Oxygen Evolution Reaction In Alkaline Media Research Articles

Multiwall carbon nanotubes supported rhenium doped Co3O4 as an efficient electrocatalyst for water oxidation in alkaline medium

The recent trends for the development of efficient and low cost transition metal (TMs) based anode catalysts for water splitting is crucial and important. Even though, research is continuously progressing in different directions to design catalyst; however, catalytic OER (oxygen evolution reaction) activity has remained insufficient. Till now, various transition metal oxides (TMOs) have been used as efficient and cost-effective electrocatalyst for the oxygen evolution reaction. The catalytic performance of TMOs could be enhanced by doping with the metal, which increases the catalyst's charge transfer and electronic conductivity. Decoration of TMOs with the multi-wall carbon nanotube (MWCNT) further improves catalytic activity by providing numerous active sites. Here, Co3O4/MWCNT and Rhenium (Re) doped Co3O4/MWCNT composite were prepared by simple hydrothermal process and used as electrocatalyst for OER in alkaline medium. Different concentrations of Re (0.05 mmol, 0.1 mmol, 0.2 mmol, 0.3 mmol) were doped and it was observed that the electrochemical results of the 0.2 mmol Re doped Co3O4/ MWCNT (R0.2CO) was most efficient electrocatalyst which offers the OER overpotential of 298 mV/dec to attain the 10 mA cm−2 current density, lower Tafel slope (70 mV/dec), higher value of turn over frequency (0.95), lower value of the charge transfer resistance (3.10Ω) and good stability, demonstrating the better OER catalytic activity as compared to un-doped Co3O4/MWCNT (R0.0CO) catalyst. The investigated catalyst R0.2CO is more efficient catalyst than most of the reported similar type of catalysts and offers comparable electrocatalytic activity with benchmark electrocatalyst RuO2.

Construction of heterogeneous interfaces for water activation and dissociation to synergistically boost overall water splitting

Construction of heterogeneous interfaces with dual active components to synergistically promote both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is an effective strategy for facilitating electrochemical water splitting, but the appropriate active component regulation via simple synthesis procedures is still challenging. Herein, the Co and Co2Mo3O8 active components are screened to construct effective heterogeneous interfaces and successfully integrated on Ni foam by thermal reduction of cobalt molybdate precursor. And this bifunctional electrode (Co/Co2Mo3O8/NF) required overpotentials of only 164 and 360 mV to drive the 100 mA cm−2 for HER and OER in alkaline media, respectively. Theoretical calculations showed that the electron transfer occurred from Co to Co2Mo3O8 at the interface, then the formed interfacial cobalt atoms with deficient electron were beneficial for water activation, and reduced energy barrier of water dissociation under the synergistic effect of Co2Mo3O8. Notably, the alkaline electrolyzer based on symmetric Co/Co2Mo3O8/NF electrodes generated 100 mA cm−2 at a voltage of only 1.75 V, surpassing commercially available precious-metal Pt/RuO2-based catalysts.

Room‐Temperature, Meter‐Scale Synthesis of Heazlewoodite‐Based Nanoarray Electrodes for Alkaline Water Electrolysis

AbstractAlkaline water electrolysis is among the most promising technologies to massively produce green hydrogen. Developing highly‐active and durable electrodes to catalyze the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) is of primary importance. Here a facile, room‐temperature synthetic route is presented to access heazlewoodite phase (Ni, Fe)3S2 nanosheet arrays supported on NiFe foam (NFF), whose production can be easily scaled up to meter size per batch operation. The (Ni, Fe)3S2/NFF electrode can serve as a high‐performance electrocatalyst for both HER and OER in alkaline media, and remains highly stable for over 1000 h at 100 mA cm−2 current densities. When working as HER electrocatalyst, (Ni, Fe)3S2 is confirmed as catalytic phase that provides a high density of efficient active sites (e.g., Ni─Ni and Ni─Fe bridge sites). During electrochemical OER testing, (Ni, Fe)3S2 nanosheets totally transform into γ‐(Fe, Ni)OOH as active catalytic phase for OER. As a consequence, the (Ni, Fe)3S2/NFF can be used to integrate into an alkaline electrolyzer as both the cathode and anode, and to give an excellent catalytic performance (600 mA cm−2 @1.93 V), which is better than the alkaline electrolyzer based on commercial Raney Ni electrodes.

Ru nanoparticles modified Ni3Se4/Ni(OH)2 heterostructure nanosheets: A fast kinetics boosted bifunctional overall water splitting electrocatalyst

Properly design and manufacture of bifunctional electrocatalysts with superb performance and endurance are crucial for overall water splitting. The interfacial engineering strategy is acknowledged as a promising approach to enhance catalytic performance of overall water splitting catalysts. Herein, the Ru nanoparticles modified Ni3Se4/Ni(OH)2 heterostructured nanosheets catalyst was constructed using a simple two-step hydrothermal process. The experimental results demonstrate that the abundant heterointerfaces between Ru and Ni3Se4/Ni(OH)2 can increase the number of active sites and effectively regulate the electronic structure, greatly accelerating the kinetics of the hydrogen evolution reaction (HER)/oxygen evolution reaction (OER). As a result, the Ru/Ni3Se4/Ni(OH)2/NF catalyst exhibits the low overpotential of 102.8 mV and 334.5 mV at 100 mA cm−2 for HER and OER in alkaline medium, respectively. Furthermore, a two-electrode system composed of the Ru/Ni3Se4/Ni(OH)2/NF requires a battery voltage of just 1.51 V at 10 mA cm−2 and remains stable for 200 h at 500 mA cm−2. This work provides an effective strategy for constructing Ru-based heterostructured catalysts with excellent catalytic activity.

The oxygen path mechanism from Ni-OOOO-Fe species in oxygen evolution reaction on NiFe layered double hydroxides

The oxygen evolution reaction (OER) with large overpotential is the bottleneck of the whole water electrolysis process. NiFe layered double hydroxide (NiFe-LDH) represent one of the potential catalysts for OER in alkaline media. For the LDH, it was well established that both adsorption evolution mechanism and lattice oxygen mechanism could appear at a single site, but Ni-OOOO-Fe species would provide a different OO path mechanism at dual-O sites due to the complexity and diversity of LDH surface. Here, using first-principles study, tetra-oxygen path mechanism (t-OPM) was proposed to investigate the OER performance of NiFe-LDH by considering surface 2O were as active sites (Oac) and other O as environment O (Oev) with different exposed degrees (0–6). It was found that the optimal performance of the NiFe-LDH surface could be achieved when 2 ∼ 4 Oev were exposed under the explored mechanism in different paths (path 1 and path 2) with overpotential η = 0.07 ∼ 0.35 V, and path 1 was slightly better than path 2. At the same time, the solvation effect (SE) was used to study the effect on the OER performance, the results showed that SE had a little influence on the case of 2 ∼ 4 Oev exposed while had a large effect on the other cases. The detailed analysis of the electronic structure showed a smaller difference Δε between the energy Fe-3d band center and Oac-2p, which imply the stronger the interaction between them. Thus, the t-OPM was feasible in OER on NiFe-LDH. It was anticipated that our work could provide a fresh perspective on the understanding of the excellent OER performance of LDH in alkaline environment, which was complementary to the traditional mechanism to some extent.

Boosting oxygen evolution reaction rates with mesoporous Fe-doped MoCo-phosphide nanosheets.

Transition metal-based catalysts are commonly used for water electrolysis and cost-effective hydrogen fuel production due to their exceptional electrochemical performance, particularly in enhancing the efficiency of the oxygen evolution reaction (OER) at the anode. In this study, a novel approach was developed for the preparation of catalysts with abundant active sites and defects. The MoCoFe-phosphide catalyst nanosheets were synthesized using a simple one-step hydrothermal reaction and chemical vapor deposition-based phosphorization. The resulting MoCoFe-phosphide catalyst nanosheets displayed excellent electrical conductivity and a high number of electrochemically active sites, leading to high electrocatalytic activities and efficient kinetics for the OER. The MoCoFe-phosphide catalyst nanosheets demonstrated remarkable catalytic activity, achieving a low overpotential of only 250 mV to achieve the OER at a current density of 10 mA cm-2. The catalyst also exhibited a low Tafel slope of 43.38 mV dec-1 and maintained high stability for OER in alkaline media, surpassing the performance of most other transition metal-based electrocatalysts. The outstanding OER performance can be attributed to the effects of Mo and Fe, which modulate the electronic properties and structures of CoP. The results showed a surface with abundant defects and active sites with a higher proportion of Co2+ active sites, a larger specific surface area, and improved interfacial charge transfer. X-ray photoelectron spectroscopy (XPS) analysis revealed that the catalyst's high activity originates from the presence of Mo6+/Mo4+ and Co2+/Co3+ redox couples, as well as the formation of active metal (oxy)hydroxide species on its surface.

N/P-doped NiFeV oxide nanosheets with oxygen vacancies as an efficient electrocatalyst for the oxygen evolution reaction.

Plasma treatment as an effective strategy can simultaneously achieve surface modification and heteroatom doping. Here, an N/P-doped NiFeV oxide nanosheet catalyst (N/P-NiFeVO) constructed by Ar/PH3 plasma treatment is used to drive the oxygen evolution reaction (OER). The introduction of V species leads to the formation of an ultrathin ordered nanostructure and exposure of more active sites. Compared to the 2D NiFeV LDH, the prepared N/P-NiFeVO by plasma treatment possesses multiple-valence Fe, V and Ni species, which regulate the intrinsic electronic structure and enable a superior catalytic activity for the OER in alkaline media. Specifically, the N/P-NiFeVO only require an overpotential of 273 mV to drive the current density of 100 mA cm-2. What's more, the electrode can maintain a stable current density in a long-term oxygen evolution reaction (∼120 h) under alkaline conditions. This work provides new insight for the rational design of mixed metal oxides for OER electrocatalysts.

Transition metal-based electrocatalysts for alkaline overall water splitting: advancements, challenges, and perspectives.

Water electrolysis is a promising method for efficiently producing hydrogen and oxygen, crucial for renewable energy conversion and fuel cell technologies. The hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are two key electrocatalytic reactions occurring during water splitting, necessitating the development of active, stable, and low-cost electrocatalysts. Transition metal (TM)-based electrocatalysts, spanning noble metals and TM oxides, phosphides, nitrides, carbides, borides, chalcogenides, and dichalcogenides, have garnered significant attention due to their outstanding characteristics, including high electronic conductivity, tunable valence electron configuration, high stability, and cost-effectiveness. This timely review discusses developments in TM-based electrocatalysts for the HER and OER in alkaline media in the last 10 years, revealing that the exposure of more accessible surface-active sites, specific electronic effects, and string effects are essential for the development of efficient electrocatalysts towards electrochemical water splitting application. This comprehensive review serves as a guide for designing and constructing state-of-the-art, high-performance bifunctional electrocatalysts based on TMs, particularly for applications in water splitting.

Cobalt–organic framework as a Bi–functional electrocatalyst for renewable hydrogen production by electrochemical water splitting

Sustainable hydrogen production by electrocatalytic water splitting is an attractive approach to establish a carbon–free future. On the other hand, the operationalization of this technology on a large scale requires the design and synthesis of efficient electrocatalysts to promote hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Metal–organic frameworks (MOFs) have provided new opportunities in the field of electrocatalytic water splitting due to their unique properties. Herein, we report an affordable, simple, and environmentally friendly strategy for the synthesis of Co3(BTC)2 MOF electrocatalyst in distilled water at room temperature. Surprisingly, Co3(BTC)2 demonstrated superior electrocatalytic activity toward HER and OER in alkaline media. The Co3(BTC)2 requires overpotentials of 450 and 370mV for HER and OER to achieve a current density of 10mA cm−2, respectively.

NiFe codoping-regulated amorphous/crystalline heterostructured Co-based hydroxides/tungstate with rich oxygen vacancies for efficient water oxidation catalysis

Oxygen evolution reaction (OER) is a crucial half-reaction in water splitting, generating hydrogen for sustainable development, but it is often subject to sluggish kinetics. Abundant transition metal-based OER electrocatalysts have been utilized to expedite the process. However, traditional amorphous catalysts suffer from low conductivity, while the activity of crystalline catalysts is also unsatisfactory. Herein, an amorphous/crystalline heterostructured Co-based hydroxide/tungstate was meticulously constructed and further tailored using a NiFe codoping method (NiFeCoW). Following NiFe codoping, the electronic structure had been modulated, subsequently altering the adsorption toward intermediates. From the electrochemical measurements, the NiFeCoW catalyst demonstrated superior electrocatalytic activity for OER in alkaline media, with a minimal overpotential of 297 mV at 10 mA cm−2 and a cell voltage of 1.57 V for water splitting. This study provides valuable guidance for regulating the amorphous/crystalline heterophase in catalysts through bimetallic modulating engineering.

Insights into the Structure Sensitivity of Fe-Based Materials for the Oxygen Evolution Reaction

The conversion of renewable energy into storable fuels is fundamental to the meeting of the net-zero CO2 emissions objective by 2050. However, the sluggish kinetics of the oxygen evolution reaction (OER) and the poor stability of electrocatalysts at industrial-level currents remain a problem for electrolyzers 1. Using platinum group metal-free electrocatalysts in anion exchange membrane electrolyzers is an appealing strategy to overcome some of the problems associated with PEM electrolyzers. Fe-based materials offer the possibility for the development of active, stable, and cost-effective electrocatalysts for the OER in alkaline media.In this work, we explore the influence of structure, composition, or crystalline phase on different Fe-based electrodes for the OER. Different fabrication procedures such as additive manufacturing 2, flame spray synthesis, or pulse laser ablation 3 allow us to have a wide range of Fe-based materials with a well-defined structure/composition/phase. The materials have been extensively characterized by physicochemical methods (XPS, Raman, XRD, ICP) and their electrocatalytic activity evaluates following careful procedures in order to obtain reliable results. The results show that the activity of Fe-rich electrodes is poor. However, if Fe is alloyed with other materials or its surface structure or crystallinity degree is modified, it results in a more active material. This information could guide the synthesis of more active and stable water-splitting materials. References S. Cherevko, S. Geiger, O. Kasian, N. Kulyk, J.-P. Grote, A. Savan, B. R. Shrestha, S. Merzlikin, B. Breitbach, A. Ludwig, and K. J. J. Mayrhofer, Catalysis Today, 262 170-180 (2016). J. Wegner, R. Martínez-Hincapié, V. Čolić, and S. Kleszczynski, Advanced Materials Interfaces, n/a (n/a), 2202499 (2023). J. Johny, Y. Li, M. Kamp, O. Prymak, S.-X. Liang, T. Krekeler, M. Ritter, L. Kienle, C. Rehbock, S. Barcikowski, and S. Reichenberger, Nano Research, 15 (6), 4807-4819 (2022).

LiMn2O4 as a Model System to Understand the Mn Dissolution Mechanism during Water Oxidation

LiMn2O4 as a model system to understand the Mn dissolution mechanism during water oxidation Omeshwari Bisen1,2, M. Baumung1,2, F. Schönewald2, C. A. Volkert2, M. Risch1,2 1 Nachwuchsgruppe Gestaltung des Sauerstoffentwicklungsmechanismus, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1,14109 Berlin, Germany 2 Institut für Materialphysik, Georg-August-Universität Göttingen, Germany Email: omeshwari.bisen@helmholtz-berlin.de The water splitting provides an attractive avenue for chemical energy storage by producing the green hydrogen, but it suffers from the inefficiency of the oxygen evolution reaction (OER) and the degradation of the electrocatalyst under the harsh oxidizing conditions of the reaction. Manganese oxides are attractive due to their abundance and as a non-critical raw material, but they are known to degrade quickly during the OER, which hinders their usage severely. [1] Therefore, it is equivalently important to focus on the understanding of degradation processes during the OER. [2]In this study and our previous studies, we used the battery material LiMn2O4 as a model system for the OER in alkaline media where the Mn valence can be tuned with little effect on structure. [3, 4] LiMn2O4 exhibits a core-shell cubic-spinel structure with tetrahedral antisite Mn2+ defects in the shell. [5] We have used the rotating ring-disk electrode (RRDE) setup to obtain the product current of manganese corrosion and oxygen evolution by applying the desired potential at the Pt ring (Fig. 1a). We monitored the dissolution of Mn from the LiMn2O4 (Fig. 1b) and found two onsets of exponential currents, indicating the two distinct Mn loss processes; one independent of the OER and one associated to it, which is further investigated by Tafel slopes. The ex-situ X-ray absorption spectroscopy (Fig. 1c) and X-ray photoelectron spectroscopy (Fig. 1d) represents the oxidation of Mn moieties after voltage cycling including the OER, and loss of Mn2+ and Li+. We correlate near-surface oxidation with the charge attributed to dissolved Mn, which demonstrates increasing Mn dissolution with the formation of surface Mn4+ species under anodic potential and observed the distinct atomistic origin before and after OER onset.[6] It is highly desirable to understand the atomistic insights into the Mn dissolution processes for the knowledge-guided mitigation of electrocatalyst degradation during water oxidation, which can be broadly extended to manganese-based oxide systems.

Electrochemical oxygen generation from VO2 nanoflakes decorated onto graphite sheet

The present study deals with the synthesis of VO2 anchored across graphite sheets using a carbothermal reduction technique. The phase identification, elemental, and morphology of the obtained VO2/graphite heterostructure were examined using analytical techniques. Morphological characterization by FESEM confirms the formation of nanoflakes like the structure of VO2/graphite heterostructure. The sample obtained was drop cast onto graphite and the material was utilized as a working electrode for the electrochemical oxygen evolution reaction (OER). The VO2/graphite heterostructure shows an overpotential of 470 mV as compared to V2O5/graphite, which has an overpotential of 800 mV during OER in alkaline media. Additionally, the VO2/graphite electrocatalyst exhibits a low charge transfer resistance of 29.5 Ω and a low Tafel slope value corresponding to 85 mV dec−1. The results signify that the VO2/graphite heterostructure has emerged as an efficient catalytic material for OER application. Therefore, the present work focuses on the simpler method for the synthesis of VO2/graphite heterostructure with long-term performance during O2 evolution and also renders the potential catalytic applications of vanadium-based metal oxide.

Surface-Modified Carbon Nanotubes with Ultrathin Co3O4 Layer for Enhanced Oxygen Evolution Reaction.

Alkaline water electrolysis is a vital technology for sustainable and efficient hydrogen production. However, the oxygen evolution reaction (OER) at the anode suffers from sluggish kinetics, requiring overpotential. Precious metal-based electrocatalysts are commonly used but face limitations in cost and availability. Carbon nanostructures, such as carbon nanotubes (CNTs), offer promising alternatives due to their abundant active sites and efficient charge-transfer properties. Surface modification of CNTs through techniques such as pulsed laser ablation in liquid media (PLAL) can enhance their catalytic performance. In this study, we investigate the role of surface-modified carbon (SMC) as a support to increase the active sites of transition metal-based electrocatalysts and its impact on electrocatalytic performance for the OER. We focus on Co3O4@SMC heterostructures, where an ultrathin layer of Co3O4 is deposited onto SMCs using a combination of PLAL and atomic layer deposition. A comparative analysis with aggregated Co3O4 and Co3O4@pristine CNTs reveals the superior OER performance of Co3O4@SMC. The optimized Co3O4@SMC exhibits a 25.6% reduction in overpotential, a lower Tafel slope, and a significantly higher turnover frequency (TOF) in alkaline water splitting. The experimental results, combined with density functional theory (DFT) calculations, indicate that these improvements can be attributed to the high electrocatalytic activity of Co3O4 as active sites achieved through the homogeneous distribution on SMCs. The experimental methodology, morphology, composition, and their correlation with activity and stability of Co3O4@SMC for the OER in alkaline media are discussed in detail. This study contributes to the understanding of SMC-based heterostructures and their potential for enhancing electrocatalytic performance in alkaline water electrolysis.

Substrate-Driven Electrocatalysis of Natural and Earth-Abundant Pyrite Towards Oxygen Evolution Reaction

The fabrication of an economical, earth-abundant, environment-friendly, and highly efficient electrocatalyst for anodic oxygen evolution reaction (OER) in the electrolysis of water is essential for sustainable energy conversion and storage technology. Among the various transition metal-based electrocatalysts, iron-based electrocatalysts are well-known for their catalytic behavior due to their effective redox activity, abundance, and low toxicity. Pyrites are the most prevalent Fe-containing minerals in the earth's crust, but their use as an electrocatalyst for oxygen evolution reaction (OER) has received little attention though their synthetic counterparts have shown better activity. Herein, the naturally occurring pyrite (FeS2) on Ni foam is evaluated as a dynamic electrocatalyst towards OER in alkaline media. Various spectro-analytical techniques have been used to confirm the chemical and physical characteristics of earth abundant pyrite. The pyrite-coated nickel foam exhibited an extraordinarily superior catalytic activity for OER with overpotential of 203 and 315 mV at current densities of 10 mA∙cm−2 and 50 mA∙cm−2, respectively in 1.0 M potassium hydroxide (KOH) electrolyte at a scan rate of 5 mV∙s−1. Meanwhile, the benchmark precious iridium oxide (IrO2) on nickel foam demonstrated an overpotential of 322 and 430 mV for OER at 10 and 50 mA∙cm−2, respectively. It's important to note that the catalyst used is a natural pyrite with some additional constituents in small quantities. Therefore, the analysis revealed the presence of carbon (C), silicon (Si) and oxygen (O) in addition to FeS2. This composition, along with the synergistic behavior of nickel ions from the nickel foam, likely contributes to the enhancement in catalytic activity observed. The pyrite on carbon substrate, did not exhibit the same impressive OER activity as like on Ni foam, emphasizing the significance of the substrate-dependent performance. Nevertheless, on the nickel foam, natural pyrite displayed the lowest overpotential, Tafel slope, and better stability for OER. Hence, on Ni foam substrate, earth-abundant, low-cost, stable, and efficient pyrite-based catalyst augmented by synergistic interactions with nickel ions, may hold great promise for advancing the field of water electrolysis and facilitating cleaner energy production and conversion.

MOF-templated CuO and Mn[sbnd]CuO/Cu2O composites as electrocatalyst in oxygen evolution

Considering the great need for the development of new electrocatalysts for oxygen evolution reaction (OER), this work reports the synthesis and characterization of four new copper-based electrocatalysts derived from metal–organic frameworks (MOFs). Homometallic (CuIDA, [Cu(IDA)(H2O)2]n IDA= iminodiacetate) and heterobimetallic [Cu0.902Mn0.096(IDA)(H2O)2]n, [Cu0.703Mn0.297(IDA)(H2O)2]n and [Cu0.487Mn0.513(IDA)(H2O)2]n MOFs were obtained by precipitation method and characterized by X-ray diffraction (XRD) with Rietveld refinement, infrared spectroscopy (FT-IR) and thermogravimetric (TGA). The calcination of CuIDA and heterobimetallic MOFs under air atmosphere led to the formation of CuO and CuO/Cu2O/Mn-x (x = 10 %, 20 % and 50 % of Mn) electrocatalyst, respectively. These materials were characterized by XRD, FT-IR, Raman spectroscopy, UV–vis spectroscopy and scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS), confirming the chemical composition and crystal structure. Copper oxide-based materials were applied as electrocatalyst for OER in alkaline medium, with overpotential of 359 mV (CuO), 355 mV (CuO/Cu2O/Mn10), 360 mV (CuO/Cu2O/Mn30) and 355 mV (CuO/Cu2O/Mn50) to record a current density of J = 10 mA cm−2. Tafel slope values indicate the adsorption of intermediate species as the rate-determining step for all electrocatalysts. These results are similar or superior to those found in the literature so far.

Quench-induced surface engineering of NiO/NiSex hybrid for highly enhanced electrochemical oxygen evolution reaction

To achieve sustainable production of hydrogen fuel through electrochemical water splitting, efficient and low-cost electrocatalysts for the kinetically sluggish oxygen evolution reaction (OER) are urgently desirable. Herein, a calcination-quenching strategy to synthesize core-shell NiO@NiSex nanorods (NiSex is the core and NiO is the shell) with tailored surface compositions and structures is reported. In the calcination step, a NiO@NiSex nanostructure supported on nickel foam (NF) (denoted as NiO@NiSex/NF) was formed via oxidative calcination of highly conductive NiSe in situ grown on NF (denoted as NiSe/NF). Subsequently, the as-obtained NiO@NiSex/NF electrode at the high temperature state was rapidly placed in a cold iron salt solution to achieve the quenching process. The results conclusively demonstrated that the quenching process resulted in iron doping and vacancies generation on the surface of NiO, effectively reconfiguring the desired surface of the catalyst, thus giving rise to notably enhanced electrocatalytic performance for OER in alkaline media. As a result, the quenched-engineered NiO@NiSex/NF electrode requires ultralow overpotentials of 231 and 265 mV to yield current densities of 10 and 100 mA cm−2, respectively, and presents a very low Tafel slope of 28.9 mV dec−1 as well as excellent durability, with the performance superior to most of metal oxide catalysts reported to date. This work extends the use of quenching chemistry in fabrication of high-performance metal oxide catalysts for energy related applications.

Spinel‐Structured High‐Entropy Oxide Nanofibers as Electrocatalysts for Oxygen Evolution in Alkaline Solution: Effect of Metal Combination and Calcination Temperature

AbstractDefect‐engineering is a viable strategy to improve the activity of nanocatalysts for the oxygen evolution reaction (OER), whose slow kinetics still strongly limits the broad market penetration of electrochemical water splitting as a sustainable technology for large‐scale hydrogen production. High‐entropy spinel oxides (HESOs) are in focus due to their great potential as low‐cost OER electrocatalysts. In this work, electrospun HESO nanofibers (NFs), based on (Cr,Mn,Fe,Co,Ni), (Cr,Mn,Fe,Co,Zn) and (Cr,Mn,Fe,Ni,Zn) combinations, with granular architecture and oxygen‐deficient surface are produced by calcination at low temperature (600 or 500 °C), characterized by a combination of benchtop analytical techniques and evaluated as electrocatalysts for OER in alkaline medium. The variation of HESO composition and calcination temperature produces complex and interdependent changes in the morphology of the fibers, crystallinity and inversion degree of the spinel oxide, concentration of the oxygen‐vacancies, cation distribution in the lattice, which mirror on different electrochemical properties of the fibers. The best electrocatalytic performance (overpotential and Tafel slope at 10 mA cm−2: 360 mV and 41 mV dec−1, respectively) pertains to (Cr1/5Mn1/5Fe1/5Co1/5Ni1/5)3O4 NFs calcined at 500 °C and results from the lower outer 3d‐electron number, eg filling closer to its optimal value and higher occupation of 16d sites by the most redox‐active species.

High-value utilization of Cr-containing sludge: Eco-friendly and ultra-low-cost electrocatalyst for efficient OER in alkaline media from Cr-containing sludge

Economically sustainable development requires more viable waste recycling solutions. In this context, we address the problem of utilizing chromium-containing sludge, a prevalent and environmentally hazardous waste. Meanwhile, sustainable energy development must develop ecology-friendly and low-cost electrocatalysts for the oxygen evolution reaction (OER) in alkaline media. Herein, we report an ultra-low-cost electrocatalyst from chromium-containing sludge. The optimum preparation conditions are determined by optimizing the calcination temperature and the loading of nickel acetylacetonate. The optimized catalyst delivers excellent stability and outstanding OER activity with overpotentials of 320 mV at 10 mA cm−2 in alkaline media. Density functional theory calculations reveal that the energy barrier of OER is decreased because of the catalyst's heterogeneous structure arrangement and confirm the influence of chromium on performance improvement. The concept of “turning waste into treasure” stimulates the search for methods to process Cr-containing waste and produce low-cost, high-performance electrocatalysts.

Scalable synthesis of MOF-derived Nd2O3@C and V2O5@C nanohybrid: Efficient electrocatalyst for OER in alkaline medium

Craving to search for renewable energy reservoirs for the development of green and robust electrocatalysts, now become essential for catalytic performance by using energy conversion devices. Herein, we fabricated a metal–organic framework (MOF) derived transition metal and rare earth metal oxides-based materials for water electrocatalysis. MOF is regarded as the potential hotspot to increase catalytic activity through fascinating chemical and structural traits. This study summarizes the oxygen evolution reaction (OER) of MOF-derived Nd2O3@C and V2O5@C by depositing them on stainless steel substrate (SS) in an alkaline medium. The grown electrocatalysts Nd2O3, V2O5, Nd-MOF, V-MOF, and MOF-derived Nd2O3@C and V2O5@C probed by various useful techniques to confirm oxidation states, phase-changing, structural, morphological, and compositional properties. The MOF-derived Nd2O3@C and V2O5@C formed irregular spherical shaped and nanorod-like morphology, respectively, which proved helpful for the easy transfer of electrons to enhance OER. The electrochemical study indicates that among all electrocatalysts, the V2O5@C electrode exhibits remarkable electrochemical results having low overpotential (282 mV), and smaller Tafel slope of 60 mVdec-1 at a current density of 10 mAcm−2, exhibiting that the transition metal based MOF has good efficiency as compared to the rare earth metal MOF. The grown catalysts enable additional reaction sites and open up new channels, besides it approaches quick electron transfer in V2O5@C through a carbon bridge. Thus, the porous skeleton of the resulting hybrid catalyst showed superior electrical conductivity, boosting electrochemical properties and making it an efficient and durable electrocatalyst for industrial-scale water electrolysis.