Oxygen Evolution Reaction Catalytic Performance Research Articles

Tuning Surface Electronic Configuration of NiFe LDHs Nanosheets by Introducing Cation Vacancies (Fe or Ni) as Highly Efficient Electrocatalysts for Oxygen Evolution Reaction.

Intrinsically inferior electrocatalytic activity of NiFe layered double hydroxides (LDHs) nanosheets is considered as a limiting factor to inhibit the electrocatalytic properties for oxygen evolution reaction (OER). Proper defect engineering to tune the surface electronic configuration of electrocatalysts may significantly improve the intrinsic activity. In this work, the selective formation of cation vacancies in NiFe LDHs nanosheets is successfully realized. The as-synthesized NiFe LDHs-VFe and NiFe LDHs-VNi electrocatalysts show excellent activity for OER, mainly attributed to the introduction of rich iron or nickel vacancies in NiFe LDHs nanosheets, which efficiently tune the surface electronic structure increasing the adsorbing capacity of OER intermediates. Density functional theory (DFT) computational results also further indicate that the OER catalytic performance of NiFe LDHs can be pronouncedly improved by introducing Fe or Ni vacancies.

Atomic Iridium Incorporated in Cobalt Hydroxide for Efficient Oxygen Evolution Catalysis in Neutral Electrolyte.

Developing highly efficient catalysts for oxygen evolution reaction (OER) in neutral media is extremely crucial for microbial electrolysis cells and electrochemical CO2 reduction. Herein, a facile one-step approach is developed to synthesize a new type of well-dispersed iridium (Ir) incorporated cobalt-based hydroxide nanosheets (nominated as CoIr) for OER. The Ir species as clusters and single atoms are incorporated into the defect-rich hydroxide nanosheets through the formation of rich Co-Ir species, as revealed by systematic synchrotron radiation based X-ray spectroscopic characterizations combining with high-angle annular dark-field scanning transmission electron microscopy measurement. The optimized CoIr with 9.7 wt% Ir content displays highly efficient OER catalytic performance with an overpotential of 373 mV to achieve the current density of 10 mA cm-2 in 1.0 m phosphate buffer solution, significantly outperforming the commercial IrO2 catalysts. Further characterizations toward the catalyst after undergoing OER process indicate that unique Co oxyhydroxide and high valence Ir species with low-coordination structure are formed due to the high oxidation potentials, which authentically contributes to superior OER performance. This work not only provides a state-of-the-art OER catalyst in neutral media but also unravels the root of the excellent performance based on efficient structural identifications.

Self-Assembly of Ni–Fe Layered Double Hydroxide on Fe Foam as 3D Integrated Electrocatalysts for Oxygen Evolution: Dependence of the Catalytic Performance on Anions under in Situ Condition

Herein, we demonstrate a very facile self-assembly method to fabricate a Ni–Fe layered double hydroxide (LDH) 3D integrated film at ambient temperature without energy input as a highly efficient electrocatalyst for oxygen evolution reaction (OER). By this method, we can readily regulate the Ni–Fe proportion and change the embedded guest anions into the LDH under our in situ synthetic condition by just using different nickel salts to prepare Ni–Fe LDH. It is found that the Ni–Fe ratio and the embedded guest anions can dramatically influence the corresponding OER catalytic performance. An excellent OER activity that delivering overpotentials of about 210 and 240 mV to reach 10 and 100 mA cm–2 current densities in 1.0 M KOH was achieved.

Copper oxide nanosheets prepared by molten salt method for efficient electrocatalytic oxygen evolution reaction with low catalyst loading

In this present study, we report tuning the catalytic activity in heterogeneous copper oxide (CuO) material as an efficient catalyst in 1.0 M KOH for the oxygen evolution reaction (OER) with low catalyst loading. The CuO materials were facilely synthesized by a simple molten salt method at a high temperature and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) surface area analysis. The catalytic water oxidation activity is affected by many factors, such as the catalyst morphologies, electronic double-layer capacitance, and the conductivity. Under optimal conditions, the CuO material prepared at 900 °C showed the nanosheets structure with more exposed catalytic active sites and demonstrated high catalytic performance for OER with a low overpotential of only 420 mV to achieve 10 mA/cm2 and 520 mV to achieve 40 mA/cm2, respectively. Furthermore, when CuO nanosheets are mixed with multi-walled carbon nanotubes (MWCNTs), the catalyst loading can be greatly decreased from 0.7 mg/cm2 to 0.14 mg/cm2 and the overpotential for 40 mA/cm2 is also lowered to 470 mV.

NiCo Alloy Nanoparticles Decorated on N‐Doped Carbon Nanofibers as Highly Active and Durable Oxygen Electrocatalyst

AbstractThe exploring of catalysts with high‐efficiency and low‐cost for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is one of the key issues for many renewable energy systems including fuel cells, metal–air batteries, and water splitting. Despite several decades pursuing, bifunctional oxygen catalysts with high catalytic performance at low‐cost, especially the one that could be easily scaled up for mass production are still missing and highly desired. Herein, a hybrid catalyst with NiCo alloy nanoparticles decorated on N‐doped carbon nanofibers is synthesized by a facile electrospinning method and postcalcination treatment. The hybrid catalyst NiCo@N‐C 2 exhibits outstanding ORR and OER catalytic performances, which is even surprisingly superior to the commercial Pt/C and RuO2 catalysts, respectively. The synergetic effects between alloy nanoparticles and the N‐doped carbon fiber are considered as the main contributions for the excellent catalytic activities, which include decreasing the intrinsic and charge transfer resistances, increasing CC, graphitic‐N/pyridinic‐N contents in the hybrid catalyst. This work opens up a new way to fabricate high‐efficient, low‐cost oxygen catalysts with high production.

Ultrafine and highly disordered Ni2Fe1 nanofoams enabled highly efficient oxygen evolution reaction in alkaline electrolyte

Nickel iron hydroxides are the most promising non-noble electrocatalysts for oxygen evolution reaction (OER) in alkaline media. By in situ reduction of metal precursors, compositionally controlled three-dimensional NixFey nanofoams (NFs) are synthesized with high surface area and uniformly distributed bimetallic networks. The resultant ultrafine and highly disordered amorphous Ni2Fe1 NFs exhibit extraordinary electrocatalytic performance toward OER and overall water splitting in alkaline media. At a potential as low as 1.42V (vs. RHE), Ni2Fe1 NFs can deliver a current density of 10mA/cm2 and show negligible activity loss after 12h stability test. Even at large current flux of 100mA/cm2, an ultralow overpotential of 0.27V is achieved, which is about 0.18V more negative than benchmark RuO2. Both ex-situ Mӧssbauer spectroscopy and X-ray Absorption Spectroscopy reveal a phase separation and transformation for the Ni2Fe1 catalyst during OER process. The evolution of oxidation state and disordered structure of Ni2Fe1 might be a key to the high catalytic performance for OER.

Synthesis of Ni–Ir Nanocages with Improved Electrocatalytic Performance for the Oxygen Evolution Reaction

Design and fabrication of inexpensive and efficient oxygen evolution reaction (OER) catalysts are of great importance for polymer electrolyte membrane water electrolyzers (PEMWEs). Although the best electrocatalyst is IrO2 for OER in the PEMWEs, the practical application of Ir has been impeded because of its high cost and limited activity. Herein, a galvanic replacement reaction mechanism was developed for the preparation of polycrystalline Ni–Ir nanocages (NCs) by using Ni nanoparticles as templates. The formation of Ni–Ir NCs achieves the enhancement of OER catalytic performance, accompanied by the reduction of Ir loading but significantly increasing the efficiency of Ir atoms. The as-prepared Ni2.53Ir NCs exhibit improved catalytic activity toward OER in acid solution, which requires only an overpotential of 302 mV to deliver a current density of 10 mA/cm2. At an overpotential of 300 mV, the Ir-based mass activity of Ni2.53Ir catalysts reaches 114.7 mA/mgIr, which is 2.1 times higher than that of comme...

Iron-Cobalt Phosphomolybdate with High Electrocatalytic Activity for Oxygen Evolution Reaction.

Iron-cobalt phosphomolybdate (FeCoPM12 ) nanoparticles, which are highly efficient catalytic materials for the oxygen evolution reaction (OER), were fabricated through a coprecipitation route. Compared with iron-cobalt hydroxide and state-of-the-art RuO2 electrocatalysts, the as-prepared FeCoPM12 sample exhibited robust OER catalytic activity with a low overpotential of 258 mV at a current density of 10 mA cm-2 and a small Tafel slope of 33 mV dec-1 . Moreover, the as-synthesized sample presented preferable stability and after 10 h at 1.52 V the current density degraded by merely 8.3 %. This is ascribed to the high electrochemical stability and small porous structure of FeCoPM12 , which provide effective electron transmission and improve the catalytic performance for OER in alkaline media.

Dual–phase Spinel MnCo2O4 Nanocrystals with Nitrogen-doped Reduced Graphene Oxide as Potential Catalyst for Hybrid Na–Air Batteries

The electrochemical performance of Na–air batteries have a significant dependence on the type of electrocatalyst used for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, a dual-phase spinel MnCo2O4 with nitrogen-doped reduced graphene oxide hybrid (dp-MnCo2O4/N-rGO) employed in a hybrid Na-air battery system was demonstrated simultaneous electrocatalytic characteristic toward both ORR and OER, which showed comparable ORR and superior OER catalytic performance over commercial Pt/C. The fabricated dual-phase cobalt manganese spinel nanoparticles, the introduced dopants (nitrogen atoms), and the electrical and chemical coupling between the oxide nanoparticles and nanocarbon backbones significantly contribute to the high catalytic performance of dp-MnCo2O4/N-rGO. The proposed catalyst exhibited a slightly higher discharge voltage of 2.75V and lower charge voltage of 3.14V compared to that of a commercial Pt/C (2.73 and 3.35V, respectively). The hybrid battery showed a low overpotential of 0.39V and improved round-trip energy efficiency. The battery exhibited excellent discharge stability and no significant degradation was observed during the 25 cycles due to the moderate particle size of dp-MnCo2O4 and large active N-doped surface area. Therefore, dp-MnCo2O4/N-rGO could be a promising bifunctional catalyst for enhancing the electrochemical performance of hybrid Na-air batteries.

Regulating Water-Reduction Kinetics in Cobalt Phosphide for Enhancing HER Catalytic Activity in Alkaline Solution.

Electrochemical water splitting to produce hydrogen renders a promising pathway for renewable energy storage. Considering limited electrocatalysts have good oxygen-evolution reaction (OER) catalytic activity in acid solution while numerous economical materials show excellent OER catalytic performance in alkaline solution, developing new strategies that enhance the alkaline hydrogen-evolution reaction (HER) catalytic activity of cost-effective catalysts is highly desirable for achieving highly efficient overall water splitting. Herein, it is demonstrated that synergistic regulation of water dissociation and optimization of hydrogen adsorption free energy on electrocatalysts can significantly promote alkaline HER catalysis. Using oxygen-incorporated Co2 P as an example, the synergistic effect brings about 15-fold enhancement of alkaline HER activity. Theory calculations confirm that the water dissociation free energy of Co2 P decreases significantly after oxygen incorporation, and the hydrogen adsorption free energy can also be optimized simultaneously. The finding suggests the powerful effectiveness of synergetic regulation of water dissociation and optimization of hydrogen adsorption free energy on electrocatalysts for alkaline HER catalysis.

Effective Construction of High-quality Iron Oxy-hydroxides and Co-doped Iron Oxy-hydroxides Nanostructures: Towards the Promising Oxygen Evolution Reaction Application

Rational design of high efficient and low cost electrocatalysts for oxygen evolution reaction (OER) plays an important role in water splitting. Herein, a general gelatin-assisted wet chemistry method is employed to fabricate well-defined iron oxy-hydroxides and transitional metal doped iron oxy-hydroxides nanomaterials, which show good catalytic performances for OER. Specifically, the Co-doped iron oxy-hydroxides (Co0.54Fe0.46OOH) show the excellent electrocatalytic performance for OER with an onset potential of 1.52 V, tafel slope of 47 mV/dec and outstanding stability. The ultrahigh oxygen evolution activity and strong durability, with superior performance in comparison to the pure iron oxy-hydroxide (FeOOH) catalysts, originate from the branch structure of Co0.54Fe0.46OOH on its surface so as to provide many active edge sites, enhanced mass/charge transport capability, easy release oxygen gas bubbles, and strong structural stability, which are advantageous for OER. Meanwhile, Co-doping in FeOOH nanostructures constitutes a desirable four-electron pathway for reversible oxygen evolution and reduction, which is potentially useful for rechargeable metal−air batteries, regenerative fuel cells, and other important clean energy devices. This work may provide a new insight into constructing the promising water oxidation catalysts for practical clean energy application.

Graphene-like holey Co3O4 nanosheets as a highly efficient catalyst for oxygen evolution reaction

Co3O4 nanosheets with a graphene-like holey structure are successfully synthesized through a bottom-up self-assembly approach and utilized as a catalyst for the oxygen evolution reaction (OER). This unique nanostructure possesses a large fraction of low-coordinated surface atoms and highly accessible surface areas due to its atomic thickness and mesoporosity, which could provide abundant active sites and facilitate the electrode/electrolyte contact for OER catalysis. In addition, density functional theory (DFT) calculations reveal that the loss of the neighboring layers gives the ultrathin nanostructure remarkable lattice distortion, which leads to decreased energy barriers for facile mass conversion and transfer on the surface of the catalyst. As a result, the graphene-like holey Co3O4 nanosheets exhibit excellent OER catalytic performance with low onset potential of 0.617 V vs. Hg/HgO, high current density of 12.26 mA cm-2 at 0.8 V vs. Hg/HgO, and long-term stability with negligible fading in current density after 2000 cycles, significantly outperforming the performances of conventional Co3O4 nanostructures and commercial IrO2. This unique graphene-like holey structure should be of great benefit for applications ranging from electronic devices to energy conversion and storage systems.

Beyond the top of the volcano? – A unified approach to electrocatalytic oxygen reduction and oxygen evolution

We study the oxygen reduction (ORR) and the oxygen evolution reaction (OER) and based on previous obtained mechanistic insight we provide a unified general analysis of the two reactions simultaneously. The analysis shows that control over at least two independent binding energies is required to obtain a reversible perfect catalyst for both ORR and OER. Often only the reactivity of the surface is changed by changing from one material to another and all binding energies scale with the reactivity. We investigate the limitation in efficiency imposed by these linear scaling relations. This analysis gives rise to a double volcano for ORR and OER, with a region in between, forbidden by the scaling relations. The reversible perfect catalyst for both ORR and OER would fall into this “forbidden region”. Previously, we have found that hydrogen acceptor functionality on oxide surfaces can improve the catalytic performance for OER beyond the limitations originating from the scaling relations. We use this concept to search for promising combinations of binding sites and hydrogen donor/acceptor sites available in transition metal doped graphene, which can act as a catalyst for ORR and OER. We find that MnN4-site embedded in graphene by itself or combined with a COOH is a promising combination for a great combined ORR/OER catalyst.

Sub-1 nm Nickel Molybdate Nanowires as Building Blocks of Flexible Paper and Electrochemical Catalyst for Water Oxidation.

Sub-1 nm, extremely long nickel molybdate nanowires are synthesized based on a good/poor solvent system. The ultrathin nanowires can be hierarchically assembled into flexible, free-standing films with good mechanical properties. Compared with the large-size counterpart, nickel molybdate ultrathin nanowires display promising oxygen evolution reaction catalytic performance derived from the ultrathin feature.

Dynamical changes of a Ni-Fe oxide water splitting catalyst investigated at different pH

Mixed Ni-Fe oxide electrocatalysts have shown high catalytic activity for the oxygen evolution reaction (OER) in alkaline electrolyte. Fundamental research on mixed Ni-Fe OER catalysts has largely focused on high pH, while the OER activity near neutral pH has remained poorly studied.Here we review the activity of an amorphous mixed Ni-Fe oxyhydroxide catalyst supported on carbon (NiFeOx/C) in 0.1M KOH pH 13, in 0.1M borate buffer (Bi) pH 9.2, and in 0.1M phosphate buffer (Pi) pH 7.0. The OER catalytic performance was found to decrease in the order of pH 13>pH 9.2>pH 7. In contrast to pH 13 and 9.2, the catalyst cycled in pH 7 showed an instantaneous decrease in OER activity and a simultaneous loss of the Ni(OH)2/NiOOH redox peak. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) showed the formation of crystalline areas upon CV cycling, which appeared more Ni enriched after cycling in pH 7. Deactivated electrodes cycled in pH 13 recovered the OER activity along with a partial reappearance of the Ni redox peak when subsequently cycled in pH 13. SEM-EDX spectroscopy confirmed compositional changes in the bulk during cycling at different pH, with an extensive leaching of Ni in pH 7. Our study provides new insight into the OER activity upon exposure to different electrolyte conditions, which unveils a highly dynamic Ni-Fe oxide framework.

Simple Chemical Solution Deposition of Co₃O₄ Thin Film Electrocatalyst for Oxygen Evolution Reaction.

Oxygen evolution reaction (OER) is the key reaction in electrochemical processes, such as water splitting, metal-air batteries, and solar fuel production. Herein, we developed a facile chemical solution deposition method to prepare a highly active Co3O4 thin film electrode for OER, showing a low overpotential of 377 mV at 10 mA/cm(2) with good stability. An optimal loading of ethyl cellulose additive in a precursor solution was found to be essential for the morphology control and thus its electrocatalytic activity. Our results also show that the distribution of Co3O4 nanoparticle catalysts on the substrate is crucial in enhancing the inherent OER catalytic performance.

First-Principles Study of Oxygen Evolution Reaction on the Oxygen-Containing Species Covered CoII-Exposing Co3O4 (100) Surface

The first-principles calculations were used to investigate the oxygen evolution reaction (OER) on the (100) surface of the spinel Co3O4, a high-performance oxidation catalyst. We compared the OER activities by the free-energy changes on three different covered surfaces including (i) clean, (ii) 0.5 monolayer O covered, and (iii) 0.5 monolayer OH covered surfaces, and the computed overpotential (η) for the three surfaces followed the order: O covered (η = 0.45 V) <OH covered (0.93 V) <clean (1.82 V). Furthermore, the influence of activities was analyzed by Bader charge, which showed that the Co Bader charge on the O/OH covered (100) surface was more than that on the clean surface. Based the above analysis, the O-containing species covered Co3O4 (100) surface exhibited better OER catalytic performance than that of the clean surface in the OER cycle.

Water Oxidation Electrocatalyzed by an Efficient Mn3O4/CoSe2Nanocomposite

The design of efficient, cheap, and abundant oxygen evolution reaction (OER) catalysts is crucial to the development of sustainable energy sources for powering fuel cells. We describe here a novel Mn(3)O(4)/CoSe(2) hybrid which could be a promising candidate for such electrocatalysts. Possibly due to the synergetic chemical coupling effects between Mn(3)O(4) and CoSe(2), the constructed hybrid displayed superior OER catalytic performance relative to its parent CoSe(2)/DETA nanobelts. Notably, such earth-abundant cobalt (Co)-based catalyst afforded a current density of 10 mA cm(-2) at a small overpotential of ~0.45 V and a small Tafel slope down to 49 mV/decade, comparable to the best performance of the well-investigated cobalt oxides. Moreover, this Mn(3)O(4)/CoSe(2) hybrid shows good stability in 0.1 M KOH electrolyte, which is highly required to a promising OER electrocatalyst.