Oxygen Evolution Reaction In Alkaline Media Research Articles

Highly Efficient Alkaline Water Splitting with Ru-Doped Co-V Layered Double Hydroxide Nanosheets as a Bifunctional Electrocatalyst.

Active electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are decisive for achieving efficient energy conversion from electricity to hydrogen fuel through water electrolysis. In this study, tremella-like Ru-doped Co-V layered double hydroxide nanosheets on Ni Foam (Ru-CoV-LDH@NF) was fabricated by a one-pot solvothermal reaction. As-prepared Ru-CoV-LDH@NF, with a nominal Ru loading of around 51.6 μg cm-2 exhibits excellent bifunctional catalytic activity towards HER and OER in alkaline media. To accomplish a current density of 10 mA cm-2 , it demands 32 mV and 230 mV overpotentials for HER and OER, respectively. The alkali electrolyzer utilizing Ru-CoV-LDH/NF as bifunctional electrocatalyst affords 10 mA cm-2 electrolytic current density at an extremely low cell voltage of 1.50 V, showing excellent performance compared to a Pt/C-RuO2 -based electrolyzer and many other bifunctional electrocatalyst-based ones. The incorporation of Ru changes the morphology of the resultant nanosheets to offer high electrochemical surface areas for electrocatalysis; at the same time, it significantly boosts the intrinsic HER/OER electrocatalytic activity. For HER, the energy barrier of the Volmer step is efficiently reduced upon Ru doping, whereas the Ru dopants optimize the absorption strength of *O intermediates to facilitate the OER process. This work offers a feasible means to optimize the Co-based hydroxide materials for improved electrocatalysis in overall water splitting.

Inception of Co3O4 as Microstructural Support to Promote Alkaline Oxygen Evolution Reaction for Co0.85Se/Co9Se8 Network.

Developing electrocatalysts with abundant active sites is a substantial challenge to reduce the overpotential requirement for the alkaline oxygen evolution reaction (OER). In this work, we have aimed to improve the catalytic activity of cobalt selenides by growing them over the self-supported Co3O4 microrods. Initially, Co3O4 microrods were synthesized through annealing of an as-prepared cobalt oxalate precursor. The subsequent selenization of Co3O4 resulted in the formation of a grainy rodlike Co3O4/Co0.85Se/Co9Se8 network. The structural and morphological analysis reveals the presence of Co3O4 even after the selenization treatment where the cobalt selenide nanograins are randomly covered over the Co3O4 support. The resultant electrode shows superior electrocatalytic activity toward OER in alkaline medium by delivering a benchmark current density of 10 mA/cm2geo at an overpotential of 330 mV. As a comparison, we have developed Co0.85Se/Co9Se8 under similar conditions and evaluated its OER activity. This material consumes an overpotential of 360 mV to deliver the benchmark current density, which signifies the role of the Co3O4 support to improve the electrocatalytic activity of Co0.85Se/Co9Se8. Despite having a low TOF value for Co3O4/Co0.85Se/Co9Se8 (0.0076 s-1) compared to Co0.85Se/Co9Se8 (0.0102 s-1), the improved catalytic activity of Co3O4/Co0.85Se/Co9Se8 is attributed to the presence of a higher number of active sites rather than the improved per site activity. This is further supported from the Cdl (double layer capacitance) measurements where Co3O4/Co0.85Se/Co9Se8 and Co0.85Se/Co9Se8 tender Cdl values of about 8.19 and 1.08 mF/cm2, respectively, after electrochemical precondition. As-prepared Co3O4/Co0.85Se/Co9Se8 also manifests rapid kinetics (low Tafel slope ∼ 91 mV/dec), long-term stability, low charge-transfer resistance, and 82% Faradaic efficiency for alkaline electrocatalysis (pH = 14). Furthermore, the proton reaction order (ρRHE) is found to be 0.65, indicating a proton decoupled electron transfer (PDET) mechanism for alkaline OER. Thus, the Co3O4 support helps in the exposure of more catalytic sites of Co0.85Se/Co9Se8 to deliver the improved catalytic activities in alkaline medium.

Facile Synthesis of Hierarchical CuS and CuCo2S4 Structures from an Ionic Liquid Precursor for Electrocatalysis Applications.

Covellite-phase CuS and carrollite-phase CuCo2S4 nano- and microstructures were synthesized from tetrachloridometallate-based ionic liquid precursors using a novel, facile, and highly controllable hot-injection synthesis strategy. The synthesis parameters including reaction time and temperature were first optimized to produce CuS with a well-controlled and unique morphology, providing the best electrocatalytic activity toward the oxygen evolution reaction (OER). In an extension to this approach, the electrocatalytic activity was further improved by incorporating Co into the CuS synthesis method to yield CuCo2S4 microflowers. Both routes provide high microflower yields of >80 wt %. The CuCo2S4 microflowers exhibit a superior performance for the OER in alkaline medium compared to CuS. This is demonstrated by a lower onset potential (∼1.45 V vs RHE @10 mA/cm2), better durability, and higher turnover frequencies compared to bare CuS flowers or commercial Pt/C and IrO2 electrodes. Likely, this effect is associated with the presence of Co3+ sites on which a better adsorption of reactive species formed during the OER (e.g., OH, O, OOH, etc.) can be achieved, thus reducing the OER charge-transfer resistance, as indicated by X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy measurements.

Non-metallic electronic regulation in CuCo oxy-/thio-spinel as advanced oxygen evolution electrocatalysts

Developing cost-effective and high-performance oxygen evolution reaction (OER) electrocatalysts has become the intense research on pursuing emerging renewable energy conversion, in which exploring and investigating the intrinsic nature of efficient and stable CuCo spinel catalysts toward OER in alkaline media is highly desirable. Herein, Cu1– x Co2+ x O4 oxy-spinel nanoflakes are fabricated by a facile hydrothermal method with the oxidation of ammonia water. In the same condition, Cu1– x -Co2+ x S4 thio-spinel nanospheres are formed without oxidation. In OER process, the as-obtained Cu1– x Co2+ x O4 nanoflakes and Cu1– x Co2+ x S4 nanospheres possess the anodic overpotential of 267 and 297 mV in alkaline media to drive the current density of 10 mA/cm2, respectively, outperforming the state-of-the-art noble metal catalyst of RuO2. X-ray photoelectron spectroscopy analysis exhibits the higher ratio value of Co(III)/Co(II) in Cu1– x Co2+ x O4 than that in Cu1– x Co2+ x S4, suggesting that the strongly-electronegative oxygen efficiently predominates in regulating valence states of Co active sites in spinel structures. Remarkably, density functional theory simulation further reveals that the increased valence state of Co could accelerate the electron exchange between catalysts and oxygen adsorbates during electrocatalysis, thus contributing to the higher OER activity of Cu1– x Co2+ x O4 catalysts. This work provides deep insight regarding the significance of non-metal element (O and S) in CuCo spinel structure catalysts, as well as presents a promising approach to exploit higher performance and grasp the mechanism of various non-noble-metal spinel catalysts for water oxidation.

Rational hetero-interface design of Fe3N@Ni2Co-LDHs as high efficient electrocatalyst for oxygen evolution reaction

The design of low-cost and efficient electrocatalysts is critical for oxygen evolution reaction (OER) to overcome the high overpotential and sluggish kinetics. Herein, a new non-precious metal electrocatalyst by synergistically coupling spindle-like Fe3N hollow nanorods with Ni2Co layered double hydroxides (Fe3N@Ni2Co-LDHs) was fabricated via annealing spindle-like Fe2O3 hollow nanorods in NH3 atmosphere, followed by refluxing in oil bath in the existence of Co(NO3)2·6H2O, Ni(NO3)2·6H2O, urea and polyvinylpyrrolidone (PVP). Impressively, the Fe3N@Ni2Co-LDHs nanohybrids with heterointerfaces shows remarkable OER performance with extremely low overpotential (only 240 mV to achieve a current density of 10 mA cm−2) and small Tafel slope (38.9 mV dec−1) for OER in alkaline medium. The enhanced OER performance could be attributed to the strong interfacial interaction between Fe3N and Ni2Co-LDHs, and improved electrical conductivity of the nanohybrids. This work might provide a feasible route for the development of efficient electrocatalysts with hetero-interfaces in renewable energy system.

Crystalline NiFe layered double hydroxide with large pore volume as oxygen evolution electrocatalysts

Cost-effective and earth-abundant electrocatalysts with high activity for oxygen evolution reaction (OER) is essential for achieving efficient and economical electrochemical water splitting. In this work, we developed a facile low-temperature coprecipitation approach to synthesize NiFe layered double hydroxide (NiFe LDH). By tuning Ni/Fe feed ratio and using Na2CO3 as precipitant, mesoporous NiFe LDH nanoparticles were obtained. The special physicochemical features of these NiFe LDH nanoparticles, including high degree of crystallization, large pore volume and abundant crystalline/amorphous interfaces, synergistically endowed the catalyst with enriched active sites. Consequently, the optimal Ni0.66Fe0.33 LDH electrocatalyst showed excellent activity toward OER in alkaline media, with a low overpotential of 248 mV to deliver a current density of 10 mA cm−2, a small Tafel slope of 46 mV dec−1, and strong durability. This work opens an innovative avenue toward the design of advanced NiFe-based catalysts.

Multifunctional Active‐Center‐Transferable Platinum/Lithium Cobalt Oxide Heterostructured Electrocatalysts towards Superior Water Splitting

AbstractDesigning cost‐effective and efficient electrocatalysts plays a pivotal role in advancing the development of electrochemical water splitting for hydrogen generation. Herein, multifunctional active‐center‐transferable heterostructured electrocatalysts, platinum/lithium cobalt oxide (Pt/LiCoO2) composites with Pt nanoparticles (Pt NPs) anchored on LiCoO2 nanosheets, are designed towards highly efficient water splitting. In this electrocatalyst system, the active center can be alternatively switched between Pt species and LiCoO2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Specifically, Pt species are the active centers and LiCoO2 acts as the co‐catalyst for HER, whereas the active center transfers to LiCoO2 and Pt turns into the co‐catalyst for OER. The unique architecture of Pt/LiCoO2 heterostructure provides abundant interfaces with favorable electronic structure and coordination environment towards optimal adsorption behavior of reaction intermediates. The 30 % Pt/LiCoO2 heterostructured electrocatalyst delivers low overpotentials of 61 and 285 mV to achieve 10 mA cm−2 for HER and OER in alkaline medium, respectively.

Multifunctional Active-Center-Transferable Platinum/Lithium Cobalt Oxide Heterostructured Electrocatalysts towards Superior Water Splitting.

Designing cost-effective and efficient electrocatalysts plays a pivotal role in advancing the development of electrochemical water splitting for hydrogen generation. Herein, multifunctional active-center-transferable heterostructured electrocatalysts, platinum/lithium cobalt oxide (Pt/LiCoO2 ) composites with Pt nanoparticles (Pt NPs) anchored on LiCoO2 nanosheets, are designed towards highly efficient water splitting. In this electrocatalyst system, the active center can be alternatively switched between Pt species and LiCoO2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Specifically, Pt species are the active centers and LiCoO2 acts as the co-catalyst for HER, whereas the active center transfers to LiCoO2 and Pt turns into the co-catalyst for OER. The unique architecture of Pt/LiCoO2 heterostructure provides abundant interfaces with favorable electronic structure and coordination environment towards optimal adsorption behavior of reaction intermediates. The 30 % Pt/LiCoO2 heterostructured electrocatalyst delivers low overpotentials of 61 and 285 mV to achieve 10 mA cm-2 for HER and OER in alkaline medium, respectively.

SnO2 QDs@CoFe2O4 NPs as an efficient electrocatalyst for methanol oxidation and oxygen evolution reactions in alkaline media

We successfully decorated SnO2 quantum dots (SQDs) on the surface of spinel cobalt ferrite (CFO) at room temperature by cost-effective method. Pristine CFO and CFO nanocomposites (CFO-Sn1 and CFO-Sn2) were used as an electrocatalyst for methanol oxidation reaction (MOR) and oxygen evolution reaction (OER). CFO-Sn2 led to superior MOR and OER in alkaline media owing to the improved conductivity and higher electrochemically active surface area compared to the pristine CFO and CFO-Sn1. CFO-Sn2 exhibited the highest anodic peak intensity (Ipc) for MOR and significant peak separation upto 4.0 M concentration of MeOH. CFO-Sn2 exhibited the lowest overpotential value of 290 mV at 10 mA cm−2 vs RHE for OER, which was the highest among the electrocatalyst, and a Tafel slope of 85 mV/dec.

Boosting oxygen evolution reaction performance by nickel substituted cobalt-iron oxide nanoparticles embedded over reduced graphene oxide

Designing non-precious-metal (NPM) electrocatalysts for oxygen evolution reaction (OER) from alkaline water is of paramount importance for clean, sustainable and conversion technologies. Herein, we report a facile, scalable and rapid microwave assisted synthesis to produce Ni substituted cobalt-iron oxides Co1-xNixFe2O4 (x = 0, 0.10, 0.25, 0.50, 0.75 and 1) supported over conductive reduced graphene oxide (rGO) and successfully employing them as electrode materials for OER in alkaline medium. Interestingly, by tuning Ni amount in cobalt-iron oxide has a profound influence on the OER activity i.e., Co0.75Ni0.25Fe2O4/rGO exhibits the best OER performance with an overpotential of 440 mV at 10 mA cm−2 and considerable electrochemical stability over 1000 cycles and even up to 10 h in 0.1 M KOH solution.

Nanostructured Carbon-Nitrogen-Sulfur-Nickel Networks Derived From Polyaniline as Bifunctional Catalysts for Water Splitting.

The development of reliable production routes for sustainable hydrogen (H2), which is an essential feedstock for industrial processes and energy carrier for fuel cells, is needed. It appears to be an unavoidable alternative to significantly reduce the dependence on conventional energy sources based on fossil fuels without increasing the atmospheric CO2 levels. Among the different power-to-X scenarios to access high purity H2, the electrochemical approach based on electrolysis looks to be a promising sustainable solution at both the small and large industrial scales. However, the practical realization of this important opportunity faces several challenges, including the efficient design of cost-effective catalytic materials to be used as a cathode with improved intrinsic and durable activity. In this contribution, we report the design and development of efficient nanostructured catalysts for the electrocatalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in aqueous media, whereby noble metal-free elements are embedded in a matrix of a conducting polymer, polyaniline (PANI). To increase the electrical conductivity and further the electrocatalytic ability toward HER of the chemically polymerized PANI in the presence of nickel (II) salt (nitrate), the PANI-based materials have first been stabilized at a mild temperature of 250–350°C in air and then carbonized at 800–1,000°C under nitrogen gas to convert the chemical species into nitrogen, sulfur, nickel, and carbon nanostructured networks (CNNs). Different physicochemical (TGA-DSC, Raman spectroscopy, XRD, SEM, EDX, ICP, CHNS, BET, and XPS) and electrochemical (voltammetry and electrochemical impedance spectrometry) methods have been integrated to characterize the as-synthesized CNNs materials and interrogate the relationship of material-to-performance. It has been found that those synthesis conditions allow for the substantial increase of the electrocatalytic performance toward HER and OER in alkaline media in terms of the onset potential and charge transfer resistance and overpotential at the specific activity of 10 milliamps per square centimeter, thus ranking the present materials among the most efficient noble metal-free catalysts and making them possible candidates for integration in practical low-energy consumption alkaline electrolyzers.

Multiscale structural optimization: Highly efficient hollow iron-doped metal sulfide heterostructures as bifunctional electrocatalysts for water splitting

Hollow iron-doped Co–Mo sulfide (H–Fe–CoMoS) heterostructures with a highly efficient water-splitting catalytic ability were achieved by applying a multiscale optimization strategy. Morphological and compositional optimization on a macroscale achieved by assembling a bimetallic Co–Mo sulfide (CoMoS) heterostructure in a hollow-structured composite (H–CoMoS) gave the electrocatalyst an ability to conduct enhanced bifunctional activities for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Intrinsic electronic structure optimization on a microscale achieved by introducing a small amount of iron (Fe) into H–CoMoS (H–Fe–CoMoS) further improved its catalytic activity and stability. Electrochemical measurements revealed that this multiscale structural optimization promoted enhanced electrical conductivity and increased the number of electrochemical active sites on the H–Fe–CoMoS, leading to its remarkable electrocatalytic performance as a bifunctional catalyst for both HER and OER in alkaline media. The H–Fe–CoMoS showed overpotentials of 282 mV and 137 mV to achieve a current density of 10 mA cm −2 for OER and HER, respectively, which are comparable to the performance of the benchmark OER catalyst RuO 2 and HER catalyst Pt/C. • A multiscale optimization strategy is used to get a highly efficient electrocatalyst. • Bimetallic CoMoS heterostructures show bifunctional activities for both HER and OER. • Nanosized hollow metal sulfide was prepared using block polymer as a soft-template. • Fe-doping into the catalyst facilitates water splitting kinetics.

Efficient catalysis of N doped NiS/NiS2 heterogeneous structure

Boosting the catalytic ability of nickel sulfide is vital to its further application as a class of promising non-noble catalysts for energy/environmental applications. In light of the varied structure phase and heteroatom doping effect of nickel sulfide, herein, we demonstrated the excellent catalysis performance for varied reactions catalyzed by nickel sulfide with N doping and heterostructure construction. Different from the usually used corrosive precursors, amidinothiourea and thioacetamide were used as S and N source for the catalysts fabrication, and N atom was doped into the catalysts simultaneously during the sulfuration process. The spectroscopic probing and microscopic observation clearly showed the heterogeneous structure and interface formation. Benefiting from the large surface area, N-doping induced electronic effect and interfacial coupling and synergistic effect between NiS and NiS2, the as-prepared N doped NiS/NiS2 (N-NiS/NiS2) heterogeneous catalyst can realize multifunctional catalysis for hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and urea oxidation reaction (UOR) efficiently in terms of the high activity, favorable kinetics, rapid charge transfer and strong durability. Specifically, N-NiS/NiS2 catalyst exhibited low overpotentials of 185 and 270 mV to deliver a current density of 10 mA cm−2 for HER and OER in alkaline media, respectively. Meanwhile, the N-NiS/NiS2 catalyst could reach 100 mA cm−2 at 1.47 V for UOR, about 130 mV less for its OER. When integrated into a two-electrode system for water electrolysis, the electrode delivered a potential of 1.62 V to achieve 10 mA cm−2 for urea electrolysis which was 120 mV lower than that of conventional water electrolysis. The work shows the importance of the heterostructure interface construction and hetero-atom doping effect on catalysis ability promotion.

FeCoNi Sulfides Derived From In situ Sulfurization of Precursor Oxides as Oxygen Evolution Reaction Catalyst.

It is highly promising to design and develop efficient and economical electrocatalysts for oxygen evolution reaction (OER) in alkaline solution. In this work, we prepare FeCoNi sulfide composites (including FeS, Co3S4, and Ni3S4) derived from in situ sulfurization of precursor oxides on carbon cloth (CC), which are used to become an OER catalyst. Such catalyst shows excellent OER performance, low overpotential, small Tafel slope, and high electrochemical stability, and it is a promising electrocatalyst for OER in alkaline media.

Synergistic effect of metallic nickel and cobalt oxides with nitrogen-doped carbon nanospheres for highly efficient oxygen evolution

The most energy-inefficient step in the oxygen evolution reaction (OER), which involves a complicated four-electron transfer process, limits the efficiency of the electrochemical water splitting. Here, well-defined Ni/Co3O4 nanoparticles coupled with N-doped carbon hybrids (Ni/Co3O4@NC) were synthesized via a facile impregnation-calcination method as efficient electrocatalysts for OER in alkaline media. Notably, the impregnation of the polymer with Ni and Co ions in the first step ensured the homogeneous distribution of metals, thus guaranteeing the subsequent in situ calcination reaction, which produced well-dispersed Ni and Co3O4 nanoparticles. Moreover, the N-doped carbon matrix formed at high temperatures could effectively prevent the aggregation and coalescence, and regulate the electronic configuration of active species. Benefiting from the synergistic effect between the Ni, Co3O4, and NC species, the obtained Ni/Co3O4@NC hybrids exhibited enhanced OER activities and remarkable stability in an alkaline solution with a smaller overpotential of 350 mV to afford 10 mA cm−2, lower Tafel slope of 52.27 mV dec−1, smaller charge-transfer resistance, and higher double-layer capacitance of 25.53 mF cm−2 compared to those of unary Co3O4@NC or Ni@NC metal hybrids. Therefore, this paper presents a facile strategy for designing other heteroatom-doped oxides coupled with ideal carbon materials as electrocatalysts for the OER.

In-situ growth of novel CNTs-graphene hybrid structure on Ni-silica nanocomposites by CVD method for oxygen evolution reaction

Carbon nanostructures are ideal materials for electrochemical reactions like oxygen evolution reaction (OER) due to excellent electrical conductivity, resistance to strong acidic as well as basic conditions and conductive support material for transition metals. In this work we have synthesized multiwalled carbon nanotubes MWCNTs along with graphene growth in-situ by CVD method at 650 °C on nickel-silica nanocomposites for OER in alkaline medium. After removal of silica, our material exhibited comparable OER performance with that of commercial Iridium supported carbon i.e. Ir/C (20 wt % Ir) electrocatalyst. The OER performance is attributed to the defective nature of MWCNTs in the form of surface discontinuities found on rolled graphene layers of carbon nanotubes along with MWCNTs-graphene interfaces which presumably contain dangling bonds as active sites for OER. The overpotential at current density of 10 mA/cm2 exhibited by MWCNTs-graphene hybrid carbon nanostructured material was 310 mV in 1 M KOH solution at scan rate of 5 mV/s while commercial Ir/C material revealed overpotential of 305 mV under similar conditions.

Surface Engineering on Nickel-Ruthenium Nanoalloys Attached Defective Carbon Sites as Superior Bifunctional Electrocatalysts for Overall Water Splitting.

Herein, we report a novel catalyst of nickel-ruthenium alloy nanoparticles (NPs) homogeneously enriched in the wall of multiwalled carbon nanotubes (denoted as NiRu@MWCNTs) via a facile plasma reduction method. The NiRu@MWCNTs exhibits remarkable electrocatalytic activity and stability for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The required overpotentials to drive a current density of 10 mA cm-2 (η10) over NiRu@MWCNTs are only 14 and 240 mV, corresponding to Tafel slopes of 32 and 55 mV dec-1 for the HER and OER in alkaline medium, respectively. Furthermore, the NiRu@MWCNTs electrolyzer shows low η10 of 330, 380, and 280 mV in acidic, neutral, and alkaline media, respectively. Density functional theory (DFT) calculations and experimental results reveal that the NiRu alloy NPs attached to the defective and nondefective carbon are the key active sites for the HER and OER, respectively, thus resulting in superior isolated synergistic bifunctional active sites for overall water splitting. Our work provides a promising strategy for efficient synthesis of robust catalysts with specific bifunctional active sites for overall water splitting in a wide pH range, along with deep insight into the catalytic mechanism.

Impact of the NiO nanostructure morphology on the oxygen evolution reaction catalysis

The oxygen evolution reaction (OER) is still a barrier to energy generation technologies, motivating the development of new strategies to the rational use of electrodes for OER. This work reports the effect of the morphology of nickel oxide (NiO) nanostructures on their catalytic activity toward OER in alkaline medium. 1D hollow nanofibers (NiO-NFBs) synthesized by solution blow spinning are compared with 3D nanoparticles (NiO-NPTs) synthesized by a well-known citrate method. The intrinsic activity of the electrocatalysts was evaluated by linear sweep voltammetry (LSV), electrochemically active surface area (ECSA), turnover frequency (TOF), and electrochemical impedance spectroscopy (EIS). Results confirm the superiority of NiO-NFBs, with a remarkable difference of 133 mV versus RHE to generate j = 10 mA cm−2. The NiO-NFBs showed a TOF value 122 times higher than NiO-NPTs. The Tafel analysis and EIS revealed that the hollow structure favors kinetics through a more efficient process of mass and charge transfer. Overall, results corroborate the thesis that the morphology imposes the main rule on the electrocatalyst performance. The morphology of NiO-NFBs is fully preserved after the electrolysis test, while NiO-NPTs degrade through a nanoparticle coalescence mechanism. This work is a contribution to the state of the art of nanostructured NiO-based electrodes for OER.

Ternary FeCoNi alloy nanoparticles embedded in N-doped carbon nanotubes for efficient oxygen evolution reaction electrocatalysis

The development of highly active and low-cost electrocatalysts toward oxygen evolution reaction (OER), especially the non-noble metal electrocatalysts with well-defined nanostructures, is of great significance for the practical application in metal–air batteries and overall water splitting. Herein, we report a simple pyrolysis method to construct the ternary FeCoNi alloy nanoparticles that encapsulated with bamboo-like N-doped carbon nanotubes (N-CNTs). By combining the advantages of FeCoNi alloy with N-CNTs, the as-fabricated FeCoNi@N-CNTs have large active surface area, ultrahigh content of graphitic carbon, and abundant active metal–C/Nx species to show better electrocatalytic performance for OER in alkaline media. The optimized Fe1Co1Ni1@N-CNTs displays perfect electrocatalytic performance toward OER with an unexpectedly small onset potential of 1.43 V and an ultralow overpotential of 249 mV at 10 mA cm−2, as well as remarkable long-time stability in alkaline media. More importantly, by coupling Fe1Co1Ni1@N-CNTs as the anode electrode, our previous reported Fe1Co3Mo3 P–O as cathode electrode, a potential of only 1.62 V is needed to drive the water electrolysis to reach to the current density of 10 mA cm−2, comparable to the state-of-the-art IrO2 ‖ Pt/C couple. This work provides new perspectives for constructing efficient and stable N-CNTs encapsulated non-precious metal electrocatalysts for OER.

An Efficient Electrocatalyst for Oxygen Evolution Reaction in Alkaline Solutions Derived from a Copper Chelate Polymer via In Situ Electrochemical Transformation

Efficient oxygen evolution reaction (OER) electrocatalysts are highly desired in the field of water electrolysis and rechargeable metal-air batteries. In this study, a chelate polymer, composed of copper (II) and dithiooxamide, was used to derive an efficient catalytic system for OER. Upon potential sweep in 1 M KOH, copper (II) centers of the chelate polymer were transformed to CuO and Cu(OH)2. The carbon-dispersed CuO nanostructures formed a nanocomposite which exhibits an enhanced catalytic activity for OER in alkaline media. The nanocomposite catalyst has an overpotential of 280 mV (at 1 mA/cm2) and a Tafel slope of 81 mV/dec in 1M KOH solution. It has a seven-fold higher current than an IrO2/C electrode, per metal loading. A catalytic cycle is proposed, in which CuO undergoes electrooxidation to Cu2O3 that further decomposes to CuO with the release of oxygen. This work reveals a new method to produce an active nanocomposite catalyst for OER in alkaline media using a non-noble metal chelate polymer and a porous carbon. This method can be applied to the synthesis of transition metal oxide nanoparticles used in the preparation of composite electrodes for water electrolyzers and can be used to derive cathode materials for aqueous-type metal-air batteries.