OER Process Research Articles

3D NiCoW Metallic Compound Nano-Network Structure Catalytic Material for Urea Oxidation

Urea shows promise as an alternative substrate to water oxidation in electrolyzers, and replacing OER with the Urea Oxidation Reaction (UOR, theoretical potential of 0.37 V vs. RHE) can significantly increase hydrogen production efficiency. Additionally, the decomposition of urea can help reduce environmental pollution. This paper improves the inherent activity of catalytic materials through morphology and electronic modulation by incorporating tungsten (W), which accelerates electron transfer, enhances the electronic structure of neighboring atoms to create a synergistic effect, and regulates the adsorption process of active sites and intermediates. NiCoW catalytic materials with an ultra-thin nanosheet structure were prepared using an ultrasonic-assisted NaBH4 reduction method. The results show that during the OER process, NiCoW catalytic materials have a potential of only 1.53 V at a current density of 10 mA/cm2, while the UOR process under the same conditions requires a lower potential of 1.31 V, demonstrating superior catalytic performance. In a mixed electrolyte of 1 M KOH and 0.5 M urea, overall water splitting also shows excellent performance. Therefore, the designed NiCoW electrocatalyst, with its high catalytic activity, provides valuable insights for enhancing the efficiency of water electrolysis for hydrogen production and holds practical research significance.

Optimizing cobalt/nickle sulfide heterojunction interface with ordered porous framework for efficient rechargeable zinc-air batteries

Developing efficient oxygen evolution/reduction reaction (OER/ORR) bifunctional catalysts is essential to improve zinc-air batteries (ZABs) performance. In this study, an OER/ORR bifunctional catalyst consists of cobalt and nickel sulfide heterojunction with three-dimensional ordered mesoporous structure is fabricated (3DOM Co9S8/Ni3S4). In-situ attenuated total reflection Fourier transform infrared tests and theoretical calculations reveal that the heterojunction structure promotes electrons transfer from Co9S8 to Ni3S4 and modulates the d-band center, thus optimizing the adsorption/desorption of *OH, *O and *OOH oxygen-containing intermediates and contributing to the improvement of the reactivity of the catalyst. In-situ Raman analysis shows that 3DOM Co9S8/Ni3S4 undergoes surface reconstruction to form highly reactive NiOOH species during the OER process. Meanwhile, the 3DOM framework structure also increases the catalyst specific surface area and benefits the mass transfer process during the reactions. As a result, 3DOM Co9S8/Ni3S4 exhibits a low OER overpotential (334 mV) at 10 mA cm−2 and the ORR half-wave potential is 0.77 V vs. RHE. The rechargeable ZABs with 3DOM Co9S8/Ni3S4 cathode deliver an energy density of 760.73 mAh g−1 at 10 mA cm−2 and stable cycling performance for 100 hours. This study provides guidance for developing efficient heterojunction bifunctional catalysts for ZABs.

Constructing Hydrangea-Like Iron-Cobalt Phosphides via Boron-Assisted Strategy as an Efficient Catalyst for Water Splitting at High Current Density.

Finding suitable bifunctional catalysts for industrial hydrogen production is the key to fully building a hydrogen energy society. In this study, we present a novel approach to modifying the surface morphology of electrodeposited cobalt phosphide (CoP). Specifically, we have developed a method to create a hydrangea-like structure of bimetallic cobalt-iron phosphide (B-CoFeP@CoP) through ion-exchange and NaBH4-assisted strategies. This catalyst exhibited excellent bifunctional catalytic capability at high current densities, achieving a current density of 500 mA cm-2 at a small overpotential (387 mV for OER and 252 mV for HER). When assembled into an OWS electrolyzer, this catalyst showed a fairly low cell voltage (≈1.88 V) at 500 mA cm-2 current density., Furthermore, B-CoFeP@CoP shows ceaseless durability over 120 h in both freshwater and seawater with almost no change in the cell voltage. A combined experimental and theoretical study identified that the unique hydrangea-like structure provided a larger electrochemically active surface area and more effective active sites. Further analysis indicates that during the OER process, phosphides ensure that bimetallic active sites adsorb more OOH * intermediates and further DFT calculations showed that B-Fe2P and B-Co2P acted as active centers for dissociation of H2O and desorption of H2, respectively, to synergistically catalyze the HER process.

Molten salt electrolytic CO2-derived NiCo2@C catalysts with enhanced oxygen evolution reaction

Carbon-based nonprecious metallic electrocatalysts have garnered considerable attention due to their tunable structures, rapid electron transfer, and easy characterization. There is great anticipation for the development of green and controllable methods for metal-carbon-based electrocatalysts. Molten salts synthesis offers a green, facile and effective approach for fabricating carbon-based materials, utilizing carbon dioxide (CO2) as the carbon source. In this study, the co-electroreduction of CO2 and the binary metal oxide NiCo2O4 is carried out in a mixture of Li2CO3, Na2CO3, and K2CO3 at 500oC. This process leads to the formation of metal alloy nanoparticles encapsulated in a carbon matrix derived from CO2, referred to as NiCo2@C. The resulting NiCo2@C exhibits low overpotential and Tafel slope (340mV@10mAcm−2, 67mV dec−1) in 0.1M KOH solution for OER, which is superior to the commercial RuO2 (360mV@10mAcm−2, 88mV dec−1). Both experimental and theoretical findings indicate the synergistic effects of Ni/Co bimetallic sites. Spontaneous adsorption of hydroxide ion on the bridging sites of heterologous diatoms facilitates the adsorption and desorption of intermediates during the OER process.

Axial modulation of catalysis mechanism via charge-asymmetric for enhanced electrocatalytic performance toward hydrogen and oxygen evolution reactions

Designing efficient, stable, and nonprecious metal bifunctional catalysts is warranted for realizing the industrial application of electrocatalytic overall water splitting. Herein, we report a new catalyst (CoFe/SNC) for the HER and OER. The active site of catalysis composed of two charge-asymmetric Co/Fe atoms could axial modulation of the catalysis mechanism, thus improving the kinetics of the HER and OER. Moreover, the use of hollow porous carbon spheres as catalyst support not only enhances the distribution of Co/Fe atoms but also improves the mass transfer during the HER and OER processes. Therefore, the CoFe/SNC displays a good alkaline HER and OER activity with a small overpotential of 96.2 mV and 285.8 mV at 10 mA cm−2, respectively. Theoretical calculations reveal that the Fe atoms with optimal absorption energy for the hydrogen intermediate and the Co centers with a reduced energy barrier for the rate-determining step are the active sites for HER and OER, respectively. Additionally, the synergistic effect of Co/Fe dual-atoms could effectively optimize the intermediate adsorption of Co/Fe-N4 sites and improve the barriers of HER and OER activity and stability. This study provides valuable insight for designing bifunctional alkaline water-splitting electrocatalysts.

Effect of Mo on surface reconstruction of FeCoNi-based high entropy alloy film electrode for oxygen evolution reaction

The selection of elements, tune of compounds types and modification of structure are important ways to improve OER activity of high-entropy alloys. The reconstruction behavior of film electrodes during OER process revealed that Mo element has a strong promoting effect on the reconstruction of FeCoNi-based films. It is shown by first-principles that electron-deficient region could be formed near Mo, and electron-rich region could be formed near surrounding elements of Mo. Charge transfer may be the reason that Mo promotes reconstruction of high-entropy alloys. Compared with FeCoNiCr film electrode, FeCoNiCrMo film electrode, the 2p3/2 binding energy peaks of Fe/Co/Ni in which are shifted forward, has more oxygen-containing species and oxygen vacancies. The study also revealed the existence of lattice oxygen mechanism during OER process. The deposition thickness of alloy film has a linear relationship with sputtering time and deposition rate of FeCoNiCrMo. There is an optimal deposition thickness of FeCoNiCrMo film electrode for OER. FeCoNiCrMo film electrodes have the most excellent OER performance: the overpotential is 268 mV, and the Tafel slope is 57.6 mVdec−1.

Fabrication of SrSnO3/rGO composite via hydrothermal technique as robust electrocatalyst for OER process

Fabrication of SrSnO3/rGO composite via hydrothermal technique as robust electrocatalyst for OER process

Vanadium-doped FeO/NiS nanosheet arrays: Synergistic heterometal doping and heterostructure design for enhanced oxygen evolution catalysis

The quest for high-performance OER electrocatalysts has been a focal point in the field of energy conversion and storage. Despite the promise shown by nickel sulfide-based materials, the enhancement of their catalytic activity through singular strategies has been found to be inadequate for achieving the desired comprehensive performance improvements. In this context, we introduce a novel V-doped FeO/NiS nanosheet array (V-FeO/NiS/NF) synthesized through a synergistic approach involving heteroatom doping and heterostructure engineering. This advanced material exhibits structural integrity, a three-dimensional nanosheet morphology, and superior electrical conductivity, which collectively contribute to its exceptional electrochemical performance. The V-FeO/NiS/NF electrode can reach a current density of 10 mA cm−2 with an impressively low overpotential of 213 mV and sustains its activity for an extended period of 196 hours, surpassing the stability and efficiency of many electrodes. Theoretical insights reveal that vanadium doping significantly lowers the adsorption free energy of key reaction intermediates, thereby facilitating the OER process. This study not only presents a robust and efficient OER electrocatalyst but also paves the way for the design of advanced, cost-effective nickel-based sulfide catalysts through strategic heteroatom incorporation and structural optimization.

Ultrafast fabrication of porous NF/Ni for water splitting in alkaline media

In this study, a rapid hydrogen-bubble template electrodeposition method was employed to synthesize a dual-functional catalyst (NF/Ni) for alkaline water splitting. Physical characterization revealed that a coarsened NF/Ni with a porous structure was obtained, providing an enlarged surface area. In addition, it revealed that the CV activation is beneficial to the formation of Ni-Ni(OH)2 coupling interface, which is responsible for reducing of water dislocation energy barrier and providing a balanced H adsorption energy on the Ni site. Consequently, the overpotential of oxygen/hydrogen evolution reaction at 10 mA cm−2 is 290 and 71 mV. In-situ Raman spectroscopies confirm that the generated NiOOH serves as the active center for OER process. When assembled to a two-electrode cell, it showed a cell voltage of 1.62 V@10 mA cm−2, which was 160 mV lower than that of NF‖NF. Furthermore, the university study confirms the formation of hydroxide on the surface of the metal is beneficial to boosting the hydrogen evolution activity.

Strong electronic interaction in chromium-molybdenum dual incorporated few-layer cobalt sulfide nanosheets with lattice distortion for efficient bifunctional water splitting

The investigation into cost-effective and high-efficiency bifunctional electrocatalysts for electrochemical water splitting is crucial for advancing the conversion efficiency of intermittent energy systems. In this study, a novel dissolution-in situ precipitation method is introduced to synthesize few-layer CoS2 nanosheets incorporating dual cations (Cr, Mo), referred to as Cr/Mo-CoS2. The synergistic influence arising from robust dual dopant-induced coupling interactions and pronounced lattice distortions enhances the rate-determining steps of the HER and OER processes in Cr/Mo-CoS2 by optimizing the adsorption of H* and OOH* intermediates on the catalyst surface. The distinctive pinecone-like structure formed by these nanosheets provides numerous active sites and facilitates electron transfer during reactions. Consequently, the synthesized Cr/Mo-CoS2 nanosheets demonstrate superior catalytic activity, characterized by a low overpotential of 123.8 mV at 10 mA cm−2 for the hydrogen evolution reaction and 310.2 mV at 50 mA cm−2 for the oxygen evolution reaction, coupled with excellent durability in alkaline electrolytes. When utilized as bifunctional electrodes for comprehensive water splitting, Cr/Mo-CoS2 achieves a current density of 10 mA cm−2 at a cell voltage of 1.55 V. This research underscores the critical role of dual-cation doping-induced coupling interactions and significant lattice distortions in augmenting the performance of transition metal chalcogenide electrocatalysts.

Generating highly active oxide-phosphide heterostructure through interfacial engineering to break the energy scaling relation toward urea-assisted natural seawater electrolysis

Urea-assisted natural seawater electrolysis is an emerging technology that is effective for grid-scale carbon–neutral hydrogen mass production yet challenging. Circumventing scaling relations is an effective strategy to break through the bottleneck of natural seawater splitting. Herein, by DFT calculation, we demonstrated that the interface boundaries between Ni2P and MoO2 play an essential role in the self-relaxation of the Ni–O interfacial bond, effectively modulating a coordination number of intermediates to control independently their adsorption-free energy, thus circumventing the adsorption-energy scaling relation. Following this conceptual model, a well-defined 3D F-doped Ni2P-MoO2 heterostructure microrod array was rationally designed via an interfacial engineering strategy toward urea-assisted natural seawater electrolysis. As a result, the F-Ni2P-MoO2 exhibits eminently active and durable bifunctional catalysts for both HER and OER in acid, alkaline, and alkaline seawater-based electrolytes. By in-situ analysis, we found that a thin amorphous layer of NiOOH, which is evolved from the Ni2P during anodic reaction, is real catalytic active sites for the OER and UOR processes. Remarkable, such electrode-assembled urea-assisted natural seawater electrolyzer requires low voltages of 1.29 and 1.75 V to drive 10 and 600 mA cm−2 and demonstrates superior durability by operating continuously for 100 h at 100 mA cm−2, beyond commercial Pt/C ‖ RuO2 and most previous reports.

Synthesis, physical and electrochemical characterization of NiFe2O4/ZnO nanocomposite for OER application

The wide use of conventional fuels is leading to the rise in energy crisis and environmental pollution. The hydrogen fuel can be used as alternative of conventional energy sources to overcome the problem. The hydrogen is obtained from water splitting through oxygen evolution reaction. In the present work, NiFe2O4/ZnO electrocatalyst was prepared by hydrothermal process and grown on nickel foam for OER process. The physical, morphological and elemental analysis of composite was done to execute the crystallinity, surface area and purity of prepared composite. The prepared nanocomposite has high surface area than pure samples. The chronoamperometry analysis was used to assess the enduring stability and durability of synthesized composite. The electrochemical characterization confirmed that composite has low overpotential value (174 mV) and Tafel gradient (33 mV dec−1) with high structural stability. The prepared nanocomposite easily transfers electrons to start OER process. Hence it will perform efficiently for OER and other related applications in future owing to its fine crystalline structure, bulk surface area, low Tafel and overpotential and high stability.

Lattice strain induced rapid structural reconstruction of NiCo hydroxide for efficient water oxidation

In the realm of catalysis, the efficiency of nickel-cobalt (NiCo) based catalysts is hampered by the sluggish kinetics of electrochemical reconstruction. The research herein proposes an innovative strategy centered on the induction of lattice strain to surmount this challenge. We successfully engineer lattice strain and distortion within nickel-cobalt hydroxide by the strategic incorporation of iridium. The X-ray absorption spectroscopy, charge density of elements simulation, ultraviolet photoelectron spectra combined with in-situ Raman results demonstrate that the electronic coupling between iridium and nickel-cobalt is enhanced by lattice strain, which narrows the band gap, and then boosts the electrochemical reconstruction of NiCo hydroxide. Furthermore, the in-situ EIS, methanol oxidation reaction, and DFT calculations collectively indicate that lattice strain can expedite the kinetic adsorption and desorption of intermediates during the OER process. The reconstructed voltage and overpotential are reduced by 50 mV and 77 mV after introducing lattice distortion, and a high stability for more than 500 h, respectively. This unique insight into lattice strain modification provides a way to optimize catalytic functions.

Stirred-electrodeposition construction of porous Fe-doped NiSe nanoclusters as a bifunctional catalyst for water splitting

The electrodeposition method is commonly used for fabricating water splitting catalysts. Traditional methods assume a static precursor solution, ignoring the effects of solution dynamics. We theorized that stirring the solution during electrodeposition could improve mass transfer and current distribution, thereby enhancing electrochemical kinetics and nucleation. Consequently, we developed a novel electrodeposition technique to synthesize Fe-doped NiSe, an effective catalyst for alkaline water hydrolysis, demonstrating exceptional performance and stability. This catalyst notably decreases the overpotentials for OER and HER to 185/266 mV and 101/271 mV at 10 and 300 mA cm−2, respectively. At the same time, the overall water splitting system comprising this catalyst requires only a low potential of 1.48 V to stably catalyze water splitting for over 60 hours. Electrochemical tests indicate that stirred deposition endows the catalyst with a larger electrochemically active area. In-situ Raman spectroscopy reveals NiOOH as an active phase, and Fe doping facilitates NiOOH formation at lower overpotentials, enhancing OER performance. First-principles calculations suggest that Fe doping optimizes the rate-determining step, lowers the activation energy for the OER process, and boosts conductivity. This study presents a method to improve OER efficiency in Ni-based catalysts, offering insights into mechanism control.

Homogeneous In‐Plane Lattice Strain Enabling d‐Band Center Modulation and Efficient d–π Interaction for an Ag2Mo2O7 Cathode Catalyst With Ultralong Cycle Life in Li‐O2 Batteries

AbstractAlthough lithium–oxygen batteries (LOBs) hold great promise as future energy storage systems, they are impeded by insulated discharge product Li2O2 and sluggish oxygen reduction reaction/oxygen evolution revolution (ORR/OER) kinetics. The application of a highly efficient cathode catalyst determines the LOBs performance. The d‐band modulation and catalytic kinetics promotion are important concept guidelines for the performance enhancement of cathode catalysts. In this work, the homogeneous in‐plane distortion‐derived synergistic catalytic capability of an Ag2Mo2O7 catalyst with modulated d‐band centers and promoted ORR/OER kinetics is demontrated. The uniform elongation of Ag─O bonds and compression of Mo─O bonds in (020) plane leads to d‐band splitting and d‐band center optimization and delivers improved adsorption behavior for high ORR/OER capability. Furthermore, the spatial and energy overlap of Ag dxz and O2 anti‐bonding π* orbitals facilitate electron injection during ORR process and reduce the energy barrier for charge transfer and O2 desorption during OER process, accelerating the ORR/OER kinetics. As a result, the (020) plane‐exposed Ag2Mo2O7 cathode exhibits ultralong cycle stability of 817 cycles at 500 mA g−1 and large specific discharge/charge capacities of 15898/15180 mAh g−1. This work provides facile concept guidance for optimizing catalytic capability through controlled lattice distortion in cathode catalysts for LOBs.

Synergistic effect to unlock the activity and stability for oxygen evolution reaction in spinel LiMn2O4 via d-block metal substitution

An effective strategy using d-block metal hybridization was proposed to induce electronic interaction and promote the synergistic effect, aiming to enhance the OER performance of cost-effective spinel LiMn2O4. Indeed, we deployed a series of LiNixMn2-xO4 catalysts substituted with Ni, yielding the increase of Mn valence states from Mn3.5+ to Mn4+. The LiNi0.5Mn1.5O4 catalyst achieved an excellent OER performance in alkaline media, with an overpotential reduction more than 320 mV at 10 mA cm−2 compared to the unsubstituted LiMn2O4, as well as the electrochemical stability. It was shown to be superior to the most reported Mn-based oxides OER electrocatalysts. Theoretical calculations demonstrated that Ni doped holes in the Mn site, leading to an increase in Mn4+, and that the shared covalent network of Ni 3d-O 2p-Mn 3d optimized an easier desorption of intermediates. These results pave a new example for modulating the chemisorption strength, thus enabling activating the activity and stability of OER process for cost-effective electrocatalysts based on spinel Mn oxides.

Stimulus of Work Function on Electron Transfer Process of Intermetallic Nickel-Antimonide Toward Bifunctional Electrocatalyst for Overall Water Splitting.

Engineering the intermetallic nanostructures as an effective bifunctional electrocatalyst for hydrogen and oxygen evolution reactions (HER and OER) is of great interest in green hydrogen production. However, a few non-noble metals act as bifunctional electrocatalysts, exhibiting terrific HER and OER processes reported to date. Herein the intermetallic nickel-antimonide (Ni─Sb) dendritic nanostructure via cost-effective electro-co-deposition method is designed and their bifunctional electrocatalytic property toward HER and OER is unrevealed. The designed Ni─Sb delivers a superior bifunctional activity in 1mKOH electrolyte, with a shallow overpotential of ≈119mV at -10mA for HER and ≈200mV at 50mA for OER. The mechanism behind the excellent bifunctional property of Ni─Sb is discussed via "interfacial descriptor" with the aid of Kelvin probe force microscopy (KPFM). This study reveals the rate of electrocatalytic reaction depends on the energy required for electron and proton transfer from the catalyst's surface. It is noteworthy that the assembled Ni─Sb-90 electrolyzer requires only a minuscule cell voltage of ≈1.46V for water splitting, which is far superior to the art of commercial catalysts.

Rational design of multi-component Fe(OH)3/Ni-NiO heterostructures bifunctional catalyst for electrochemical water splitting

Exploring economic-efficient bifunctional catalysts is critical for the production of green hydrogen through water splitting. Herein, we fabricate a novel hybrid catalyst with three-phase heterojunction (Fe(OH)3/Ni-NiO) via a simple electrodeposition and chemical precipitation method. Benefiting from the desirable amorphous-crystal interfaces, the electronic structure of Ni, NiO and Fe(OH)3 is regulated, which will optimize the adsorption of H intermediates (H*) and also reduce the kinetic barrier for the hydrogen evolution reaction (HER). The optimal Fe(OH)3–3/Ni-NiO/CC shows superior bifunctional activity with low overpotentials of 66 mV for HER and 220 mV for OER at 10 mA cm−2 in alkaline solution, respectively, as well as remarkable durability over a period of 40 h. Besides, Fe(OH)3–3/Ni-NiO/CC requires 1.52 and 1.72 V to deliver 10 and 100 mA cm−2 and shows no obvious increase in current within 40 h toward overall water splitting. Experimental and theoretical results show that the HER process is promoted by the synergistic effect of electronic redistribution between Ni, NiO and Fe(OH)3 due to the construction of three phase crystalline-amorphous heterogeneous interface. Meanwhile, Fe(OH)3 and NiO appeared reconstruction, transforming into FeOOH and NiOOH during OER process, respectively. This work offers a simple synthesis method for designing bifunctional catalysts for water splitting.

Investigation on the reaction mechanism and stability of Ruddlesden-Popper structure Srn+1BnO3n+1 (B=Ru, Ir, n=1, 2) as an oxygen evolution reaction electrocatalyst in acidic medium

R–P structured catalysts have attracted attention due to their low noble metal content and long-term stability. In this paper, we calculated the synthesis difficulty, Sr segregation, and OER catalytic activity of SrBO3, Srn+1BnO3n+1 (B = Ru, Ir, n = 1, 2), taking into account the effects of perovskite layer numbers and strain. The synthesis difficulty was calculated: SrBO3 < Sr2BO4 < Sr3B2O7. The perovskite layer numbers of R–P catalysts were also found to affect the OER process, from n = 1 to 2, the rate-controlling step changes from O*→OOH* to OOH*→O2. Sr2IrO4 was calculated to have the best catalytic activity but is very prone to Sr segregation. Due to the unique layered nature, Sr2IrO4 is still considered the most promising OER catalyst. Furthermore, we also concluded that applying strain impairs the OER catalytic performance of R–P oxides. Our work investigated the OER catalytic mechanisms of R–P oxides, which is significant for the development of water electrolysis.

Al-Ce co-doped BaTiO3 nanofibers as a high-performance bifunctional electrochemical supercapacitor and water-splitting electrocatalyst

Supercapacitors and water splitting cells have recently played a key role in offering green energy through converting renewable sources into electricity. Perovskite-type electrocatalysts such as BaTiO3, have been well-known for their ability to efficiently split water and serve as supercapacitors due to their high electrocatalytic activity. In this study, BaTiO3, Al-doped BaTiO3, Ce-doped BaTiO3, and Al-Ce co-doped BaTiO3 nanofibers were fabricated via a two-step hydrothermal method, which were then characterized and compared for their electrocatalytic performance. Based on the obtained results, Al-Ce co-doped BaTiO3 electrode exhibited a high capacitance of 224.18 Fg−1 at a scan rate of 10 mVs−1, high durability during over the 1000 CV cycles and 2000 charge–discharge cycles, proving effective energy storage properties. Additionally, the onset potentials for OER and HER processes were 11 and − 174 mV vs. RHE, respectively, demonstrating the high activity of the Al-Ce co-doped BaTiO3 electrode. Moreover, in overall water splitting, the amount of the overpotential was 0.820 mV at 10 mAcm−2, which confirmed the excellent efficiency of the electrode. Hence, the remarkable electrocatalytic performance of the Al-Ce co-doped BaTiO3 electrode make it a promising candidate for renewable energy technologies owing to its high conductivity and fast charge transfer.