Oxygen Evolution Reaction Properties Research Articles

Heterojunction of the CoMn Metal–Organic Framework with Lanthanum for Enhanced Oxygen Evolution Reaction

Surface and interfacial electron transfer tends to be the rate-limiting step in multiple electron electrocatalytic reactions such as oxygen evolution reaction (OER). Constructing a heterojunction structure is an effective approach to strengthen the processes. Here, CoMnLax-MOF/CF has been synthesized via a one-pot solvothermal pathway to integrate the charge transport advantage of the heterojunction and the mass-transfer superiority of high porosity of the metal–organic framework (MOF), wherein the heterojunction is formed by introducing La in preparing the CoMn-MOF process. The results demonstrate that the as-prepared CoMnLax-MOF/CF possesses flower-like/flower-bud microstructures with a CoMn-MOF/La-MOF heterojunction topology, resulting in superior OER performance. The enhanced OER property originates from reduced charge-transfer resistance and an enlarged activated surface area. At a molar ratio of nLa:nCo:nMn = 0.2:1:1, the CoMnLa0.2-MOF/CF presents optimal performance. In 1 M KOH, the overpotential is only 201 mV to reach 10 mA cm–2 current density. There appears no significant current density degeneration in the 25 h stability test. This work demonstrates one facile pathway for directly building the heterojunction in CoMn-MOF to achieve superb OER activity.

Promoting surface reconstruction of NiFe layered double hydroxides via intercalating [Cr(C2O4)3]3− for enhanced oxygen evolution

Rationally manipulating surface reconstruction of catalysts for water oxidation, inducing formation and dynamic accumulation of catalytically active centers still face numerous challenges. Herein, the introduction of [Cr(C2O4)3]3− into NiFe LDHs by intercalation engineering to promote surface reconstruction achieves an advanced oxygen evolution reaction (OER) activity. In view of the weak electronegativity of Cr3+ in [Cr(C2O4)3]3−, the intercalation of [Cr(C2O4)3]3− is expected to result in an electron-rich structure of Fe sites in NiFe LDHs, and higher valence state of Ni can be formed with the charge transfer between Fe and Ni. The optimized electronic structure of NiFe-[Cr(C2O4)3]3−-LDHs with more active Ni3+ species and the expedited dynamic generation of Ni3+(Fe)OOH phase during the OER process contributed to its excellent catalytic property, revealed by in situ X-ray absorption spectroscopy, Raman spectroscopy, and quasi-in situ X-ray photoelectron spectroscopy. With the modulated electronic structure of metal sites, NiFe-[Cr(C2O4)3]3−-LDHs exhibited promoted OER property with a lower overpotential of 236 mV at the current density of 10 mA cm−2. This work illustrates the intercalation of conjugated anion to dynamically construct desired Ni3+ sites with the optimal electronic environment for improved OER electrocatalysis.

Polyol Synthesis of Ni and Fe Co-Incorporated Tungsten Oxide for Highly Efficient and Durable Oxygen Evolution Reaction

The development of inexpensive transition metal-based catalysts for water splitting has attracted global attention, which should be accomplished in the simplest and most scalable way feasible. In this study, nickel and iron co-incorporated tungsten oxides (NixFe1-xWO4) were synthesized using a simple polyol method, and the materials achieved a highly efficient and stable oxygen evolution reaction (OER) in an alkaline electrolyte. The product as-synthesized using the polyol method consisted of an undeveloped wolframite structure, which was converted to its complete crystal by heat treatment at 600 °C, with an increase in crystallite size. The OER properties of NixFe1-xWO4 could be controlled by the ratio of Ni and Fe present and heat treatment temperature. A ternary tungsten oxide (Ni0.5Fe0.5WO4) with a Ni:Fe:W molar ratio of 0.5:0.5:1 deposited on a glassy carbon electrode required 297 mV to reach a current density of 10 mA cm−2 in 1.0 M KOH solution. The 10 mA cm−2 electrolysis with the electrode was continued for at least 100 h. This was quite different from a similarly-synthesized NiFe oxide without W, which required an additional 47-mV overpotential to reach 10 mA cm−2 and had inferior durability.

NiCo-BDC derived Co3+ enriched NiCoxOy/NF nanosheets for oxygen evolution reaction

In recent years, transition metal catalysts due to their low price, excellent conductivity and high activity have been extensively studied in OER. It is worth noting that Co3+ plays a vital role in the process of oxygen evolution catalysis, because Co3+ ions are considered to be active sites. The development of catalysts with high Co3+ content has important application prospects for improving water oxidation efficiency. This paper uses a simple ligand-assisted synthesis method to promote the transformation of two-dimensional layered double hydroxides (LDHs) into two-dimensional metal organic frameworks (MOFs). MOF-OH/NF are quickly and easily prepared by electrooxidation, which exhibit superior OER properties, with a low overpotential of 260 mV and 420 mV for the oxygen evolution reaction (OER) at 100 mA cm−2 and 1000 mA cm−2. Moreover, the MOF-OH/NF has good stability in 1.0 M KOH electrolyte solution. This study provides a new idea for the design and synthesis of novel composite electrocatalysts.

Mn 2 V 2 O 7 spiked ball‐like material as bifunctional oxygen catalyst for zinc‐air batteries

Hierarchical micro/nanostructures are believed to be magnificent electrocatalyst materials capable of competing with noble metals and the most expensive catalyst materials for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, Mn2V2O7-based hierarchical spiked ball structures (MVO SBs) were synthesized using a simple hydrothermal technique as a bifunctional oxygen catalyst for rechargeable Zn-air batteries. The linear sweep voltammetry by a rotating disc electrode was used to investigate the ORR and OER properties and their mechanisms, and the charge transfer mechanism was also studied by electrochemical impedance spectroscopy analysis. When compared with platinum with carbon black (Pt/C), the MVO SB catalyst material exhibited comparable ORR and OER properties. Furthermore, the MVO SB material revealed a 4e− transfer pathway in an electrolyte solution. Furthermore, the prepared MVO SB material demonstrated a lower charge-discharge voltage gap when compared with Pt/C material, which is lower than 180 mV at 45 mA cm−2. The cycling test result of MVO SB catalyst sample revealed excellent cycling stability over 50 charging and discharging cycles (~800 min) than the Pt/C sample (30 cycles [~520 min]). The good catalytic activity and excellent structural stability of the MVO SB material are especially due to the more active sites enhanced by the unique spiked ball-like morphology and high specific surface area (11.70 m2 g−1) properties. The achieved results suggest that the synthesized catalyst material could be employed as an oxygen catalyst material for rechargeable Zn-air batteries.

Metal-organic framework interface engineering for highly efficient oxygen evolution reaction

Metal-organic frameworks (MOFs) with intrinsically porous structures and well-dispersed metal sites are promising candidates for the oxygen evolution reaction (OER). However, the practical applications of MOFs for OER are significantly constrained due to their poor charge transfer property and insufficient inherent activity. Herein, we utilized caffeic acid as a bridging agent to covalently bond FeNi-MOF with NiMoO4 in order to tune the charge transfer properties for efficient OER. The optimized organic-inorganic heterocatalyst demonstrates superior OER performance with a low overpotential of 256 mV at a current density of 10 mA cm−2 and long-term stability, outperforming the benchmark IrO2 catalyst and single counterparts. Both experimental and theoretical results indicate that electrons can be transferred from FeNi-MOF to NiMoO4 via a caffeic acid bridging agent, which improves not only the electrical conductivity but also the adsorption capacity of OH– intermediates on MOFs. Therefore, the enhanced OER activity of the heterocatalyst is attributed to the synergistic effects of the multi-components. This study paves the way for the rational design of MOFs-based heterostructures towards efficient electrocatalytic oxygen evolution.

Simultaneous electrical and defect engineering of nickel iron metal-organic-framework via co-doping of metalloid and non-metal elements for a highly efficient oxygen evolution reaction

Metal-organic frameworks (MOFs) are promising electrocatalysts for oxygen evolution reaction (OER) due to their large amounts of active sites reacting with water molecules and desired adsorption/desorption characteristics with oxygen intermediate. However, the intrinsically low electrical conductivity of MOFs hinders their commercialization for the highly efficient OER catalyst. Here, we report 2D morphological NiFe MOF electrocatalyst co-doped with metalloid and non-metal elements for the enhanced OER performances. Te metalloid incorporation on MOFs facilitates electron transfer from transition metals of MOFs to embedded metalloids, which improves OER kinetics enabling favorable adsorption of oxygen intermediate on the surface of the electrocatalyst. Incorporated halogen Cl element could effectively induce defects on MOF as leach out from the surface of electrocatalyst during OER, allowing more active sites exposed to reactants. With the synergistic effect of metalloid (Te) and halogen (Cl) doping on NiFe MOF, the Te and Cl co-doped NiFe MOF growth on Ni foam (NF) present an excellent OER property requiring low overpotential for 224 mV at 30 mA cm−2 in alkaline condition and long-term stability over 120 h.

Mixed B-site ruddlesden-popper phase Sr2(RuxIr1-x)O4 enables enhanced activity for oxygen evolution reaction

Development of high performance electrocatalysts for oxygen evolution reaction (OER) in acidic media remains a challenge for direct water splitting using an electrolyzer. Recently, Ruddlesden-Popper phase Sr2IrO4 was discovered to be an efficient OER catalyst because of its unique structure, which consists of layers of both rock salt and perovskite phases simultaneously. In this study, we prepared a series of B-site mixed, Ruddlesden-Popper phase of Sr2(RuxIr1−x)O4 and examined their electrocatalytic properties for OER in acidic media. Through partial substitution of Ru in the B-site of Ruddlesden-Popper phase materials, we achieved much enhanced OER performance for this series of Sr2(RuxIr1−x)O4 electrocatalysts, among which Sr2(Ru0.5Ir0.5)O4 exhibited the best catalytic activity with a current density of 8.06 mA/cm2 at 1.55 V and a Tafel slope of 47 mV/dec. This current density is three times higher than that of Sr2IrO4. The B-site mixed Sr2(Ru0.5Ir0.5)O4 retained good stability in acidic conditions for > 24 h at 10 mA/cm2. A range of techniques were used to characterize the crystal and electronic structures of the Sr2(RuxIr1−x)O4 samples. Our data indicate that the improved OER performance can be correlated to the formation of high level of hydroxyl groups and the enhanced overlap between Ir/Ru 4d and O 2p orbitals, revealing a new way for the design of efficient OER electrocatalysts by regulating their composition and electronic structures.

Surface facets dependent oxygen evolution reaction of single Cu2O nanoparticles

Understanding and establishing the structure-activity relation of nanoparticles is a prerequisite for rational design of high-performance electrocatalysts. Cu 2 O nanoparticles enclosed with different crystal facets, namely, o-Cu 2 O NPs with {111} facets, c-Cu 2 O NPs with {100} facets are prepared and their electrocatalytic properties for oxygen evolution reaction (OER) in alkaline condition are evaluated at single nanoparticle level with a combination of scanning electrochemical cell microscopy and scanning electron microscopy. It is found that the o-Cu 2 O NPs have significantly superior OER electrocatalytic activity compared to c-Cu 2 O, which is almost inert. The estimated turnover frequency (TOF) at 1.97 V vs. RHE on {111} facet increases from 4 s −1 to 115 s −1 with the octahedron edge length decreasing from 1.3 µm to 100 nm. Deposition of carbon on c-Cu 2 O surface barely promotes the activity, suggesting the inherent poor electric conductivity within the nanocrystal is most likely the reason for low activity. This work provides direct probing to single transition metal oxide crystals with dramatically different activity. We endeavor to directly establish the correlation between nanoparticle surface facets with the intrinsic electrocatalytic OER activity from electrochemical measurement at single Cu 2 O nanoparticles using a combination of SECCM and SEM.

Tuning the interfacial electronic coupling of NiO via CeO2 and nitrogen co-decoration for highly efficient oxygen evolution reaction

• CeO 2 and nitrogen co-decoration are proposed to boost the OER activity of NiO. • The strong electron coupling among Ce/N-NiO can induce the rich Ni 3+ surface. • The surface electron reconfiguration energetically promotes the adsorption of OH – . • Ce/N-NiO shows superior OER property with a low overpotential of 250 mV. • The OER activity of Ce/N-NiO outstrips RuO 2 at high current density. Nickel oxide (NiO) has emerged as a promising electrocatalyst for oxygen evolution reaction (OER) catalysis but undergoes insufficient active sites and unfavorable OH – adsorption properties. Herein, we develop an effective CeO 2 and nitrogen co-decoration strategy to boost the OER performance of NiO (Ce/N-NiO) nanoparticles dramatically. The strong electron coupling among Ce/N-NiO nanoparticles provide exceptional facilities for the interface electron transfer from nitrogen-doped NiO to CeO 2 , and further induces the formation of rich Ni 3+ surface, endowing it with abundant active sites. Besides, the surface electron reconfiguration energetically promotes the adsorption of OH – , resulting in fast reaction kinetics. As expected, the Ce/N-NiO sample shows superior OER property with a low overpotential of 250 mV at 10 mA cm −2 . Particularly, when the current density exceeds 90 mA cm −2 , the OER activity of Ce/N-NiO outstrips noble-metal-based RuO 2 . This co-decoration approach provides a practical guide for designing high-performance catalysts for OER and beyond.

Nickel oxide nanoparticles dispersed on biomass–derived amorphous carbon/cobalt silicate support accelerate the oxygen evolution reaction

The development of robust, low–cost and efficient oxygen evolution reaction (OER) electrocatalysts, especially non–noble–metal–based OER catalysts, is of great significance and imperative to address the energy crisis, but remain challenging. Herein, a biomass–derived three–dimensional (3D) porous carbon/cobalt silicate (C/Co2SiO4) architecture is developed as a support for loading nickel oxide (NiOx) species to prepare an earth–abundant and non–noble–metal–based NiOx/C/Co2SiO4 electrocatalyst. The NiOx nanoparticles are dispersed on 3D C/Co2SiO4 support and the introduction of NiOx species improves the OER active sites and shows the bimetal (Co, Ni) synergetic effect. The NiOx/C/Co2SiO4 electrocatalyst exhibits the overpotential with 355 mV at 10 mA cm−2, Tafel slope with 40 mV dec−1 and large electrochemical active surface areas (ECSA), which are superior to C/Co2SiO4 support and NiOx. The catalytic properties achieved herein are superior or comparable to most transition metal oxides/hydroxides. The findings reveal that the introduction of NiOx nanoparticles can greatly boost the OER property of C/Co2SiO4 support. This work not only develops a non–noble–metal–based NiOx/C/Co2SiO4 catalyst, but also verifies that the introduction of metal oxide species on biomass–derived 3D C/Co2SiO4 provides a new horizon to explore economical, high–efficient and robust OER catalysts.

Three-dimensional hierarchical graphitic carbon encapsulated CoNi alloy/N-doped CNTs/carbon nanofibers as an efficient multifunctional electrocatalyst for high-performance microbial fuel cells

A novel Co/Ni metal-organic framework (MOF)-derived three-dimensional (3D) nanoarchitecture in which graphene carbon-coated CoNi alloy nanoparticles grow on the tips of N-doped carbon nanotubes that are vertically-aligned on carbon nanofibers (Co/Ni@GC/NCNTs/CNFs) is fabricated. The Co/Ni@GC/NCNTs/CNFs electrode has a half-wave oxygen reduction reaction (ORR) potential of 0.80 V, a superior standing stability with 84.8% current retention after 175 000 s. The oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) reach a lower overpotential of 0.395 V and 0.15 V, respectively. Moreover, the resultant sample is an air cathode catalyst in a microbial fuel cell and indicates an utmost power density of 2100 ± 45 mW cm −2 , which is much better than that of the Pt/C electrode (1334 ± 61 mW m −2 ). The density functional theory calculation demonstrates that the designed Co/Ni@GC/NCNTs/CNFs catalyst can remarkably promote OER, ORR, and HER performance. • Co/Ni MOF-derived graphene carbon-coated CoNi alloy/NCNTs/CNFs was fabricated. • Co/Ni@GC/NCNTs/CNFs endows excellent ORR, OER and HER properties. • The as-prepared electrode exhibits high power density of 2100 ± 45 mW cm −2 in MFCs. • Superior property is due to the synergy of abundant active sites and 3D structure.

Mechanochemical coordination self-assembly for Cobalt-based metal-organic framework-derived bifunctional oxygen electrocatalysts

The exploration and preparation of inexpensive, high-performance and stable catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is of significant imperativeness, yet is still on the way. In this study, a facile operation protocol is presented for constructing an exquisite three-dimensional coral reef-like carbon nanotube assembly bridged with N-doped graphene (assigned as 3D CNTAs-NG, which represented carbonization products at 900℃) as highly efficient and durable ORR/OER electrocatalysts. It does not require the introduction of reductive atmosphere. In this tactic, the dicyanamide ligand on the Co-MOF not only was instrumental in the introduction of nitrogen but also acted as the inducer of carbon nanotubes (CNTs) to lock the metallic Co in graphitic carbon layers. Graphene oxide (GO) is chosen as a matrix to pin the CNTs and ensure the uniform distribution of CNTs. The obtained CNTAs-NG structure possesses 3D open porous texture, abundant defects, desired nitrogen bonding type and high specific surface area, providing them with excellent ORR and OER properties. As such, the optimized 3D CNTAs-NG sample shows high onset potential (Eonset = 0.97 V vs. RHE) and half-wave potential (E1/2 = 0.85 V vs. RHE) for ORR and overpotential of 340 mV at 10 mA∙cm−2 for OER. Meanwhile, the prepared optimum catalyst exhibited outstanding durability for ORR and OER in alkaline solutions. This work may pave significant concepts for the synthesis of highly active bifunctional electrocatalysts with intriguing architectures and compositions.

Perovskite La1-xKxCoO3-δ (0 ≤ x ≤ 0.5): a novel bifunctional OER/ORR electrocatalyst and supercapacitive charge storage electrode in a neutral Na2SO4 electrolyte.

The as-prepared La1-xKxCoO3-δ (0 ≤ x ≤ 0.5) showed superior pseudocapacitive charge storage capacity in a neutral 0.5 M Na2SO4 electrolyte and superior electrocatalytic activities for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in a 1 M KOH electrolyte. 30% K doped p-type La0.7K0.3CoO3-δ presents superior OER activity with an overpotential of ∼335 mV at 10 mA cm-2 current rate in a 1 M KOH electrolyte. Additionally, La1-xKxCoO3-δ (0 ≤ x ≤ 0.5) presents an excellent charge-storage capacitance in a neutral 0.5 M Na2SO4 electrolyte resulting in a gravimetric capacitance of the La0.5K0.5CoO3-δ electrode equivalent to 378 F g-1, 282 F g-1, 221 F g-1, 163 F g-1, and 74 F g-1 at a current density of 1 A g-1, 2 A g-1, 3 A g-1, 5 A g-1, and 10 A g-1, respectively. After 2500 continuous cycles of charge/discharge, the La0.5K0.5CoO3-δ//AC cell exhibits higher stability, capacitive retention (94%) and coulombic efficiency (97%). The gravimetric charge storage capacity of ASCs (La0.5K0.5CoO3-δ//AC) in the full cell mode showed capacitance equivalent to 308 F g-1, 287 F g-1, 238 F g-1, 209 F g-1 and 162 F g-1 at current densities of 1 A g-1, 2 A g-1, 3 A g-1, 5 A g-1 and 10 A g-1 in a neutral 0.5 M Na2SO4 electrolyte respectively. Maximum specific power equivalent to ∼6884 W kg-1 was observed at a current density of 10 A g-1 when the specific energy reached ∼57 W h kg-1 for the full cell. The double exchange mechanism coupled with stoichiometric oxygen defects present in the perovskite lattice seems to be operative behind the enhanced electrocatalytic OER properties, and additionally, it improves the charge storage kinetics of the La1-xKxCoO3-δ (0 ≤ x ≤ 0.5) electrode in a neutral Na2SO4 electrolyte for supercapacitor application. This work presents a rational strategy for introducing facile oxygen ion defects into perovskite structured La1-xKxCoO3-δ (0 ≤ x ≤ 0.5) to develop multifunctional electrode materials for a supercapacitor and energy conversion (OER/ORR) electrode of metal-air batteries.

Influence of Chemical Operation on the Electrocatalytic Activity of Ba0.5Sr0.5Co0.8Fe0.2O3−δ for the Oxygen Evolution Reaction

Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) is a promising electrocatalyst for the oxygen evolution reaction (OER) in alkaline solution. The OER activities of BSCF are gradually enhanced by prolonging the duration of electrochemical operation at OER potentials, but the underlying cause is not fully understood. In this study, we investigated the role of chemical operation, equivalent to immersion in alkaline solution, in the time-course of OER enhancement of BSCF. Interestingly, the time-course OER enhancement of BSCF was promoted not only by electrochemical operation, which corresponds to potential cycling in the OER region, but also by chemical operation. In situ Raman measurements clarified that chemical operation had a lower rate of surface amorphization than electrochemical operation. On the other hand, the leaching behavior of A-site cations was comparable between chemical and electrochemical operations. Since the OER activity of BSCF was stabilized by saturating the electrolyte with Ba2+, “chemical” A-site leaching was key to inducing the time-course OER enhancement on perovskite electrocatalysts. Based on these results, we provide a fundamental understanding of the role of chemical operation in the OER properties of perovskites.

Ni-Fe nanoframes via a unique structural formation induced by sonochemical etching.

A uniform nanoframe structure derived from a Prussian blue analogue (PBA) with an internal cavity is successfully synthesized by sonochemical etching. The uniquely structured PBA nanoframes possess a three-dimensional open structure and high surface area, resulting in enhanced electrochemical properties for the oxygen evolution reaction as a model reaction.

Facile synthesis of black phosphorus directly grown on carbon paper as an efficient OER Electrocatalyst: Role of Interfacial charge transfer and induced local charge distribution

Black phosphorus (BP), as a new 2D material, is normally synthesized by a high-pressure and high-temperature (HPHT) method from white and red phosphorus, which severely hinders the further development of BP for any potential applications and leads to search for other potential applications of BP with big challenge. Herein, we develop a facile and efficient Thermal-Vaporization-Transformation (TVT) approach to prepare a highly active BP directly grown on carbon paper as the electrode for Oxygen evolution reaction (OER), showing a low onset potential of 1.45 V versus RHE. Simultaneously, the current density of BP-CP illustrates the excellent electro-catalysis stability only decreases by 3.4% after continuous operation for 10000 s. Meanwhile, the density functional theory (DFT) calculations further illustrates the P-doped carbon layer in the upper side of BP layer is actually responsible for its enhanced OER property, and the adjacent carbon atoms of the embedded P atoms are actually the active sites due to the induced local change distribution by intramolecular change transfer. Considering the facile, but efficient and scalable, TVT approach can directly synthesize BP-CP with excellent OER performance, which is promising for BP electrocatalysts used for OER in metal-air batteries, fuel cells, water-splitting devices, even other key renewable energy.

Oxygen evolution reaction at the Mo/W-doped bismuth vanadate surface: Assessing the dopant role by DFT calculations

The first-principles investigation of M-doped BiVO4-based materials (M = Mo, W) provides a comprehensive understanding of the dopant role in enhancing the photocatalytic properties for Oxygen Evolution Reaction (OER), which is the key-process for water splitting. We found that the beneficial effect of Mo/W doping on bismuth vanadate stems from structural surface re-organizations with the formation of a peculiar site (Biopp), which stabilizes both hydration and catalytic capabilities. Water adsorption is more favourable on Biopp site rather than on top of the dopant Mo/W atoms. Also, the catalytic performances for OER are significantly improved at Biopp site thanks to a stabilization of the crucial intermediate along the OER mechanism. Therefore, the Mo/W dopants exert a non-innocent indirect effect on the catalysis by activating the under-coordinated Biopp site via a long-range pull-back mechanism. These findings pave the route to new design strategies based on doping and defect engineering to push further the development of new photocatalysts for water splitting.

Tremella-like manganese dioxide complex (Fe,Ni)3S4 hybrid catalyst for highly efficient oxygen evolution reaction

Exploring high-efficiency and low-cost electrocatalysts with outstanding durableness for oxygen evolution reaction (OER) is the key to practical production of eco-friendly hydrogen energy by water electrolysis technology, which remains challenging. In this paper, the tremella-like MnO 2 /(Fe,Ni) 3 S 4 hybrid nanostructures are supported on nickel foam matrix by a facile and governable method, with predominant OER properties in 1.0 M KOH solution. Profiting from the synergistic effect between MnO 2 and (Fe,Ni) 3 S 4 , this optimal MnO 2 /(Fe,Ni) 3 S 4 catalyst only requires 220 and 325 mV to fulfill current densities of 10 and 500 mA cm −2 , respectively. Through the inheritance and optimization of MnO 2 and (Fe,Ni) 3 S 4 nanostructures, this hybrid catalyst possesses a large specific surface area, appropriate exposure active site and favorable electrical conductivity. Besides, the self-supported MnO 2 /(Fe,Ni) 3 S 4 electrode exhibits eminent stability at 10 and 100 mA cm −2 during the 20 h OER process. • 1.The tremella-like nanostructure provides plentiful active sites. • 2.Vast openings are beneficial to the conversion of water molecules. • 3.MnO 2 and (Fe,Ni) 3 S 4 form hybrid nanostructures. • 4.This unique hybrid material has a good synergistic effect. • 5.This electrocatalyst exhibits excellent OER activity and stability.

Enhancement of the OER Kinetics of the Less-Explored α-MnO2 via Nickel Doping Approaches in Alkaline Medium.

Development of a low-cost transition metal-based catalyst for water splitting is of prime importance for generating green hydrogen on an industrial scale. Recently, various transition metal-based oxides, hydroxides, sulfides, and other chalcogenide-based materials have been synthesized for developing a suitable anode material for the oxygen evolution reaction (OER). Among the various transition metal-based catalysts, their oxides have received much consideration for OER, especially in lower pH condition, and MnO2 is one of the oxides that have widely been used for the same. The large variation in the structural disorder of MnO2 and internal resistance at the electrode-electrolyte interfaces have limited its large-scale application. By considering the above limitations of MnO2, here in this work, we have designed Ni-doped MnO2 via a simple wet-chemical synthetic route, which has been successfully applied for OER application in 0.1 M KOH solution. Doping of various quantities of Ni into the MnO2 lattices improved the OER properties, and for achieving 10 mA/cm2 current density, the Ni-doped MnO2 containing 0.02 M of Ni2+ ions (coined as MnO2-Ni0.002(M)) demands only 445 mV overpotential, whereas the bare MnO2 required 610 mV overpotential. It has been proposed that the incorporation of nickel ions into the MnO2 lattices leads to an electron transfer from the Ni3+ ions to Mn4+, which in turn facilitates the Jahn-Teller distortion in the Mn-O octahedral unit. This electron transfer and the creation of a structural disorder in the Mn sites result in the improvization of the OER properties of the MnO2 materials.