant electrocatalysts for electrolyzers.

Transition metals-based electrocatalysts on super-flat substrate for perovskite photovoltaic hydrogen production with 13.75% solar to hydrogen efficiency

Harnessing the inexhaustible solar energy for water splitting is regarded one of the most promising strategies for hydrogen production. However, sluggish kinetics of oxygen evolution reaction (OER) and expensive photovoltaics have hindered commercial viability. Here, an adhesive-free electrodeposition process is developed for in-situ preparation of earth-abundant electrocatalysts on super-flat indium tin oxide (ITO) substrate. NiFe hydroxide exhibited prominent OER performance, achieving an ultra-low overpotential of 236 mV at 10 mA/cm2 in alkaline solution. With the superior OER activity, we achieved an unassisted solar water splitting by series connected perovskite solar cells (PSCs) of 2 cm2 aperture area with NiFe/ITO//Pt electrodes, yielding overall solar to hydrogen (STH) efficiency of 13.75 %. Furthermore, we upscaled the monolithic facility to utilize perovskite solar module for large-scale hydrogen production and maintained an approximate operating current of 20 mA. This creative strategy contributes to the decrease of industrial manufacturing expenses for perovskite-based photovoltaic-electrochemical (PV-EC) hydrogen production, further accelerating the conversion and utilization of carbon-free energy.

Halloysite-derived hierarchical cobalt silicate hydroxide hollow nanorods assembled by nanosheets for highly efficient electrocatalytic oxygen evolution reaction

The oxygen evolution reaction (OER) is regarded as the bottleneck of electrolytic water splitting. Thus, developing robust earth-abundant electrocatalysts for efficient OER has received a great deal of attention and it is an ongoing scientific challenge. Herein, hierarchical hollow nanorods assembled with ultrathin mesoporous cobalt silicate hydroxide nanosheets (denoted as CoSi) were successfully fabricated, using the silica nanotube derived from halloysite as a sacrificial template, via a simple hydrothermal method. The resulting cobalt silicate hydroxide nanosheets stack with thicknesses ∼10 nm, as confirmed by transmission electron microscopy. The elaborated nanoarchitecture possesses a high specific surface area (SSA) allowing good exposure to the cobalt active centers exhibiting superior catalytic activity vs analogs synthesized using sodium silicate. Among all as-prepared CoSi samples, those synthesized at 150°C (CoSi-150) exhibited the minimum overpotential of ∼347 mV at a current density of 10 mA cm–2. In addition, CoSi-150 also exhibited superior performance against typical cobalt-based catalysts, and its surface hydroxyl groups were beneficial for the enhancement of OER performance. Furthermore, the CoSi-150 showed excellent durability and stability after the 105 s chronopotentiometry test in 1 M KOH. This design concept provides a new strategy for the low-cost preparation of high-quality cobalt water splitting electrocatalysts.

Covalent Transition Metal Borosilicides: Reaction Pathways in Molten Salts for Water Oxidation Electrocatalysis.

The properties of transition metal borides and silicides are intimately linked to the covalent character of the chemical bonds within their crystal structures. Bringing boron and silicon together within metal borosilicides can then engender different competing covalent networks and complex charge distributions. This situation results in unique structures and atomic environments, which can impact charge transport and catalytic properties. Metal borosilicides, however, hold the status of unusual exotic species, difficult to synthesize and with poor knowledge of their properties. Our strategy consists of developing a redox pathway to synthesize transition metal borosilicides in inorganic molten salts as high-temperature solvents. By studying the formation of Ni6Si2B, Co4.75Si2B, Fe5SiB2, and Mn5SiB2 with in situ X-ray diffraction, we highlight how new reaction routes, maintaining covalent structural building blocks, draw a general scheme of their formation. This pathway is driven by the covalence of the chemical bonds within the boron coordination framework. Next, we demonstrate high efficiency for water oxidation electrocatalysis, especially for Ni6Si2B. We ascribe the strongly increased resistance to corrosion, high stability, and electrocatalytic activity of the Ni6Si2B-derived material to three factors: (1) the two entangled boron and silicon covalent networks; (2) the ability to codope with boron and silicon an in situ generated catalytic layer; and (3) a rare electron enrichment of the transition metal by back-donation from boron atoms, previously unknown within this compound family. With this work, we then unveil a new chemical dimension for Earth-abundant water oxidation electrocatalysts by bringing to light a new family of materials.

Electrocatalytic Performance of 2D Monolayer WSeTe Janus Transition Metal Dichalcogenide for Highly Efficient H2 Evolution Reaction.

Nowadays, the development of clean and green energy sources is the priority interest of research due to increasing global energy demand and extensive usage of fossil fuels, which create pollutants. Hydrogen has the highest energy density by weight among all chemical fuels. For the commercial-scale production of hydrogen, water electrolysis is the best method, which requires an efficient, cost-effective, and earth-abundant electrocatalyst. Recent studies have shown that the 2D Janus transition metal dichalcogenides (JTMDs) are promising materials for use as electrocatalysts and are highly effective for electrocatalytic H2 evolution reaction (HER). Here, we report a 2D monolayer WSeTe JTMD, which is highly effective toward HER. We have studied the electronic properties of 2D monolayer WSeTe JTMD using the periodic hybrid DFT-D method, and a direct electronic band gap of 2.39 eV was obtained. We have explored the HER pathways, mechanisms, and intermediates, including various transition state (TS) structures (Volmer TS, i.e., H*-migration TS, Heyrovsky TS, and Tafel TS) using a molecular cluster model of the subject JTMD noted as W10Se9Te12. The present calculations reveal that the 2D monolayer WSeTe JTMD is a potential electrocatalyst for HER. It has the lowest energy barriers for all the TSs among other TMDs. It has been shown that the Heyrovsky energy barrier (= 8.72 kcal mol-1) in the case of the Volmer-Heyrovsky mechanism is larger than the Tafel energy barrier (= 3.27 kcal mol-1) in the Volmer-Tafel mechanism. Hence, our present study suggests that the formation of H2 is energetically more favorable via the Volmer-Tafel mechanism. This study helps to shed light on the rational design of 2D single-layer JTMD, which is highly effective toward HER, and we expect that the present work can be further extended to other JTMDs to find out the improved electrocatalytic performance.

Nitrogen-doped carbon confined Cr2S3 hybrid as an efficient low-cost catalyst for electrochemical ammonia synthesis under ambient condition

A chromium sulfide-based nanohybrid (NC/Cr2S3) has been fabricated by a facile strategy of pyrolysis and vulcanization of metal complex. In this nanocomposite, the in situ formed Cr2S3 nanoparticles with a mean size about ∼ 100 nm are confined by the nitrogen-doped carbon plates-derived from the metal complex. The composite is endowed with some structural advantages involving extended surface areas, increased catalytically active centers and enhanced conductivity. As an earth-abundant low-cost electrocatalyst for nitrogen reduction reaction (NRR), compared with bare Cr2S3, NC/Cr2S3 hybrid delivers a boosted and stable catalytic activity for NRR at a low potential under mild conditions. NC/Cr2S3 is able to exhibit a high ammonia yield rate of 30.33 μg mg-1cat h−1 at −0.4 V vs RHE in sodium sulfate solution with a Faradic efficiency up to 7.66 %. Moreover, no hydrazine byproduct can be detected, showcasing a satisfactory selectivity.

Rational Construction of a 3D Self-Supported Electrode Based on ZIF-67 and Amorphous NiCoP for an Enhanced Oxygen Evolution Reaction.

The development of efficient and Earth-abundant electrocatalysts for the oxygen evolution reaction (OER) is an urgent requirement in the field of electrochemical water splitting. The electrocatalytic performance of the OER can be greatly enhanced by the synergistic combination of zeolite imidazolate frameworks (ZIFs) and transition-metal phosphides, both of which individually exhibit promising capabilities in this regard. In this study, a novel amorphous NiCoP deposited on ZIF-67 sheets supported on Ni foam (labeled as NiCoP/ZIF-67/NF) as an OER electrocatalytic material was successfully synthesized using a simple, secure, and time-efficient two-step strategy. The experimental results demonstrate that NiCoP/ZIF-67/NF possesses a large active surface area with abundant active sites. Also, the synergistic effect and interaction between NiCoP and ZIF-67, as well as between Ni and Co within NiCoP, effectively enhance its electrochemical performance under alkaline conditions. Consequently, NiCoP/ZIF-67/NF exhibits outstanding catalytic activity for OER with an overpotential (η) of 175 mV at a current density of 10 mA cm-2 and a long-term stability over 40 h at 20 mA cm-2 in a 1.0 M KOH electrolyte. The corresponding analyses suggest that the real active sites responsible for the OER are identified as NiOOH and CoOOH species within the structure of NiCoP/ZIF-67/NF. Additionally, the catalytic function and stability of ZIF-67 toward the OER under alkaline conditions were also briefly discussed. This work provides a novel catalytic material for the OER along with a facile strategy to fabricate superior, efficient, and noble metal-free catalysts suitable for energy-related applications.

Structural Aspects of MoS x Prepared by Atomic Layer Deposition for Hydrogen Evolution Reaction.

Molybdenum sulfides (MoS x ) in both crystalline and amorphous forms are promising earth-abundant electrocatalysts for hydrogen evolution reaction (HER) in acid. Plasma-enhanced atomic layer deposition was used to prepare thin films of both amorphous MoS x with adjustable S/Mo ratio (2.8-4.7) and crystalline MoS2 with tailored crystallinity, morphology, and electrical properties. All the amorphous MoS x films transform into highly HER-active amorphous MoS2 (overpotential 210-250 mV at 10 mA/cm2 in 0.5 M H2SO4) after electrochemical activation at approximately -0.3 V vs reversible hydrogen electrode. However, the initial film stoichiometry affects the structure and consequently the HER activity and stability. The material changes occurring during activation are studied using ex situ and quasi in situ X-ray photoelectron spectroscopy. Possible structures of as-deposited and activated catalysts are proposed. In contrast to amorphous MoS x , no changes in the structure of crystalline MoS2 catalysts are observed. The overpotentials of the crystalline films range from 300 to 520 mV at 10 mA/cm2, being the lowest for the most defective catalysts. This work provides a practical method for deposition of tailored MoS x HER electrocatalysts as well as new insights into their activity and structure.

Three-dimensional interconnected nanofibers consisting of ultra-small Ni-doped Co3O4 nanoparticles for acidic overall water splitting at high current density

Exploring earth-abundant electrocatalysts to replace platinum/iridium for acidic overall water splitting at high current density is an important challenge towards lowering the cost of green hydrogen production. Herein, we developed a new class of three-dimensional interconnected nanofibers (NFs) composed of ultra-small Ni-doped Co3O4 nanoparticles (Ni-Co3O4 NFs). Benefiting from the unique ultra-small Ni-doped Co3O4 composition and three-dimensional interconnected porous structure, 13.4 % Ni-Co3O4 NFs (Ni doping is 13.4 wt%) exhibits remarkable electrocatalytic performance in acidic media. Specially, in strongly acidic environments, high activity and high stability overall water splitting can be achieved at high current density. As evidenced by the fact that a voltage of 500 mA cm−2 can be achieved at only 1.86 V and operational stability can be maintained at 500 mA cm−2 for 100 h.

Modification of NiSe2 Nanoparticles by ZIF-8-Derived NC for Boosting H2O2 Production from Electrochemical Oxygen Reduction in Acidic Media

The two-electron oxygen reduction reaction (2e− ORR) has emerged as an attractive alternative for H2O2 production. Developing efficient earth-abundant transition metal electrocatalysts and reaction mechanism exploration for H2O2 production are important but remain challenging. Herein, a nitrogen-doped carbon-coated NiSe2 (NiSe2@NC) electrocatalyst was prepared by successive annealing treatment. Benefiting from the synergistic effect between the NiSe2 nanoparticles and NC, the 2e− ORR activity, selectivity, and stability of NiSe2@NC in 0.1 M HClO4 was greatly enhanced, with the yield of H2O2 being 4.4 times that of the bare NiSe2 nanoparticles. The in situ Raman spectra and density functional theory (DFT) calculation revealed that the presence of NC was beneficial for regulating the electronic state of NiSe2 and optimizing the adsorption free energy of *OOH, which could enhance the adsorption of O2, stabilize the O-O bond, and boost the production of H2O2. This work provides an effective strategy to improve the performance of the transition metal chalcogenide for 2e− ORR to H2O2.

Nanoengineered Cobalt Electrocatalyst for Alkaline Oxygen Evolution Reaction.

The alkaline oxygen evolution reaction (OER) remains a bottleneck in green hydrogen production owing to its slow reaction kinetics and low catalytic efficiencies of earth abundant electrocatalysts in the alkaline OER reaction. This study investigates the OER performance of hierarchically porous cobalt electrocatalysts synthesized using the dynamic hydrogen bubble templating (DHBT) method. Characterization studies revealed that electrocatalysts synthesized under optimized conditions using the DHBT method consisted of cobalt nanosheets, and hierarchical porosity with macropores distributed in a honeycomb network and mesopores distributed between cobalt nanosheets. Moreover, X-ray photoelectron spectroscopy studies revealed the presence of Co(OH)2 as the predominant surface cobalt species while Raman studies revealed the presence of the cubic Co3O4 phase in the synthesized electrocatalysts. The best performing electrocatalyst required only 360 mV of overpotential to initiate a current density of 10 mA cm-2, exhibited a Tafel slope of 37 mV dec-1, and stable OER activity over 24 h. The DHBT method offers a facile, low cost and rapid synthesis approach for preparation for highly efficient cobalt electrocatalysts.

Lattice-matched spinel/layered double hydroxide 2D/2D heterojunction towards large-current-density overall water splitting

It is fascinating and challenging to construct earth-abundant first-row transition metal-based bifunctional electrocatalysts for large-scale hydrogen production via water electrolysis. Here we report a progressive conversion from spinel nanosheets to layered double hydroxide (LDH) nanosheets through the preferential dissolution of alternated layers in spinel. This process enables the formation of a lattice-matched and chemically bonded edge-to-edge spinel/LDH 2D/2D heterojunction. Significant charge redistribution at the 2D/2D heterointerface accelerates water dissociation kinetics and optimize adsorption energy of hydrogen- and oxygen-containing intermediates. The synthesized CoFe2O4/CoFe-LDH 2D/2D heterojunction demonstrates exceptional performance in the hydrogen evolution reaction, achieving an overpotential of 337 mV at a high current density of 1000 mA cm−2, surpassing previously reported non-noble metal-based spinels and LDHs. Furthermore, its oxygen evolution reaction performance is comparable to that of typical spinel and LDH catalysts. The in-depth insights can guide rational interfacial engineering of heterogeneous catalysts for energy and environmental applications.

Interface engineering of 2D NiFe LDH/NiFeS heterostructure for highly efficient 5-hydroxymethylfurfural electrooxidation

The electrochemical oxidation of 5-hydroxymethylfurfural (HMF) to valuable chemicals is an efficient way to upgrade biomass molecules and replace traditional catalytic synthesis. It is crucial to develop efficient and low-cost earth-abundant electrocatalysts to enhance catalytic performance of HMF oxidation. Herein, a new type of two-dimensional (2D) hybrid arrays consisting of NiFe layered double hydroxides (LDH) nanosheets and bimetallic sulfide (NiFeS) is constructed via interface engineering for efficient electrocatalytic oxidation of HMF to 2,5-furandicarboxylic acid (FDCA). The preparation process of 2D NiFe LDH/NiFeS with ultrathin heterostructure involves in anchoring a Co-based metal-organic framework (Co MOF) as template onto the carbon cloth (CC) via in-situ growth, formation of NiFe LDH on the surface of Co MOF and subsequent partial sulfidation. The electrocatalyst of NiFe LDH/NiFeS exhibits outstanding performance towards HMF oxidation, about 98.5% yield for FDCA and 97.2% Faraday efficiency (FE) in the alkaline electrolyte with 10 mmol/L HMF, as well as excellent stability retaining 90.1% FE for FDCA after six cycles test. Moreover, even at an HMF concentration of 100 mmol/L, the yield and FE for FDCA remain high at 83.6% and 93.6%, respectively. These findings highlight that 2D heterostructure containing abundant interfaces between NiFe LDH nanosheets and NiFeS can enhance the intrinsic activity of LDH and thus promote the oxidation reaction kinetics. Additionally, the synergistic effect of the bimetallic NiFe compounds also improved the selectivity of HMF conversion to FDCA. Our present work demonstrates that constructing 2D ultrathin heterostructure of NiFe LDH/NiFeS is a facile strategy via interface engineering to enhance the intrinsic activity of LDH electrocatalysts, which would open new avenues toward low-cost and advanced 2D nanocatalysts for sustainable energy conversion and electrochemical valorization of biomass derivatives.