Oxygen Evolution Activity Research Articles

Ni2+ Ion-Induced Phase and Morphology Tailoring in Nix-CuMoSe Nanorod Catalysts for Overall Water Splitting.

Copper molybdenum-based selenides (CuMoSe) as promising hydrogen evolution catalysts have been widely applied in the electrocatalytic splitting of water, while their limited active sites and relatively poor oxygen evolution activity restrict their further application as effective bifunctional electrocatalysts. Here, we report a simple hydrothermal method to fabricate rodlike NiCuMoSe arrays on nickel foam (Nix-CuMoSe/NF), the morphology of which is determined by Ni2+ ions because Ni2+ can promote the growth of the rodlike structure. Furthermore, the phase transformation from CuSe to CuSe2 is triggered by adjusting the Ni2+ ion content of the growth solution. Due to the morphology control and phase component modulation, the prepared Ni2.5-CuMoSe/NF possesses effective catalytic activities of the hydrogen/oxygen evolution reaction (HER/OER) with overpotentials of 89/183 mV at 10 mA cm-2 in 1 M KOH, and the cell (composed of Ni2.5-CuMoSe/NF as both the cathode and anode) can provide a current density of 10 mA cm-2 at a low cell voltage of 1.50 V with a stability of 110 h. This work will advance the development of transition metal electrocatalysts for effective overall water splitting.

Enhanced photocatalytic hydrogen and oxygen evolution activity by two-dimensional van der Waals AlSb/ZnO heterostructure: A first-principles study

Photocatalytic water splitting facilitates the generation of green hydrogen energy by transforming renewable solar energy into chemical energy. This paper investigated the electronic, optical, and photocatalytic properties of AlSb/ZnO van der Waals (vDW) heterostructure using density functional theory. AlSb/ZnO, a semiconductor heterostructure with an indirect bandgap, was energetically stable with a formation energy of −0.4 eV as well as dynamically and thermally stable. The band edges of the 2D heterostructure maintained the essential redox energy levels for complete water splitting, allowing hydrogen and oxygen generation. Moreover, the heterostructure exhibited a high absorption coefficient in the visible region of the solar spectrum compared to the individual AlSb and ZnO monolayers. We revealed low barrier potential at neutral pH conditions for oxygen and hydrogen evolution reactions from the Gibbs free energy calculation without any external potential. Our study additionally showed the solar-to-hydrogen efficiency of 27.93% and a carrier utilization efficiency of 42.83%, indicating the AlSb/ZnO heterostructure as an excellent water splitting photocatalyst with remarkable potential for fuel cells and energy storage applications.

Increased water splitting activity of self-supported 3D nanoporous Ni and Co-based phosphides prepared by dealloying and electrophoretic deposition

The production of hydrogen by water electrolysis is an essential route to promote hydrogen energy. Design catalysts with plenty of active sites and non-precious metals is the key to realizing hydrogen production by water cracking. We have prepared nanoporous NiCoP using a dealloying method, and deposited the resultant NiCoP on sulfide-treated nickel foam (NF) by electrophoretic deposition to give a nanoporous NiCoP/Ni3S2/NF composite water electrolysis catalyst. The NiCoP–Ni3S2 heterostructure exhibits an abundance of active sites, and the self-supporting structure enhances electron transfer rate, resulting in superior hydrogen evolution reaction (HER) activity and good oxygen evolution reaction (OER) activity using the NiCoP/Ni3S2/NF composite electrode. The associated HER over-potential in a KOH electrolyte was 27 mV with a Tafel slope of 83 mV/dec and a current density of 10 mA/cm2. The OER over-potential was 353 mV at the current density was 100 mA/cm2. The results generated serve to establish a general method for the preparation of high-performance and low-cost self-supported catalysts for water splitting.

High stability cubic perovskite Sr0.9Y0.1Co1-xFexO3-δ oxygen evolution by phase control and electrochemical reconstruction

Transition metal oxides are considered ideal electrocatalyst materials due to their low cost and high intrinsic activity. Among them, SrCoO3-δ has received increasing attention due to its multi-phase structure and tunable electronic properties, though its OER reaction kinetics and catalysis stability are unsatisfactory. Herein, based on a simple one-step solid-state reaction method, we use a small amount of rare earth Y ions (10 %) to transform H-SCO2.52 from a hexagonal structure to a stable cubic perovskite Sr0.9Y0.1CoO3−δ. While broadening the atomic ratio of Co and Fe in the B-site under the cubic perovskite Sr0.9Y0.1Co1-xFexO3−δ (x = 0–1), the relationship between the B-site electronic state, oxygen vacancies, and OER performance has been explored. Sr0.9Y0.1Co0.2Fe0.8O3−δ with a high concentration of oxygen vacancies, exhibits the lowest overpotential of 277 mV and maintains stability at 10 mA cm−2 for 88 h. The valence states of Fe and Co atoms in SYC0.2F0.8 O are optimized (Fe2+∼50.81 %, Co2+∼19.39 %), and the oxygen evolution activity is enhanced by electrochemical reconfiguration to form high-valence Fe and Co ions. Selective leaching of Sr ions via electrochemical surface reconstruction activates FeOOH and CoOOH amorphous layer active sites on the catalyst surface, significantly enhancing reaction kinetics.

Metal Single Atom-Hydroxyl Incorporation in Poly(heptazine imide) to Create Active Sites for Photocatalytic Water Oxidation.

Poly(heptazine imide) (PHI) salts are extensively researched crystalline carbon nitride photocatalysts, but their photocatalytic water oxidation (PWO) performance is scarcely researched because of the difficulty in creating efficient active sites. Interference of metal ion (e.g., Na+ and K+) loss from the PHI salts in their PWO research has hardly been considered. Herein, metal single atom─OH (e.g., Co─OH) groups are incorporated into PHI to create efficient PWO active sites, via simple ion metathesis, hydrolysis, and deprotonation. The Co─OH modified PHI exhibits 9.3-fold higher PWO (oxygen evolution) activity than PHI, with an external quantum yield reaching 0.44% even at 600 nm. Excluding interference of the metal ion loss, the function of the Co─OH incorporation is evidenced mainly to facilitate the oxygen evolution reaction, as well as to promote photogenerated charge separation and raise visible light absorption, with the role of the OH especially revealed. Moreover, it is discovered that Na+ loss from sodium PHI will decrease its PWO activity, protonation of PHI has a detrimental effect on its PWO performance, and some other metal single atom─OH incorporation in PHI can also enhance its PWO activity. Overall, this work provides a general way to create PWO active sites in PHI.

Hydrothermal-Induced Cationic Vacancies in NiAl Hydroxide for Enhanced Oxygen Evolution Activities through Optimization of eg* Band Broadening.

Nickel-based hydroxides [Ni(OH)2] have attracted significant attention as effective oxygen evolution reaction (OER) catalysts. In recent years, defect engineering has been extensively utilized in Ni(OH)2 modification research. Numerous studies have confirmed that the generation of defects can expose more active sites and regulate electronic states, particularly through the introduction of Al cationic vacancies, which enhance conductivity and thereby improve the catalytic performance. The traditional method for producing cationic vacancies is electrochemical etching. However, this method generates a limited number of vacancies in the catalysts and has the complex etching process. Herein, we found that when NiAl layered double hydroxides were treated using a hydrothermal process at 100 °C in a KOH solution, more Al cationic vacancies were generated. Compared to the traditional method with an Al leaching efficiency of 24%, our proposed method achieved an Al leaching efficiency of 44%. Meanwhile, the electrochemical results showed that the overpotential was reduced by 110 mV at 10 A/g. Further experiments showed that the enhanced OER activities resulting from an increased number of cationic defects lead to structural distortions, which broaden the eg* band, significantly affecting the rate of electron transfer between the electrocatalyst and external circuitry, thereby enhancing the OER activity. This work presents a promising approach to creating cationic defects in Ni(OH)2 for high-performance electrocatalysts.

I3‐‐Mediated Oxygen Evolution Activities to Boost Rechargeable Zinc‐Air Battery Performance with Low Charging Voltage and Long Cycling Life

An effective strategy to facilitate oxygen redox chemistry in metal‐air batteries is to introduce a redox mediator into the liquid electrolyte. The rational utilization of redox mediators to accelerate the charging kinetics while ensuring the long lifetime of alkaline Zn‐air batteries is challenging. Here, we apply commercial acetylene black catalysts to achieve an I3‐‐mediated Zn‐air battery by using ZnI2 additives that provide I3‐ to accelerate the cathodic redox chemistry and regulate the uniform deposition of Zn2+ on the anode. The Zn‐air battery performs an ultra‐long cycle life of over 600 h at 5 mA cm‐2 with a final charge voltage of 1.87 V. We demonstrate that I‐ mainly generates I3‐ on the surface of carbon catalysts during the electrochemically charging process, which can further chemically react with OH‐ to generate oxygen and further revert to I‐, thus obtaining a stable electrochemical system. This work offers a strategy to simultaneously improve the cycling life and reduce the charging voltage of Zn‐air batteries through redox mediator methods.

I3 --Mediated Oxygen Evolution Activities to Boost Rechargeable Zinc-Air Battery Performance with Low Charging Voltage and Long Cycling Life.

An effective strategy to facilitate oxygen redox chemistry in metal-air batteries is to introduce a redox mediator into the liquid electrolyte. The rational utilization of redox mediators to accelerate the charging kinetics while ensuring the long lifetime of alkaline Zn-air batteries is challenging. Here, we apply commercial acetylene black catalysts to achieve an I3 --mediated Zn-air battery by using ZnI2 additives that provide I3 - to accelerate the cathodic redox chemistry and regulate the uniform deposition of Zn2+ on the anode. The Zn-air battery performs an ultra-long cycle life of over 600 h at 5 mA cm-2 with a final charge voltage of 1.87 V. We demonstrate that I- mainly generates I3 - on the surface of carbon catalysts during the electrochemically charging process, which can further chemically react with OH- to generate oxygen and further revert to I-, thus obtaining a stable electrochemical system. This work offers a strategy to simultaneously improve the cycling life and reduce the charging voltage of Zn-air batteries through redox mediator methods.

N, S, P co-doped Co/Co3O4/C particles on carbon fiber paper as a self-supported bifunctional catalyst for direct seawater splitting

To optimize the distribution and transportation of electrical energy, converting surplus or low-quality electricity through electrocatalytic seawater splitting to produce hydrogen is an ideal method. In this work, we developed a bifunctional electrocatalyst (ZIF-9/CP-S-P) through the in-situ growth of ZIF-9 on the carbon fiber paper (CP), followed by sequential sulfurization and phosphidation. This catalyst achieves stable hydrogen and oxygen production in natural seawater, displaying outstanding oxygen evolution activity with an overpotential of just 390mV at 10mA/cm² (Tafel slope: 426.5mV/dec) and impressive hydrogen evolution activity with an overpotential of only 578mV at 10mA/cm² (Tafel slope: 287.7mV/dec). The two-electrode electrolyzer assembled by ZIF-9/CP-S-P || ZIF-9/CP-S-P was conducted the chronoamperometry test for 20000s in 1M phosphate buffer solution and for 100000s in natural seawater, and its performance was comparable to that of commercial Pt/C || IrO2. These findings indicate the potential of ZIF-9/CP-S-P catalyst for practical applications in direct seawater splitting to produce hydrogen and oxygen.

Full‐Spectrum Light‐Harvesting Solar Thermal Electrocatalyst Boosts Oxygen Evolution

AbstractEnabling high‐efficiency solar thermal conversion (STC) at catalytic active site is critical but challenging for harnessing solar energy to boost catalytic reactions. Herein, we report the direct integration of full‐spectrum STC and high electrocatalytic oxygen evolution activity by fabricating a hierarchical nanocage architecture composed of graphene‐encapsulated CoNi nanoparticle. This catalyst exhibits a near‐complete 98 % absorptivity of solar spectrum and a high STC efficiency of 97 %, which is superior than previous solar thermal catalytic materials. It delivers a remarkable potential decrease of over 240 mV at various current densities for electrocatalytic oxygen evolution under solar illumination, which is practically unachievable via traditionally heating the system. The high‐efficiency STC is enabled by a synergy between the regulated electronic structure of graphene via CoNi‐carbon interaction and the multiple absorption of lights by the light‐trapping nanocage. Theoretical calculations suggest that high temperature‐induced vibrational free energy gain promotes the potential‐limiting *O to *OOH step, which decreases the overpotential for oxygen evolution.

Hierarchical MoO2@MoS2 heterojunction nanosheets anchored with metal-organic framework-derived CoFe alloy as bifunctional catalysts for flexible zinc-air batteries

Crafting a robust, high-performance, non-precious metal-based flexible air electrode is crucial for realizing flexible zinc-air batteries (ZABs). Herein, hierarchical MoO2 and MoS2 heterojunction nanosheets grown on carbon cloth (CC) are prepared through a simple hydrothermal reaction followed by calcination. Afterward, through self-assembly and high-temperature carbonization of zeolitic imidazolate framework-67 (ZIF-67) and Materials of Institute Lavoisier-101 (MIL-101) on the heterojunction nanosheets, a hierarchical structure of nitrogen-doped carbon (NC) encapsulated CoFe alloy nanoparticles (NPs) supported on MoO2@MoS2 heterojunction nanosheets (CC/MoS2@MoO2@CoFe) is obtained. It exhibits remarkable activity and durability for both bifunctional oxygen evolution and reduction reactions (OER/ORR), attributed to the ternary heterojunction formed by NC-coated CoFe alloy NPs uniformly dispersed among the MoO2@MoS2 nanosheets, along with oxygen vacancies at heterogeneous interfaces between MoS2, MoO2, and Co0.72Fe0.28 alloy. As a binder-less self-supporting electrode, the assembled aqueous ZAB demonstrates a maximum power density of 113.6 mW cm–2, surpassing that of Pt/C + RuO2 (75.2 mW cm–2), along with excellent cycling stability. Furthermore, the CC/MoS2@MoO2@CoFe-based flexible ZABs achieve a maximum power density of 54.1 mW cm–2, exhibit good cycling stability for up to 120 cycles, and show outstanding flexibility. This study paves the way for the practical integration of flexible ZABs into wearable electronic devices, heralding a new era of portable power solutions.

Octahedral Co2+‐O‐Co3+ in Mixed Cobalt Spinel Promotes Active and Stable Acidic Oxygen Evolution

AbstractCobalt (Co)‐based oxides show promising activity as precious metal‐free catalysts for the oxygen evolution reaction in proton exchange membrane water electrolysis, but the dissolution of Co has limited the durability of Co3O4 at industrially relevant current densities. This work demonstrates that cation in an octahedral coordination environment accounts for the oxygen evolution activity. Using a mixed inverse‐normal phase spinel CoxGa(3‐x)O4 as a proof‐of‐concept example, the designed Co2+‐O‐Co3+ motifs in octahedral sites trigger oxygen evolution through a kinetically favorable radical coupling pathway. Furthermore, lattice oxygen exchange, a leading factor in catalyst structural degradation for normal Co3O4, is suppressed, as evidenced by isotopic labeling experiments and theoretical calculations. With the optimized catalyst, Co1.8Ga1.2O4, an overpotential of 310 mV at 10 mA cm−2 is reported, with stable operation at 200 mA cm−2 for 200 h in a three‐electrode setup, and a proton exchange membrane electrolyzer operating at 200 mA cm−2 for 450 h.

Ni-CoS2 nanoparticles loaded on 3D RGO for efficient electrochemical hydrogen and oxygen evolution reaction

The development of efficient non-precious metal electrocatalysts for electrochemical water splitting is still a huge challenge. In this study, we designed and synthesized an efficient electrocatalyst for Ni-doped cobalt sulfide supported on 3D RGO (Ni-CoS2/3D RGO) using a simple one-step solvent-thermal method. Ni doping adjusted the charge distribution on the surface of the material, significantly improved the catalytic activity, and then accelerated the reaction kinetics. The high specific surface area and high stability of 3D RGO greatly improved the intrinsic activity of the material, making Ni-CoS2/3D RGO exhibit superior catalytic activity in both electrochemical hydrogen evolution and oxygen evolution. We evaluated the morphology and properties of the catalysts through a series of characterization methods and electrochemical performance tests. When the current density is 10 mA cm−2, the HER overpotential of Ni-CoS2/3D RGO under acidic condition reaches 138 mV, and the Tafel slope is 61 mV dec−1. Under alkaline conditions, the OER overpotential reaches 286 mV, and the Tafel slope is only 48 mV dec−1. And the OWS overpotential of the catalyst is 1.41 V and 1.82 V under acidic and alkaline conditions, respectively, indicating that the catalyst has ideal water splitting performance. This work provides a new idea for the application of 3D reduced graphene oxide in electrochemical direction, and also provides a new strategy for the design and preparation of non-precious metal catalysts for the efficient electrochemical water splitting.

Enhanced Oxygen Evolution Activity at Amorphous Hydroxide/Perovskite Interfaces

Enhanced Oxygen Evolution Activity at Amorphous Hydroxide/Perovskite Interfaces

Oxygen evolution over Fe1/NiSe2 single-atom electrocatalyst: The role of thermal-electrical cascade and surface reconstruing

Oxygen evolution reaction (OER) in water electrolysis is a tough challenge. Here we report the thermally activated on-surface oxygen evolution at nickel diselenide under alkaline conditions, specifically focusing on the (101) and (100) facets supported with Fe single-atom electrocatalysts. Assisted by heat, the Fe1/NiSe2(101) and (100) facets demonstrate highly efficient activity for oxygen evolution at pH = 14. First-principles calculations and AIMD simulations illustrate excellent electrical conductivity and thermal stability of the Fe1/NiSe2(101) and (100) facets, as well as provide a promising understanding of electron transports among the oxygen-containing active species and the electrocatalysts during thermal-electrical cascade of OER under alkaline conditions. The enhanced OER performance depends on the co-adsorbate combinations: *O(Fe-SeⅠ)-*OH(SeⅡ) and *O(Fe-SeⅠ)-*OH(Ni) at the Fe1/NiSe2(101) facet, whose adsorption behaviors lead to self-activated surface reconstruing. Impressively, the affinity of the key intermediates at the potential-determining steps of OER: *O(Fe-SeⅠ) at the Fe1/NiSe2(101) facet, *O(Fe) and *OOH(Fe) at the Fe1/NiSe2(100) facet, is optimized by such self-activated surface reconstruing.

Tailoring Ni-Fe-B Electronic Effects in Layered Double Hydroxides for Enhanced Oxygen Evolution Activity.

NiFe layered double hydroxides (LDHs) are state-of-the-art catalysts for the oxygen evolution reaction (OER) in alkaline media, yet they still face significant overpotentials. Here, quantitative boron (B) doping is introduced in NiFe LDHs (ranging from 0% to 20.3%) to effectively tailor the Ni-Fe-B electronic interactions for enhanced OER performance. The co-hydrolysis synthesis approach synchronizes the hydrolysis rates of Ni and Fe precursors with the formation rate of B─O─M (M: Ni, Fe) bonds, ensuring precise B doping into the NiFe LDHs. It is demonstrated that B, as an electron-deficient element, acts as an "electron sink" at doping levels from 0% to 13.5%, facilitating the transition of Ni2+ to the active Ni3+δ, thereby accelerating OER kinetics. However, excessive B doping (13.5-20.3%) effectively generates oxygen vacancies in the LDHs, which increases electron density at Ni2+ sites and hinders their transition to Ni3+δ, thereby reducing OER activity. Optimal OER performance is achieved at a B doping level of 13.5%, with an overpotential of only 208mV to reach a current density of 500mA cm-2, placing it among the most effective OER catalysts to date. This Ni-Fe-B electronic engineering opens new avenues for developing highly efficient anode catalysts for water-splitting hydrogen production.

Influence of Fe Ions on Anode Performance and the Mechanism of Action during Copper Electrowinning Process.

The performance of the anode varies from the impurity ions in the copper electrowinning process. This work focused on the variation of the electrochemical behavior of the Pb-0.06%Ca-1.2%Sn anode as the Fe ions (Fe3+ and/or Fe2+) existed in the electrolyte by electrochemical characterization. Copper electrodeposition experiments were conducted under a current density of 300 A/m2, with the Fe ion concentration in the electrolyte controlled within the range of 0 to 20 g/L and the Cu ion concentration maintained at 45 g/L at a temperature of 45 °C. The variation in the corrosion resistance, catalytic activity, and structural composition of the anode film layer was analyzed in-depth according to the presence of Fe ions. The results show that the structure of PbO2 on the surface of the film was changed as Fe ions doped into the anode film, and the oxygen evolution activity of the anode was also improved. However, the corrosion resistance decreased with increasing Fe3+ concentration. Furthermore, the addition of 2 g/L Fe2+ in the electrolyte containing 2 g/L Fe3+ led to an elevation in the corrosion resistance of the anode to some extent and further increased the oxygen evolution activity.

Catalyst–Support Interaction in Polyaniline-Supported Ni3Fe Oxide to Boost Oxygen Evolution Activities for Rechargeable Zn-Air Batteries

HighlightsNi3Fe oxide, with an average size of 3.5 ± 1.5 nm, was successfully deposited onto polyaniline (PANI) support through a solvothermal strategy followed by calcination.The catalyst–support interaction between Ni3Fe oxide and PANI can enhance the Ni-O covalency via the interfacial Ni-N bond.Ni3Fe oxide/PANI-assembled Zn-air batteries achieve superior cycling life for over 400 h at 10 mA cm−2 and a low charge potential of around 1.95 V.

Soft chemistry-derived Al-substituted hydrated nickel hydroxide electrodes for rechargeable aqueous batteries.

Hydrated nickel hydroxides with partial aluminum substitution were synthesized using the conventional coprecipitation and soft chemistry methods. The soft chemistry derived sample showed better reversibility owing to the low activity for oxygen evolution during charging. Operando X-ray diffraction indicated the increased interlayer distance and decreased crystallinity during discharging caused by water accommodation.

Guided Heterostructure Growth of CoFe LDH on Ti3C2Tx MXene for Durably High Oxygen Evolution Activity.

Heterostructures of layered double hydroxides (LDHs) and MXenes have shown great promise for oxygen evolution reaction (OER) catalysts, owing to their complementary physical properties. Coupling LDHs with MXenes can potentially enhance their conductivity, stability, and OER activity. In this work, a scalable and straightforward in situ guided growth of CoFeLDH on Ti3C2Tx is introduced, where the surface chemistry of Ti3C2Tx dominates the resulting heterostructures, allowing tunable crystal domain sizes of LDHs. Combined simulation results of Monte Carlo and density functional theory (DFT) validate this guided growth mechanism. Through this way, the optimized heterostructures allow the highest OER activity of the overpotential = 301mV and Tafel slope = 43mV dec-1 at 10mA cm-2, and a considerably durable stability of 0.1% decay over 200h use, remarkably outperforming all reported LDHs-MXenes materials. DFT calculations indicate that the charge transfer in heterostructures can decrease the rate-limiting energy barrier for OER, facilitating OER activity. The combined experimental and theoretical efforts identify the participation role of MXene in heterostructures for OER reactions, providing insights into designing advanced heterostructures for robust OER electrocatalysis.