Low-cost Oxygen Evolution Reaction Research Articles

Fe-Ni-based alloys as highly active and low-cost oxygen evolution reaction catalyst in alkaline media.

NiFe-based oxo-hydroxides are highly active for the oxygen evolution reaction but require complex synthesis and are poorly durable when deposited on foreign supports. Herein we demonstrate that easily processable, Earth-abundant and cheap Fe-Ni alloys spontaneously develop a highly active NiFe oxo-hydroxide surface, exsolved upon electrochemical activation. While the manufacturing process and the initial surface state of the alloys do not impact the oxygen evolution reaction performance, the growth/composition of the NiFe oxo-hydroxide surface layer depends on the alloying elements and initial atomic Fe/Ni ratio, hence driving oxygen evolution reaction activity. Whatever the initial Fe/Ni ratio of the Fe-Ni alloy (varying between 0.004 and 7.4), the best oxygen evolution reaction performance (beyond that of commercial IrO2) and durability was obtained for a surface Fe/Ni ratio between 0.2 and 0.4 and includes numerous active sites (high NiIII/NiII capacitive response) and high efficiency (high Fe/Ni ratio). This knowledge paves the way to active and durable Fe-Ni alloy oxygen-evolving electrodes for alkaline water electrolysers.

Recent progress in hierarchical nanostructures for Ni-based industrial-level OER catalysts.

Exploring efficient and low-cost oxygen evolution reaction (OER) electrocatalysts reaching the industrial level current density is crucial for hydrogen production via water electrolysis. In this feature article, we summarize the recent progress in hierarchical nanostructures for the industrial-level OER. The contents mainly concern (i) the design of a hierarchical structure; (ii) a Ni-based hierarchical structure for the industrial current density OER; and (iii) the surface reconstruction of the hierarchical structure during the OER process. The work provides valuable guidance and insights for the manufacture of hierarchical nanomaterials and devices for industrial applications.

Bifunctional Square-Planar NiO4 Coordination of Topotactic LaNiO2.0 Films for Efficient Oxygen Evolution Reaction.

The high-efficient and low-cost oxygen evolution reaction (OER) is decisive for applications of oxide catalysts in metal-air batteries, electrolytic cells, and energy-storage technologies. Delicate regulations of active surface and catalytic reaction pathway of oxide materials principally determine thermodynamic energy barrier and kinetic rate during catalytic reactions, and thus have crucial impacts on OER performance. Herein, a synergistic modulation of catalytically active surface and reaction pathway through facile topotactic transformations switching from perovskite (PV) LaNiO3.0 film to infinite-layer (IL) LaNiO2.0 film is demonstrated, which absolutely contributes to improving OER performance. The square-planar NiO4 coordination of IL-LaNiO2.0 brings about more electrochemically active metal (Ni+ ) sites on the film surface. Meanwhile, the oxygen-deficient driven PV- IL topotactic transformations lead to a reaction pathway converted from absorbate evolution mechanism to lattice-oxygen-mediated mechanism (LOM). The non-concerted proton-electron transfer of LOM pathway, evidenced by the pH-dependent OER kinetics, further boosts the OER activity of IL-LaNiO2.0 films. These findings will advance the in-depth understanding of catalytic mechanisms and open new possibilities for developing highly active perovskite-derived oxide catalysts.

Hierarchical Heterogeneous NiFe Layered Double Hydroxides for Efficient Solar-Powered Water Oxidation.

Highly active, stable, and low-cost oxygen evolution reaction (OER) electrocatalysts are urgently needed for the realization of large-scale industrial hydrogen production via water electrolysis. Layered double hydroxides (LDHs) stand out as one of the most promising nonprecious electrocatalysts worth pursuing. Here, a hierarchical heterogeneous Ni2+Fe3+@Ni2+Fe2+ LDH was successfully synthesized via a sequential electrodeposition technique using separate electrolytes containing iron precursors with different valence states (Fe2+, Fe3+). The underlying highly crystalline Ni2+Fe2+ LDH nanosheet array provides a large surface for the catalytically more active Ni2+Fe3+ LDH overlayer with low crystallinity. The resulting Ni2+Fe3+@Ni2+Fe2+ LDH demonstrates excellent OER activity with overpotentials of 218 and 265 mV to reach current densities of 10 and 100 mA cm-2, respectively, as well as good long-term stability for 30 h even at a high current density of 500 mA cm-2. In an overall water splitting, an electrolyzer using an electrocatalyst of Sn4P3/CoP2 as a cathode requires only a cell voltage of 1.55 V at 10 mA cm-2. Furthermore, the solar-powered overall water splitting system consisting of our electrolyzer and a perovskite/Si tandem solar cell exhibits a high solar-to-hydrogen conversion efficiency of 15.3%.

Design of high-entropy antiperovskite metal nitrides as highly efficient electrocatalysts for oxygen evolution reaction

Rational design of effective, stable and low-cost oxygen evolution reaction (OER) catalysts is vital for the overall efficiency of water splitting. As a novelty branch of transition metal nitrides, antiperovskite nitrides have been considered as potential alternative OER electrocatalysts due to their high flexibility in elemental composition and excellent conductivity. Particularly, high-entropy antiperovskite nitride materials with multiple elements occupying the equivalent lattice sites are considered as potentially effective application in field of catalysis. Here, we first report the OER results about Ni-based high-entropy antiperovskite nitrides. The Cu0.5Fe0.5NNi2Co0.5Fe0.5 as the high-entropy antiperovskite nitride is designed for an OER catalyst with promising electrocatalytical OER performance in alkaline medium (low overpotential 370 mV at 10 mA cm−2, low overpotential 627 mV at high current density of 400 mA cm−2 (almost the same overpotential with commercial RuO2), small Tafel slope 55 mV dec−1 and long-term stability). The results provide a novel OER catalyst based on high-entropy antiperovskite metal nitrides and will push forward the strategic guidelines for design of highly efficient catalysts.

Nickel-Cobalt-Iron Ternary Layered Double Hydroxide Nanoarrays for Superior Performance of Electrocatalytic Water Splitting

The design of high-performance and low-cost oxygen evolution reaction (OER) electrocatalysts is crucial for environment friendly hydrogen production. Some transition metals have been proven to be good substitutes for noble metals due to their unique electronic structural characteristics and good electrocatalytic performances, with examples including nickel and cobalt, which are usually used to prepare OER electrocatalysts. In this work, we synthesized three-dimensional Ni-Co-Fe ternary layered double hydroxide nanosheet array electrocatalysts via hydrothermal process. Iron element was introduced into the Ni-Co based hydroxide. The ternary layered double hydroxide has a nanoarrays microstructure. Theoretical analysis confirms that by adjusting the ratio of Ni/Co/Fe, the microstructure of the catalyst changes significantly. Attributed to the special nanostructure, the catalysts show superior catalytic activities in oxygen evolution reaction (OER). The results show that a small overpotential of 222 mV at the current density of 20 mA·cm−2 for the OER in 1.0 M KOH is acquired. A small Tafel slope of 61.22 mVdec−1 and a maximum specific capacitance of 239 Fg−1 are also obtained.

Catalyst-Support Interactions Promoted Acidic Electrochemical Oxygen Evolution Catalysis: A Mini Review.

In the context of the growing human demand for green secondary energy sources, proton-exchange membrane water electrolysis (PEMWE) is necessary to meet the high-efficiency production of high-purity hydrogen required for proton-exchange membrane fuel cells (PEMFCs). The development of stable, efficient, and low-cost oxygen evolution reaction (OER) catalysts is key to promoting the large-scale application of hydrogen production by PEMWE. At present, precious metals remain irreplaceable in acidic OER catalysis, and loading the support body with precious metal components is undoubtedly an effective strategy to reduce costs. In this review, we will discuss the unique role of common catalyst-support interactions such as Metal-Support Interactions (MSIs), Strong Metal-Support Interactions (SMSIs), Strong Oxide-Support Interactions (SOSIs), and Electron-Metal-Support Interactions (EMSIs) in modulating catalyst structure and performance, thereby promoting the development of high-performance, high-stability, low-cost noble metal-based acidic OER catalysts.

Ar plasma assists in enhanced oxygen evolution kinetics of MOG-derived multicomponent transition metal sulfides.

Transition metal sulfides are low-cost oxygen evolution reaction (OER) electrocatalysts that can potentially substitute noble metal catalysts. However, the adsorption process of their OER is impeded by their intrinsic poor catalytic activity. Constructing heterojunction and vacancy defects in transition metal sulfides is an efficient method to promote the process of oxygen evolution. Herein, a facile approach based on in situ sulfurization of metal-organic gels (MOGs) and a short-time plasma treatment was developed to fabricate vacancy-modified polymetallic sulfides heterojunction. The synergistic effect of the multi-component heterojunction and sulfur vacancy contributed greatly to improving the electron migration efficiency and OER ability of the electrocatalyst. As a result, the optimum oxygen evolution activity was achieved with appropriate surface vacancy concentrations by regulating the plasma radio frequency powers. The plasma-treated catalyst under 400 W showed the best OER performance (lower overpotential of 235 mV in 1 M KOH solution with the Tafel slope of 31 mV dec-1) and good durability over 11 h of chronopotentiometry testing. This work sheds new light on constructing multimetal-based heterojunction electrocatalysts with rich vacancy defects for oxygen evolution reactions.

Facile synthesis of Co-Ni layered double hydroxides nanosheets wrapped on a prism-like metal-organic framework for efficient oxygen evolution reaction

The construction of low-cost oxygen evolution reaction (OER) electrocatalysts with high activity and good durability is a considerable challenge for facilitating the efficient utilization of green energy. Herein, the prism-like materials of institute lavoisier frameworks-88 (MIL-88) was first synthesized by a hydrothermal method. Then, Co-Ni layered double hydroxides (CoNi-LDHs) nanosheets were directly wrapped on the MIL-88 surface by electrodeposition to form core-shell MIL-88@CoNi-LDHs composites. Due to the distinct structure and synergistic effect between the MIL-88 core and CoNi-LDHs shell, it was found that MIL-88@CoNi-LDHs had outstanding OER activity with a small Tafel slope (45.55 mV dec-1), low overpotential (314 mV) at 10 mA cm−2, and superior durability. This study provides a prospective pathway to exploit highly efficient low-cost electrocatalysts for OER.

Topologic transition-induced abundant undercoordinated Fe active sites in NiFeOOH for superior oxygen evolution

Highly active, robust and low-cost oxygen evolution reaction (OER) electrodes are urgently required to satisfy the industrial hydrogen production via water electrolysis. However, numerous earth-abundant materials have severely suffered from the low stability over thousands of hours at large current densities. Herein, ultrathin NiFeOOH nanosheets with abundant undercoordinated Fe active sites on a Ni foam electrode for OER were obtained via an electrochemically topologic transition process. They deliver a low overpotentials of 210 mV at 10 mA cm-2 and a small Tafel slope of 32 mV dec-1 owing to the abundant Fe active sites and exhibit high stability at high current densities of 400–600 mA cm-2 over 2000 h due to their strong adhesion to Ni foam. Moreover, only a 370 mV overpotentials is required to produce a high current density of 400 mA cm-2 in a two-electrode water electrolysis system, demonstrating an energy efficiency as high as ∼77%.

Amorphous CoFeB nanosheets with plasmon-regulated dynamic active sites for electrocatalytic water oxidation

Exploring efficient and low-cost oxygen evolution reaction (OER) electrocatalysts is of crucial importance. Here, we report a surface plasmon resonance (SPR) engineering strategy to regulate surface reconstruction of CoFeB nanosheets by decorating plasmonic MoO2 nanospheres (MoO2/CoFeB), in which the SPR effect of MoO2 offers an additional acceleration for the conversion of inactive Co species to active cobalt oxyhydroxide on the CoFeB surface under visible light. Our results also indicate the real reactive surface for CoFeB is in the form of CoFeOOH with adsorbed BO2− that has positive effect. The MoO2/CoFeB shows superior OER performance with a low overpotential (209 mV at J=10 mA cm−2). However, such an accelerated reconstruction behavior would be self-terminated once the anodic voltage increases to thoroughly oxidize the MoO2 to high valence state (+6). This work inspires us to develop a rational strategy to improve the catalytic performance by properly regulating the surface reconstruction.

Electrochemical hydroxidation of sulfide for preparing sulfur-doped NiFe (oxy) hydroxide towards efficient oxygen evolution reaction

The well-known NiFe hydroxides show tremendous promise as low-cost oxygen evolution reaction (OER) catalysts, which however suffer from the rapid decline of activity at current densities exceeding 100 mAcm−2. Herein, we constructed a sulfur-doped OER electrode ((Ni7Fe3)OOH-S) by facile sulfurization and anodic displacement processes. The as-prepared (Ni7Fe3)OOH-S electrode shows an overpotential of 238 mV at 10 mA cm−2 in 1 M KOH at 25 °C, which is due to the high intrinsic catalytic activity, the super hydrophilic nature of the electrode for the S dopant. DFT calculations reveal that the S dopant changes the electronic structure and charge density (NiFe)OOH, thereby optimizing the OER rate-determining step, improving the binding energy for OER intermediates, which ensures the high intrinsic catalytic activity. In addition, the long-term stability (e.g., 200 h) at industrial-level current density (399 mV at 500 mA cm−2) holds the promise for the real application of the (Ni7Fe3)OOH-S electrode. Furthermore, a solar-powered electrolyzer consisting of the (Ni7Fe3)OOH-S anode and a 20 % Pt/C@CC cathode operates successfully at a low voltage of 1.46 V(10 mA cm−2) in 10 M KOH at 75 °C. Overall, the combined sulfidation and anodic displacement approach could be a general approach to prepare efficient and durable catalysts for water electrolyzers.

Tailoring B-site of lead-ruthenate pyrochlore for boosting acidic water oxidation activity and stability

Achieving highly active, stable and low cost oxygen evolution reaction (OER) catalysts is a significant challenge for promoting splitting water technology in acidic media. Herein, we report a low-temperature pyrolysis cation exchange resin (CER) strategy to synthesize lead-ruthenate pyrochlore (Pb2[Ru2−xPbx]O7-δ) catalyst with different contents of Pb substituted at B-site. We demonstrated temperature effectively influence the amount of Pb at B-site, further modulated the electronic states of Ru and the concentration of oxygen defects. Benefiting from rich oxygen defects, the representative PRPO-350 catalyst exhibits outstanding OER activity with a overpotential of 174 mV at 10 mA cm−2geo, a super-low Tafel slope of 28.8 mV dec-1 and excellent stability up to 150 h in acid water. DFT calculations have demonstrated that the such structure will lead to the O-2p orbital closing to the Fermi level, eventually boosts the OER activity.

Accelerating water oxidation kinetics via synergistic in-layer modification and interlayer reconstruction over hetero-epitaxial Fe-Mn-O nanosheets

Developing high-performance and low-cost oxygen evolution reaction (OER) electrocatalysts is critical for implementing industrial H2 production. Herein, ultrathin Fe-Mn-O hetero-nanosheets consisting of crystalline ε-Fe2O3 intercalated in amorphous Fe-doped δ-MnO2 have been fabricated through facile alkali hydrolysis of FeMn-based coordination polymer. Abundant Mn3+ active sites and oxygen vacancies are generated in Fe-doped δ-MnO2 layer due to in-layer/interlayer reformations, where interstitial ε-Fe2O3 is engineered to reinforce stability and conductivity. The optimal 0.5Fe-Mn-O nanosheets exhibit superb activity with low overpotentials of 258 (322) mV at 10 (300) mA cm−2 for OER together with strong stability under large current density over 100 h, ranking it among the best MnO2-based electrocatalysts. Importantly, in situ interlayer reconstruction from ε-Fe2O3 to β-FeOOH during OER has been unveiled, the evolved β-FeOOH triggers strong interfacial electronic coupling, which synergizes with oxygen vacancies and Fe3+ dopants to modulate surface electronic structure of δ-MnO2 for intermediates adsorption.

Engineering of P vacancies and phosphate on Fe-doped Ni2P nanosheet arrays for enhanced oxygen evolution

High-efficient and low-cost oxygen evolution reaction (OER) electrocatalysts are of considerable significance for large-scale electrocatalytic water splitting to produce hydrogen. In this work, we have introduced O2 plasma to engineer Fe-doped Ni2P (Fe-Ni2P) nanosheets, which is grown on the conductive NiFe foam. Interestingly, this facile and rapid plasma treatment can simultaneously achieve defect engineering (P vacancies) and the formation of new species (phosphate). The P vacancies could modulate the electronic structure of the electrocatalyst for the OER process, while the formed phosphate species could facilitate water adsorption and improve the charge transfer. Consequently, the O2-plasma treated Fe-Ni2P nanosheets with rough surface and nanoholes exhibit low overpotentials of 207 and 218 mV at 50 and 100 mA cm−2, small Tafel slope of 45 mV dec−1 and excellent durability in alkaline electrolyte. Our work reveals the delicate structural transformation of the plasma-engineered material, and provides insights of the structure-property relationship of high-performance OER electrocatalyst.

Interface engineering of NixSy@MoS2 heterostructured nanorods as high-efficient electrocatalysts for water splitting

Robust and low-cost oxygen evolution reaction (OER) electrocatalysts at low overpotentials play an increasingly pivotal role in clean energy storage and conversion systems. The emerging catalyst with core-shell heterostructure has excited the potentiality of non-noble-metal candidates. Herein, in order to enhance the sufficient exposure and utilization of actives sites and accelerate the electron transfer rate of catalyst, NixSy@MoS2 core-shell nanorods decorated NiSe2 framework (NixSy@MoS2/NiSe2) electrocatalyst has been successfully prepared via interface engineering. As expected, the as-prepared catalyst shows an outstanding OER activity with a small overpotential of 360 mV to drive 100 mA cm−2 and a Tafel slope of 64 mV dec−1. More importantly, a low cell voltage of 1.40 V is achieved for the NixSy@MoS2/NiSe2 based water splitting electrolyzer at 10 mA cm−2, and it shows negligible decrement after continuous operation for 100 h. Furthermore, density functional theory (DFT) calculations further uncovered the synergetic catalytic effect between the NixSy@MoS2 core-shell nanorods and the NiSe2 framework played a key role in generating more charge carriers and declining the energy barriers in the process of forming intermediates.

A Novel Phosphide Derived From Metal-Organic Frameworks as Cost-Effective Electrocatalyst for Oxygen Evolution Reaction

Abstract Developing an efficient, green, and low-cost non noble metal catalyst toward oxygen evolution reaction (OER) has been urgent for new generation of sustainable energy technologies. Herein, the Co/Ni metal-organic frameworks (MOFs) derived metal phosphides/carbon matrix composites are successfully produced by the precipitation-carbonization-phosphorization processes. The obtained samples are characterized and analyzed for structural and morphological investigation. Electrochemical tests for OER are performed in the alkaline medium. The positive effects of P, Ni doping in MOFs on the structure and properties of composites have been analyzed. Benefitting from the unique structure of three-dimensional flower-like polyhedron with rich structure and higher porosity, the NiCo-P/NC catalyst exhibits the lowest overpotential of 0.32 V compared with the commercial IrO2 (0.34 V) at 10 mA/cm2, as well as outstanding stability and kinetic mechanism. Besides, the cost of the proposed novel material is calculated to be 4.337 US$/g, which is only 1.57% of that of commercial IrO2 (276 US$/g). The results obtained from the MOF-derived low-cost and high-efficiency OER catalyst would provide a new perspective on application of electrochemical storage and batteries.

Electronic structure modulation with ultrafine Fe3O4 nanoparticles on 2D Ni-based metal-organic framework layers for enhanced oxygen evolution reaction

Two-dimensional (2D) metal organic frameworks (MOFs) are emerging as low-cost oxygen evolution reaction (OER) electrocatalysts, however, suffering aggregation and poor operation stability. Herein, ultrafine Fe3O4 nanoparticles (diameter: 6 ± 2 nm) are homogeneously immobilized on 2D Ni based MOFs (Ni-BDC, thickness: 5 ± 1 nm) to improve the OER stability. Electronic structure modulation for enhanced catalytic activity is studied via adjusting the amount of Fe3O4 nanoparticles on Ni-BDC. The optimal Fe3O4/Ni-BDC achieves the best OER performance with an overpotential of 295 mV at 10 mA cm−2, a Tafel slope of 47.8 mV dec-1 and a considerable catalytic durability of more than 40 h (less than 5 h for Ni-BDC alone). DFT calculations confirm that the active sites for Fe3O4/Ni-BDC are mainly contributed by Fe species with a higher oxidation state, and the potential-determining step (PDS) is the formation of the adsorbed O* species, which are facilitated in the composite.

FeMn bimetallic MOF directly applicable as an efficient electrocatalyst for overall water splitting

The preparation of high-efficiency, stable and low-cost oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) electrocatalysts is always a challenge for new energy systems. In this work, a simple hydrothermal synthesis method was used to obtain FeMn bimetallic organic materials (FeMn-MOF/NF) grown on foamed nickel (NF) in one step. Moreover, FeMn-MOF/NF(1:1) had larger electrochemical specific surface area and unique nano-flower-like structure. The overpotentials of OER and HER in alkaline solution at a current density of 50 mA·cm−2 were 290 mV and 260 mV, respectively, and the total water splitting potential at this current density is only 1.7 V. The excellent activity and stability were attributed to the synergistic effect of FeMn. The bimetal and abundant active sites could promote the release of oxygen during the catalytic process.

Electrochemical synthesis of amorphous metal hydroxide microarrays with rich defects from MOFs for efficient electrocatalytic water oxidation

MOFs featuring adjustable functions show good prospects for creating low-cost oxygen evolution reaction (OER) electrocatalysts, but their poor stability and conductivity seriously limit their real applications. Herein, we report a general in-situ electrochemical approach for the synthesis of amorphous metal hydroxide-based microarrays assembled on nickel foam (NF) by using leaflike CoM-ZIF-L as precursors for boosting OER performance. It is demonstrated that an electrochemical cyclic voltammetry (CV) redox process can promote the ligand substitution of CoM-ZIF-L to afford highly-active amorphous metal hydroxides with abundant oxygen defects via activating the reversible redox of metal ions, removing 2-methylimidazole and subsequently capping OH−. As expected, the optimized aCo(OH)2-ZIF-L/NF can provide rich catalytic sites, good conductivity and short ion diffusion paths, all of which are responsible for its excellent OER activity. Further experiment and DFT calculation results confirm that the in-situ formed defective amorphous metal oxy(hydroxide) is the real active species for this electrocatalytic reaction.