Oxygen Evolution Reaction In Alkaline Media Research Articles

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.

Effect of carbon support on the activity of monodisperse Co45Pt55 nanoparticles for oxygen evolution in alkaline media.

Oxygen evolution reaction (OER) represents the efficiency-limiting reaction in water electrolyzers, metal-air batteries, and unitized regenerative fuel cells. To achieve high-efficiency OER in alkaline media, we fabricated three novel electrocatalysts by the assembly of as-prepared Co45Pt55 alloy nanoparticles (NPs) on three different carbon-based support materials: reduced graphene oxide (CoPt/rGO), mesoporous graphitic carbon nitride (CoPt/mpg-CN), and commercial Ketjenblack carbon (CoPt/KB). Voltammetry studies revealed that CoPt/rGO electrocatalyst provided lower OER overpotentials accompanied by higher currents and specific current density values than the other two studied materials. Moreover, CoPt/rGO outperformed commercial CoPt/C electrocatalysts in terms of notably higher specific current densities. Additionally, it was found that CoPt/rGO electrocatalyst activity increases with increasing temperature up to 85°C, as suggested by the increase in the exchange current density. Electrochemical impedance spectroscopy studies of three electrocatalysts in OER revealed similar charge transfer resistance, although CoPt/rGO provided a higher current density. The main issue observed during long-term chronoamperometry and chronopotentiometry studies is the materials' instability under OER polarization conditions, which is still to be tackled in future work.

NiCoP-nanocubes-decorated CoSe2 nanowire arrays as high-performance electrocatalysts toward oxygen evolution reaction

Designing effective, robust, and low-cost catalysts for oxygen evolution reaction (OER) is an urgent requirement yet challenging task in water electrolysis. In this study, a NiCoP-nanocubes-decorated CoSe2 nanowires arrays three-dimensional/two-dimensional (3D/2D) electrocatalyst (NiCoP-CoSe2-2) was developed for catalyzing OER via a combined selenylation, co-precipitation, and phosphorization method. The as-obtained NiCoP-CoSe2-2 3D/2D electrocatalyst exhibits a low overpotential of 202 mV at 10 mA cm−2 with a small Tafel slope of 55.6 mV dec−1, which is superior to most of reported CoSe2 and NiCoP-based heterogeneous electrocatalysts. Experimental analyses and density functional theory (DFT) calculations proof that the interfacial coupling and synergy between CoSe2 nanowires and NiCoP nanocubes are not only beneficial to strengthen the charge transfer ability and accelerate reaction kinetics, but also facilitate the optimization of interfacial electronic structure, thereby enhancing the OER property of NiCoP-CoSe2-2. This study offers insights for the investigation and construction of transition metal phosphide/selenide heterogeneous electrocatalyst toward OER in alkaline media and broadens the prospect of industrial applications in energy storage and conversion fields.

Plasma-Induced Oxygen Vacancies in N-Doped Hollow NiCoPBA Nanocages Derived from Prussian Blue Analogue for Efficient OER in Alkaline Media.

Although water splitting is a promising method to produce clean hydrogen energy, it requires efficient and low-cost catalysts for the oxygen evolution reaction (OER). This study focused on plasma treatment's significance of surface oxygen vacancies in improving OER electrocatalytic activity. For this, we directly grew hollow NiCoPBA nanocages using a Prussian blue analogue (PBA) on nickel foam (NF). The material was treated with N plasma, followed by a thermal reduction process for inducing oxygen vacancies and N doping on the structure of NiCoPBA. These oxygen defects were found to play an essential role as a catalyst center for the OER in enhancing the charge transfer efficiency of NiCoPBA. The N-doped hollow NiCoPBA/NF showed excellent OER performance in an alkaline medium, with a low overpotential of 289 mV at 10 mA cm-2 and a high stability for 24 h. The catalyst also outperformed a commercial RuO2 (350 mV). We believe that using plasma-induced oxygen vacancies with simultaneous N doping will provide a novel insight into the design of low-priced NiCoPBA electrocatalysts.

Nanocomposite of nickel benzene‐1,3,5‐tricarboxylic acid metal organic framework with multiwalled carbon nanotubes: A robust and effective electrocatalyst for oxygen evolution reaction in water splitting

In the current era, the development of robust, eco‐friendly, and highly efficient electrocatalysts for generating hydrogen energy by water electrolysis has become a major challenge. This work explains the electrocatalytic performance of cost‐effective and amiable novel Ni‐BTC‐MWCNTs‐a as an active and effective electrocatalyst for OER in alkaline media. The catalytic activity of the nanocomposite is increased by heat treatment at 400°C temperature for 3 h. Systematic morphological and structural characterization studies of solvothermal synthesized materials were carried out by X‐ray powder diffraction (XRD) analysis, Fourier transform infrared (FTIR) spectroscopy technique, scanning electron microscopy (SEM) analysis, and energy dispersive X‐ray spectroscopy (EDS) analysis techniques. Metal–organic framework (MOF)‐based composites exhibit improved catalytic performance owing to the synergistic effect of Nickel BTC MOF, MWCNTs support, and high‐temperature annealing (400°C). Among all as‐synthesized materials, the annealed Ni‐BTC‐MWCNT‐a exhibits admirable catalytic performance for oxygen evolution reaction (OER) at low value for over potential (η) 243 m V, small Tafel slope value 57 mV dec−1, smaller charge transfer resistance (0.274 Ω), and higher electrochemical active surface area (2000 cm2) with maximum durability for 23 h and utilized as auspicious alternate with excellent catalytic activity in water splitting OER process for producing hydrogen energy at large scale other than highly expensive electrocatalysts of Ir, Ru, Pd, and Pt oxides.

High-entropy (Oxy)hydroxide Prepared by Electrodeposition for Highly Efficient OER in Alkaline Medium

With the development of the economy and society, energy shortage and environmental pollution are increasingly in the spotlight. Electrolytic water to hydrogen technology is considered to be the best way to produce green hydrogen. However, the slow thermodynamic/kinetic limitations make it difficult to scale application due to an anodic oxygen evolution reaction (OER) involving four electrons. Recently, transition metal-based materials become popular research subjects because properties of abundant reserve and low cost. Fortunately, the performances for water splitting are surprising compared to some noble metal-based materials which means these materials have huge potential for practical application in reality. The transition metal (oxy)hydroxides are confirmed to be a category of promising electrocatalysts for OER. To improve the activity of catalysts, many effective strategies (including defects engineering, vacancy engineering, interface engineering, high-entropy effect, etc.) are adopted to modulate the electronic structure and enrich active site density. In this work, we have successfully synthesized high-entropy transition metal (oxy)hydroxides by one-step electrodeposition for water oxidation. The results obtained confirmed the high-entropy effect results in high intrinsic activity and high stability for electrochemical water oxidation.

Effect of Metal Layer Support Structures on the Catalytic Activity of NiFe(oxy)hydroxide (LDH) for the OER in Alkaline Media

AbstractPhotoelectrochemical (PEC) cells promise to combine the benefits of photovoltaics and electrolysis in one device. They consist of a photoabsorber functionalized with an electrocatalyst to harvest faradaic currents under reduced overpotentials. To protect the absorber from the harsh reaction conditions, a protective buffer layer (e. g. TiO2) is added between absorber and catalyst. In this work, we investigate the influence of the catalyst support systems Ti/TiOx and Ti/TiOx/M (M=Au, Ni, Fe) on the overall activity and stability of nickel and iron mixed layered double hydroxides for the alkaline oxygen evolution reaction (OER). The catalyst performance on the bare Ti/TiOx substrate is very poor, but the incorporation of a metallic interlayer leads to two orders of magnitude higher OER current densities. While a similar effect has been observed for M=gold supported systems, we show that the same effect can be achieved with M=nickel/iron, already contained in the catalyst. This proprietary metal interlayer promises a cheap OER performance increase for PEC cells protected with titania buffer layers. Detailed XPS show an improved transformation of the starting catalyst material into the highly active (oxy)hydroxide phase, when using metallic interlayers. From these experiments a pure conductivity enhancement was excluded as possible explanation, but instead an additional change in the local atomic and electronic structure at the metal‐support and metal‐catalyst interfaces is proposed.

In situ facile fabrication of ultrathin Co(OH)2-CoO/graphene oxide nanosheet hybrids with superior oxygen evolution reaction performance

As representative electrocatalysts for the oxygen evolution reaction (OER), Co-based hydroxides and oxides generally suffer from poor electron conductivity and severe self-agglomeration, substantially hindering their wide application in catalysis. To overcome such issues, we herein report a convenient electrostatic adsorption-assisted solvothermal method for the in situ fabrication of ultrathin Co(OH)2-CoO/graphene oxide nanosheet hybrids (denoted as Co-O-H NSs/GO-x) as efficient electrocatalysts for the OER in alkaline media. Notably, the optimal Co-O-H NSs/GO-1.4 mg sample with a thickness of 3.5–3.8 nm demonstrated outstanding electrocatalytic OER performance, with a low overpotential of only 283 mV at 10 mA cm−2 and a small Tafel slope of 57 mV dec−1, making it comparable to state-of-the-art Co-based non-self-supporting electrocatalysts. Comprehensive analysis revealed that the superior OER electrocatalytic performance of Co-O-H NSs/GO-1.4 mg could be ascribed to the synergistic contribution from the enlarged electroactive surface area (approximately 146 mF.cm−2 for its double-layer capacitance), higher electron concentration (approximately 8.1 × 1017 cm−3), enriched oxygen vacancies (accounting for approximately 74.3 % of the oxygen content) and the upshift of the 3d-band centre caused by the high-quality coupling between Co-O-H NSs and GO NSs. This work provides a universal synthetic strategy for the facile construction of high-performance hybrid nanosheet-based catalysts, showing particular importance for establishing efficient energy conversion reactions.

Efficient Oxygen Evolution Reaction Catalyzed by Ni/NiO Nanoparticles Produced by Pulsed Laser Ablation in Liquid Environment

Electrochemical water‐splitting, sustained by renewable energy, is aimed at green H2 production. Efficient and sustainable electrocatalysts are required for a proper energy transition. Oxygen evolution reaction (OER) in alkaline electrolyte can be pursued by using earth‐abundant elements‐based catalysts, such as Ni oxyhydroxides. A proper optimization of intrinsic properties and synthesis procedure is still needed. Herein, the synthesis of Ni/NiO nanoparticles (NPs) through a physical and green technique, pulsed laser ablation in liquid (PLAL), is presented. Ablating a Ni target in deionized water, at different ablation times, leads to NP dispersions used for realization of OER electrode onto graphene paper. Ion‐beam analysis of catalysts amount and homogeneity of NP‐based electrode is performed for the electrode optimization in terms of electrochemical performances. An overpotential at 10 mA cm−2 of 306 mV is achieved for 40 μg cm−2 of catalyst, while lowering the catalyst amount to 8 μg cm−2, unprecedented turnover frequency of 0.20 s−1 and mass activity of ≈1.3 A mg−1 are reached. These data show that Ni/NiO NPs produced by PLAL are highly effective for OER in alkaline media and encourage the use of PLAL as a green and efficient technique for electrocatalyst production.

Surfactant Improved Interface Morphology and Mass Transfer for Electrochemical Oxygen-Evolving Reaction

The surface microstructure of a catalyst coating layer directly affects the active area, hydrophilicity and hydrophobicity, and the high porosity is desirable especially for solid–liquid–gas three-phase catalytic reactions. However, it remains challenging to customize catalyst distribution during the coating process. Here, we report a simple strategy for achieving ultrafine nanocatalyst deposition in a porous structure via introducing the surfactant into coating inks. For a proof-of-concept demonstration, we spin-coated the nanoscale IrO2 sol with a surfactant of sodium dodecyl sulfate (SDS) onto the glassy carbon (GC) electrode for oxygen evolution reaction (OER). Due to the surfactant action, the deposited IrO2 nanocatalyst is evenly distributed and interconnected into a highly porous overlayer, which facilitates electrolyte permeation, gas bubble elimination and active-site accessibility, thus affording high-performance OER in alkaline media. Particularly, the SDS-modified electrodes enable the industrial-level high-current-density performance via enhanced mass transfer kinetics. Such manipulation is effective to improve the coating electrodes’ catalytic activity and stability, and scalable for practical applications and suggestive for other gas-evolving electrodes.

An efficient and durable bifunctional electrocatalyst based on PdO and Co2FeO4 for HER and OER

The adoption of effective, minimal, and versatile electrocatalysts for water splitting to generate hydrogen fuels is of critical importance. The bulk of newly described materials have considerable onset potential, but their electrocatalytic activity is limited by weak electrical conductivity and a limited range of catalytic sites. The combination of a few precious metals added with transition metal-based compounds is a novel and captivating approach. Herein, cobalt ferrite oxide (Co2FeO4) @ palladium oxide (PdO) nanostructures have been prepared through the combined use of hydrothermal and ultraviolet (UV) irradiation techniques. For hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) kinetics, the modified composition offers a high concentration of active sites, improved electrical conductivity, and stability. The Co, Fe, and Pd ions at the composite system's interface may affect the adsorption energy of reaction intermediates synergistically, enabling the process to continue with less potential. The electrocatalyst Co2FeO4@PdO demonstrates an excellent bifunctional approach to electrochemical water splitting (EWS) for HER and OER in alkaline medium. As-prepared electrocatalyst shows an overpotential value of 269 and 259 mV for HER and OER at 10 and 20 mA/cm2 current densities respectively. The low charge transfer resistance values such as 72.2 and 62.4 Ω and durability for 48 h has been observed toward HER and OER, support this material as an efficient and durable electrocatalyst for energy conversion systems.

Morphology-Dependent Electrocatalytic Behavior of Cobalt Chromite toward the Oxygen Evolution Reaction in Acidic and Alkaline Medium.

Exploiting an affordable, durable, and high-performance electrocatalyst for the oxygen evolution reaction (OER) under lower pH condition (acidic) is highly challengeable and much attractive toward the hydrogen-based energy technologies. A spinel CoCr2O4 is observed as a potential noble-metal-free candidate for OER in alkaline medium. The presence of Cr further leads to electronic structure modulation of Co3O4 and thereby greatly increases the corrosive resistance toward OER in acidic environment. Herein, a typical CoCr2O4 with three different morphologies was synthesized for the very first time and employed as an electrocatalyst for OER in alkaline (1 M KOH) and acidic (0.5 M H2SO4) medium. Moreover, different morphologies display a different intrinsic exposed active site and thereby display different electrocatalytic activities. Likewise, the CoCr2O4 Mic (synthesized by the microwave heating method) displays a higher catalytic activity toward OER and delivers a low overpotential of 293 and 290 mV to attain 10 mA/cm2 current density and smaller Tafel slope values of 40 and 151 mV/dec, respectively, in alkaline and acidic environment than the synthesized CoCr2O4 Wet (wet-chemically synthesized) and CoCr2O4 Hyd (hydrothermally synthesized). Moreover, CoCr2O4 Mic exhibits a long-term durability of 24 h (1 M KOH) and 10.5 h (0.5 M H2SO4). The optimized Co-O bond energy in OER condition makes the CoCr2O4 Mic superior than the CoCr2O4 Hyd and CoCr2O4 Wet. Moreover, the substitution of Cr induces the electron delocalization around the Co active species and thereby, positive shifting of the redox potential leads to providing an optimal binding energy for OER intermediates. Also, interestingly, this work represents a catalytic activity trend by a simple experimental result without any complex theoretical calculation. The morphology-dependent electrocatalytic activity obtained in this work will provide a new strategy in the field of electrochemical conversion and energy storage application.