Electrocatalysts For Oxygen Evolution Reaction Research Articles

Biowaste-Derived Enhanced Conductive Carbon Composites as an Ultralow-Cost Electrocatalyst for Oxygen Evolution Reaction

Biowaste-Derived Enhanced Conductive Carbon Composites as an Ultralow-Cost Electrocatalyst for Oxygen Evolution Reaction

Unraveling the Role of the Stoichiometry of Atomic Layer Deposited Nickel Cobalt Oxides on the Oxygen Evolution Reaction.

Nickel cobalt oxides (NCOs) are promising, non-precious oxygen evolution reaction (OER) electrocatalysts. However, the stoichiometry-dependent electrochemical behavior makes it crucial to understand the structure-OER relationship. In this work, NCO thin film model systems are prepared using atomic layer deposition. In-depth film characterization shows the phase transition from Ni-rich rock-salt films to Co-rich spinel films. Electrochemical analysis in 1m KOH reveals a synergistic effect between Co and Ni with optimal performance for the 30 at.% Co film after 500 CV cycles. Electrochemical activation correlates with film composition, specifically increasing activation is observed for more Ni-rich films as its bulk transitions to the active (oxy)hydroxide phase. In parallel to this transition, the electrochemical surface area (ECSA) increases up to a factor 8. Using an original approach, the changes in ECSA are decoupled from intrinsic OER activity, leading to the conclusion that 70 at.% Co spinel phase NCO films are intrinsically the most active. The studies point to a chemical composition dependent OER mechanism: Co-rich spinel films show instantly high activities, while the more sustainable Ni-rich rock-salt films require extended activation to increase the ECSA and OER performance. The results highlight the added value of working with model systems to disclose structure-performance mechanisms.

Nano FeNi-OH/Co(OH)2/NF p-n heterojunction for efficient oxygen evolution reaction and electrocatalytic urea oxidation: Built-In electric field regulated charge distribution and mechanism exploration

Constructing electronic structures with abundant surface/interface structures and effective regulation of catalytic active centers is an effective strategy to improve electrocatalytic performance, but designing efficient bifunctional non-noble metal oxygen evolution reaction (OER) and urea oxidation reaction (UOR) electrocatalysts remains challenging. Studies have shown that p-n heterojunctions can effectively regulate the electronic structure of catalytic active sites while having abundant surface/interface structure, which plays an important role in improving the native catalytic activity. Herein, FeNi-OH/Co(OH)2/NF p-n heterojunction structure was constructed by a simple electrochemical deposition method, and the effects of content, deposition time, and number of cycles on catalytic performance were investigated. The results show that Fe(0.02 M)Ni(0.07 M)–OH(100 s)/Co(OH)2(5)/NF composite material has the best OER and UOR catalytic performance. For OER, the electrocatalyst only requires an overpotential of 271 mV to obtain a current density of 50 mA cm−2, and an applied voltage of 1.56 V to obtain a total water decomposition of 10 mA cm−2 (FeNi-OH/Co(OH)2/NF||Pt). For UOR, a voltage of only 1.314 V (vs. RHE) is required to achieve a current density of 10 mA cm−2, and an applied voltage of 1.44 V can achieve a current density of 10 mA cm−2. Experimental, in situ measurements and theoretical results indicate that the improvement in catalytic activity is mainly due to the potential difference between FeNi-OH and Co(OH)2, which induces self-driven charge transfer at the interface, promoting the adsorption of reactant molecules, optimizing reaction barriers, accelerating chemical bond cleavage, and thus promoting catalytic reactions.

Hf-Doped CoP Hollow Nanocubes as High-Performance Electrocatalyst for Oxygen Evolution Reaction.

Designing and synthesizing hollow frame structures with unique three-dimensional open structures in electrocatalysis remain a challenge. Etching is an effective method to synthesize metal-organic frameworks (MOFs) with a hollow structure and rich function. Herein, we report the design and synthesis of Hf-doped CoP hollow nanocubes by selective etching and ion exchange. Different from the traditional etching method, we used acid xylenol orange solution to etch typically the (211) crystal face of ZIF-67, obtaining the unique bell-like structure, named XO-ZIF-67. Subsequently, Hf-doped CoP hollow nanocubes were formed by Hf4+ doping and simple phosphating treatment. Electrochemical tests showed that the overpotential of the obtained catalyst is only 291 mV at the current density of 10 mA cm-2 when applied in catalyzing the oxygen evolution reaction (OER). Furthermore, the catalyst shows excellent stability when running in 1 M KOH solution for 25 h.

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

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

Facile Carbothermal Synthesis of Metal Phosphides-Based Multifunctional Electrocatalysts via Polyaniline Doped with Phosphoric Acid

Transition metal phosphides (TMPs) and their composites are promising non-platinum electrocatalysts for hydrogen evolution (HER), oxygen evolution (OER), and oxygen reduction (ORR) reactions. But traditional methods to obtain these electrocatalysts are usually multi-step and include the participation of hazardous phosphorus compounds during phosphidation. Here, the possibility of using a polyaniline doped with phosphoric acid (PANI∙H3PO4)—as a source of C, N and P simultaneously - to obtain composites based on N,P-doped carbon and nano- and/or submicron TMP particles as HER, OER and ORR electrocatalysts is demonstrated. The pyrolysis of PANI∙H3PO4 together with Co, Ni, Mo, or Fe salt allows the formation of such composite electrocatalysts by the carbon thermal reduction route. Regardless of the pH of the electrolyte, the MoP-based electrocatalyst is characterized in HER by the smallest Tafel slope and overpotential of hydrogen evolution and also exhibits high stability during long-term operation. At the same time, other composites are multifunctional electrocatalysts possessing activity not only in HER, but also in OER and ORR. The proposed approach can be a starting point for a simple, universal in choice of d-metal, and environmentally attractive preparation of multifunctional TMP-based electrocatalysts with further improvement of their performance.

Augmented Electrochemical Oxygen Evolution by d-p Orbital Electron Coupling.

While high-entropy alloys, high-entropy oxides, and high-entropy hydroxides, are advanced as a novel frontier in electrocatalytic oxygen evolution, their inherent activity deficiency poses a major challenge. To achieve the unlimited goal to tailor the structure-activity relationship in multicomponent systems, entropy-driven composition engineering presents substantial potential, by fabricating high-entropy anion-regulated transition metal compounds as sophisticated oxygen evolution reaction electrocatalysts. Herein, a versatile 2D high-entropy metal phosphorus trisulfide is developed as a promising and adjustable platform. Leveraging the multiple electron couplings and d-p orbital hybridizations induced by the cocktail effect, the exceptional oxygen evolution catalytic activity is disclosed upon van der Waals material (MnFeCoNiZn)PS3, exhibiting an impressively low overpotential of 240mV at a current density of 10mA cm-2, a minimal Tafel slope of 32mV dec-1, and negligible degradation under varying current densities for over 96 h. Density functional theory calculations further offer insights into the correlation between orbital hybridization and catalytic performance within high-entropy systems, underscoring the contribution of active phosphorus centers on the substrate to performance enhancements. Moreover, by achieving electron redistribution to optimize the electron coordination environment, this work presents an effective strategy for advanced catalysts in energy-related applications.

Methanol steam mediated corrosion engineering towards high-entropy NiFe layered double hydroxide for ultra-stable oxygen evolution

Rational design of viable routes to obtain efficient and stable oxygen evolution reaction (OER) electrocatalysts remains challenging, especially under industrial conditions. Here, we provide a solvent-steam assisted corrosion engineering strategy to directly fabricate high-entropy NiFe-LDH with spatially resolved structural order. Ammonium fluoride in methanol steam enables the formation of nanosheets while Fe3+ effectively enhances their adhesion to the semi-sacrificial nickel-iron foam (NFF), thereby conjuring up a NiFe-LDH@NFF catalyst that exhibits remarkable adaptability to robust electrochemical activation yet with excellent stability. Comprehensive measurements reveal the in-situ formation of high-valance metal oxyhydroxide and the enhancement of adsorption-desorption process. Under the industrial condition (6 mol/L KOH, 60 °C), the NiFe-LDH@NFF exhibits excellent activity of 50 mA/cm2 at 1.55 V and high durability of over 120 h at 200 mA/cm2. We anticipate that the steam assisted strategy could promote the development of efficient non-precious electrocatalysts for hydrogen energy.

Template-Assisted in situ synthesis of superaerophobic bimetallic MOF composites with tunable morphology for boosted oxygen evolution reaction

CoFe bimetallic organic frameworks (CoFe-MOFs) with tunable morphology and electronic structure are synthesized in situ utilizing cobalt hydroxide (Co(OH)2) as a semi-sacrificial template and different anionic iron salts as modifying factors in a non-calcined synthesis method. This work defines the impact of three different anionic metallic iron salts (FeCl3, Fe(NO3)3, and Fe2(SO4)3) on the morphology of MOF materials and their resulting oxygen evolution reaction (OER) catalytic activity. Employing ferric chloride (FeCl3) as the metallic iron source, heterostructured electrocatalysts (BN-CoFe-MOF) with nanoparticles decorated nanoneedle tips are obtained, exhibiting a low overpotential (230 mV at 10 mA cm−2) and a Tafel slope of 105.6 mV dec−1 in 1.0 M KOH. It also demonstrates long time stability for at least 50 h at a current density of 10 mA cm−2. The investigation uncovers that the splendid OER activity and stability of the BN-CoFe-MOF heterojunction can be attributed to its large specific surface area, desirable mesoporous structure, superaerophobic characteristic, and high exposure of active centers. This work not only provides an efficient and cost-effective MOF based OER electrocatalyst but also serves as a valuable reference for future research on morphology control and strategies to enhance the OER activity of MOF catalysts.

Construction of Ferric-Oxide-Doped Nickel-Iron Hydroxide Electrocatalysts by Magnetic-Field-Assisted Chemical Corrosion toward Boosted Oxygen Evolution Reaction.

Transition-metal-based oxygen evolution reaction (OER) catalysts have attracted widespread attention due to their inexpensive prices, unique layered structures, and rich active sites. Currently, designing low-cost, sustainable, and simple synthesis methods is essential for the application of transition-metal-based catalysts. Here, magnetic field (MF)-assisted chemical corrosion, as a novel technology, is adopted to construct superior OER electrocatalysts. The produced Ni(Fe)(OH)2-Fe2O3 electrode exhibits an overpotential of 272 mV at a current density of 100 mA cm-2, presenting a 64 mV reduction compared to the electrode without an MF. The experimental results indicate that an MF can induce the directional growth of Fe2O3 rods and reduce their accumulation. In addition, an external MF is beneficial for the lattice dislocation of the obtained catalysts, which can increase the surface free energy, thus reducing the activation energy and accelerating the electrochemical reaction kinetics. This work effectively combines a magnetic field with chemical corrosion and electrochemical energy, which offers a novel strategy for the large-scale development of environmentally friendly and superior electrocatalysts.

Hollow CuCo-based trimetallic oxides derived from ZIF-67 as enhanced electrocatalysts for OER

Multimetallic oxide configuration and hollow structure construction are effective strategies for the design of efficient electrocatalysts, which can regulate the intrinsic properties of the active sites, enlarge the specific surface areas and expose more active sites. In this work, hollow-structured CuCo-based ternary metal oxides supported nitrogen-carbon networks (HS-CuMCoOx, M = Fe/Zn/Ni) derived from ZIF-67 hollow spheres were fabricated through facile ion exchange and heat treatment. The prepared composites possess hollow configurations with homogeneously dispersed trimetallic active species on the shells. Among all the ternary metallic derivatives, hollow spheres supporting Cu, Fe, and Co oxides (HS-CuFeCoOx) exhibited highest electrocatalytic activity towards oxygen evolution reaction (OER). The improved OER performance ascribed to the inherent electrocatalytic properties of the ternary metal active species and microstructure by hollow structure design and heat treatment, which offered an effective synthetic strategy for the fabrication of trimetallic oxide composites for as OER electrocatalysts.

Mn incorporated RuO2 nanocrystals as an efficient and stable bifunctional electrocatalyst for oxygen evolution reaction and hydrogen evolution reaction in acid and alkaline

The development of efficient and stable bifunctional overall water-splitting is a crucial goal for clean and renewable energy, which is a challenging task. Herein, we report an Mn-incorporated RuO2 (Mn-RuO2) catalyst for highly efficient electrocatalytic oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in acid and alkaline media. Benefiting from a more electrochemical active area with the incorporation of Mn, the Mn-RuO2 required an overpotential of 200 mV to attain a current density of 10 mA/cm2 for OER in acid. DFT result indicates that the doping of Mn into RuO2 can enhance the OER activity. An acidic overall water-splitting electrolyzer with good stability constructed by bifunctional Mn-RuO2 only requires a cell voltage of 1.50 V to afford 10 mA/cm2 and can operate stably for 50 h at 50 mA/cm2, which is better than the state-of-the-art Ru-based catalyst. Additionally, the Mn-RuO2 exhibits excellent HER and OER activity in alkaline media, and it shows superior activity and durability for overall water-splitting, only needing a cell voltage of 1.49 V to attain 10 mA/cm2. The present work provides an efficient approach to designing and constructing efficient Ru-based electrocatalysts for overall water-splitting.

Synergetic FeMoSe@NiCo-LDH hybrid heterostructures as a stable and effective bifunctional catalyst for sustained overall water splitting and seawater splitting

Designing cost-effective and highly active and stable earth-abundant-based bifunctional electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is significant, yet challenging task. In this work, we employed synergetic design of FeMoSe@NiCo-LDH heterostructures electrocatalyst to effectively enhance OER and HER performance in the alkaline media by addressing the lethargic kinetics. Combining FeMoSe and NiCo-LDH components as hybrid heterostructure promotes synergistic effects inherently, and influences adsorption free energy and charge transfer, and improves overall reaction kinetics and durability. The FeMoSe@NiCo-LDH hybrid heterostructure catalyst demonstrates low overpotential of 240 mVRHE for OER and 170 mVRHE for HER to drive 10 mA cm−2 in high-pH media. Upon integration into two electrode electrolysers, the synergetic FeMoSe@NiCo-LDH electrocatalyst delivers a stable cell voltage is 1.71 V (overall seawater splitting) and 1.65 V (overall water splitting), stability at 10 mA cm−2, demonstrating its spectacular bifunctional activity, commendable for the sustainable hydrogen generation. The FeMoSe@NiCo-LDH catalyst exemplifies an economically viable and environmentally sustainable approach for hydrogen generation on larger scale.

Redox Promoted Rapid and Deep Reconstruction of Defect-Rich Nickel Precatalysts for Efficient Water Oxidation.

Understanding the reconstruction mechanism to rationally design cost-effective electrocatalysts for oxygen evolution reaction (OER) is still challenging. Herein, a defect-rich NiMoO4 precatalyst is used to explore its OER activity and reconstruction mechanism. In situ generated oxygen vacancies, distorted lattices, and edge dislocations expedite the deep reconstruction of NiMoO4 to form polycrystalline Ni (oxy)hydroxides for alkaline oxygen evolution. It only needs ≈230 and ≈285mV to reach 10 and 100mA cm-2, respectively. The reconstruction boosted by the redox of Ni is confirmed experimentally by sectionalized cyclic voltammetry activations at different specified potential ranges combined with ex situ characterization techniques. Subsequently, the reconstruction route is presented based on the acid-base electronic theory. Accordingly, the dominant contribution of the adsorbate evolution mechanism to reconstruction during oxygen evolution is revealed. This work develops a novel route to synthesize defect-rich materials and provides new tactics to investigate the reconstruction.

Two-step annealing synthesis of MOF-derived Cr-Co-Ru metallic oxides for improving the oxygen evolution reaction in acidic water splitting

The development of acid-sensitive OER (Oxygen Evolution Reaction) electrocatalysts based on ruthenium oxides is a crucial step toward achieving large-scale hydrogen production in low-cost Proton Exchange Membrane (PEM) electrolyzers. However, a major challenge in this field is to overcome the tendency of ruthenium-based metal oxide dissolving in acidic environments, which affects long-term stability. In this study, we employed MIL-88B(Cr) as a precursor and used a two-step annealing method to prepare trimetallic metal oxides Cr0.5CoxRu0.5-xO2-δ. Detailed experimental measurements demonstrate that the introduction of Co reduced the volume of individual catalyst crystallites without disrupting the rutile crystal structure and inherent activity of CrO2@RuO2. Simultaneously, Co and Cr doping lowered the oxidation state of Ru within the catalyst system. Lower oxidation states of Ru are more stable during the OER reaction, ensuring the stability of this catalyst to be at least 100 hours. Furthermore, Co incorporation raises the energy required for oxygen vacancy formation, reduced the involvement of lattice oxygen, and enhanced the catalyst's activity. The catalyst Cr0.5Co0.17Ru0.33O2-δ with the best performance exhibited the overpotential of only 224 mV at 10 mA cm-2 in 0.5 M H2SO4. This study offers a viable strategy for developing highly active and stable catalysts in acidic media by controlling the electronic structure of RuO2.

Directional electron transport and strong chloridion repulsion enabled by Hierarchical NiCo2O4/NiCoP heterojunction for efficient seawater oxidation

Optimizing the efficiencies of both electron transport and chloridion repulsion are highly desired for achieving high-performance oxygen evolution reaction (OER) electrocatalysts in seawater oxidation, but still remains a huge challenge. In this study, an efficient synthetic method is developed to successfully synthesize a novel heterogeneous hollow polyhedron nanocages (denoted as NiCo2O4/NiCoP) with directional electron transport and strong chloridion repulsion properties, which profits from its diverse work functions and anion electrostatic repulsion in heterojunction nanostructure, respectively. Accordingly, NiCo2O4/NiCoP exhibits superior OER activity in 1 M KOH (η = 325 mV@10 mA cm−2) and alkaline simulated seawater (η = 340 mV@10 mA cm−2), as well as outstanding long-term stability. Density functional theory calculations demonstrate that the construction of NiCo2O4/NiCoP heterojunction promotes the directional electron transport in the heterogeneous interface and enables strong chloridion repulsion in comparison with individual NiCo2O4 and NiCoP, thus largely improving its OER performance in alkaline simulated seawater.

Synthesis of ultrafine Fe-doped Ni3Se4 nanoparticles on tube-like N-doped carbon as a robust electrocatalyst for oxygen evolution reaction

Metal-organic frameworks (MOFs) present a wealth of possibilities for functional materials, courtesy of vast tunable compositions to tailor the physical and chemical properties of their derivatives. In this work, NiFe-BTC(H2SeO3) MOF precursors with varied Fe:Ni ratios are synthesized via a modified hydrogen-bonded organic framework (HOF)-templated strategy. The pre-introduced selenium source in the MOF framework provide the advantages of confined growth of FeNi-selenides during the calcination process. As a result, a highly active and stable, ultrafine Fe-doped Ni3Se4 nanoparticles (4.3 nm) loaded on hollow tube-like N-doped carbon is synthesized as an advanced electrocatalyst for oxgen evolution reaction (OER). Furthermore, the Fe:Ni ratio in catalyst also play a crucial role for efficient electrochemical OER applications. Remarkably, the optimized 2Fe-Ni3Se4@NC catalyst exhibited impressive OER activity with a low overpotential of 272 mV to achieve a current density of 10 cm mA-² and exceptional stability for 110 h at 20 mA cm−2 tested in a 1.0 M KOH solution. This proposed strategy presents a facile approach for the rational design of catalyst composition, and can be extended to prepare other energy conversion and storage materials.

Optimizing the Synergistic Effect of Co and Fe for Efficient and Durable Oxygen Evolution under Alkaline Conditions.

Developing robust oxygen evolution reaction (OER) electrocatalysts is crucial for advancing anion exchange membrane water electrolysis (AEMWE). In this study, we present a catalyst optimizing the synergistic effect of Co and Fe by creating a CoFe-based layer on a Fe-based electrode (Fe@CoFe). The Fe@CoFe exhibits an overpotential of 168 mV at 10 mA cm-2 under half-cell conditions and a current density of 10 A cm-2 at 2 V in the AEMWE system with 1 M KOH. Moreover, it showcases a degradation rate of 76 μV h-1 for 2000 h at 500 mA cm-2 in the single-cell system. This study demonstrates the feasibility of achieving efficient and durable water electrolysis using a transition metal-based catalyst exclusively fabricated via electrodeposition.

Core-bishell NiFe@NC@MoS2 for boosting electrocatalytic activity towards ultra-efficient oxygen evolution reaction

Designing and developing suitable oxygen evolution reaction (OER) catalysts with high activity and stability remain challenging in electrolytic water splitting. Hence, NiFe@NC@MoS2 core-bishell composites wrapped by molybdenum disulphide (MoS2) and nitrogen-doped graphene (NC) were prepared using hydrothermal synthesis in this research. NiFe@NC@MoS2 composite exhibits excellent performance with an overpotential of 288 mV and a Tafel slope of 53.2 mV·dec−1 at a current density of 10 mA·cm−2 in 1 M KOH solution, which is superior to commercial RuO2. NC and MoS2 bishells create profuse edge active sites that enhance the adsorption ability of OOH* while lowering the overall overpotential of the product and improving its oxygen precipitation performance. The density function theory(DFT) analysis confirms that the layered MoS2 in NiFe@NC@MoS2 provides additional edge active sites and enhances electron transfer, thus increasing the intrinsic catalytic activity. This research paves a novel way for developing OER electrocatalysts with excellent catalytic performance.

Phase transitions in NiO during the oxygen evolution reaction assessed via electrochromic phenomena through operando UV–Vis spectroscopy

Due to its high activity and stability, nickel oxide (NiO) has shown significant promise as an electrocatalyst for the alkaline oxygen evolution reaction (OER). In parallel, NiO exhibits a well-known electrochromic phenomenon, changing its optical properties in response to an applied electric potential. This study investigates the relationship between NiO phase changes that occur during the OER and the connected optical modulation using operando UV–visible reflectance spectroscopy. The correlation between the OER activity and the electrochromic behavior of NiO is explored, providing insights into the underlying physicochemical mechanisms governing both phenomena. Strong reduction of the reflected light at higher applied potentials cannot be attributed solely to the change in optical bandgap due to the phase change or the change in the material's refractive index when different phases form. Therefore, in-gap states responsible for increasing the absorption at higher applied potentials were experimentally characterized by ultraviolet photoelectron spectroscopy (UPS) and X-ray absorption spectroscopy (XAS). The results show that phase changes in NiO during OER influence its optical absorption characteristics, which in turn give access to following active phase changes of the electrocatalyst material through a non-invasive, optical, operando probe in real time allowing for kinetic studies of the involved solid-state conversion reactions.