Effective Oxygen Evolution Reaction Electrocatalysts Research Articles

Machine learning-accelerated prediction of overpotential of oxygen evolution reaction of single-atom catalysts

SummaryThe oxygen evolution reaction (OER) is a critical reaction for energy-related applications, yet suffers from its slow kinetics and large overpotential. It is desirable to develop effective OER electrocatalysts, such as single-atom catalysts (SACs). Here, we demonstrate machine learning (ML)-accelerated prediction of OER overpotential of all transition metals. Based on density functional theory (DFT) calculations of 15 species of SACs, we design a topological information-based ML model to map the OER overpotentials with atomic properties of the corresponding SACs. The trained ML model not only yields remarkable prediction precision (relative error of 6.49%) but also enables a 130,000-fold reduction of prediction time in comparison with pure DFT calculation. Furthermore, an intrinsic descriptor that correlates the overpotential of an SAC with its atomic properties is revealed. The approach and results from this study can be readily applicable to screen other SACs and significantly accelerate the design of high-performance catalysts for many other reactions.

Cactus-like NiCo2S4@NiFe LDH hollow spheres as an effective oxygen bifunctional electrocatalyst in alkaline solution

The high-performance non-precious electrocatalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial to the practical application of fuel cells and metal-air batteries. Herein, a novel cactus-like NiCo2S4@NiFe LDH hollow sphere assembled by one-dimensional (1D) NiFe LDH nanowires and two-dimensional (2D) NiFe LDH nanosheets on the NiCo2S4 hollow spheres is prepared by a facile hydrothermal method. The outer NiFe LDH nanowires and NiFe LDH nanosheets can effectively suppress the collapse and corrosion of inner NiCo2S4 hollow structure during long-term stability tests. The integration of the effective OER electrocatalyst NiFe LDH into NiCo2S4 to form heterostructures, as well as the strong electronic interaction between NiCo2S4 and NiFe LDH, can greatly boost both ORR and OER activities. Due to the above merits, the NiCo2S4@NiFe LDH achieves remarkably a small potential gap (ΔE = Ej=10-E1/2) of only 0.667 V. This work offers a facile strategy to design efficient catalysts with heterostructures.

Boosting Oxygen Evolution Reaction Using Defect Rich Ultra-Thin Ruthenium Oxide Nanosheets in Acidic Media

Hydrogen is regarded as the most promising energy carrier. The pure hydrogen produced from electrochemical water splitting by using renewable energy is the most attractive and effective approach.[1] In comparison to alkaline water electrolysis, proton exchange membrane water electrolyzers (PEMWEs) could operate at higher current densities, lower ohmic loss, more compact system design, faster system response and more stable towards load-cycling and shutdowns. [2] The sluggish kinetics of oxygen evolution reaction (OER) at the anode of PEMWEs has restricted its practical applications. To date, iridium (Ir) metal and its oxide are usually selected as the state-of-the-art catalyst for OER due to their robust and long-term durability under the harsh acidic conditions. Nevertheless, Ir is an extremely scarce element, and its price has been doubled in the past few years. The development of low cost and highly effective electrocatalyst for OER in an acidic medium is urgently needed but remains a great challenge.In this work, we have prepared an ultra-thin RuO2 nanosheets by a simple molten salt method. High resolution STEM results show that the as-prepared RuO2 nanosheets is about 1-2 nm in thickness and hold a large number of defects, like Ru vacancy, grain boundary and amorphous. Toward OER, the as-prepared RuO2 nanosheets demonstrate an outstanding OER activity in acidic electrolyte, with an overpotential of only 199 mV for reach the current density of 10 mA cm-2 geo at a catalyst loading of 125 μg cm-2 geo. At the overpotential of 230 mV, the specific and mass activities of RuO2 nanosheets electrode is up to 0.89 mA cm-2 oxide and 0.516 A mg-1 Ru, which is 14.9 and 80.5 times higher than that of commercial RuO2 catalyst, respectively. Density functional theory (DFT) calculations (Figure 2e and 2f) indicated that the Ru vacancy defect on RuO2 surface could servers as the highly active site for remarkably weaken the binding energies of *O as compared to that of *OOH, which decrease the energy gap between ΔGO and ΔGOOH and thus dramatic enhanced OER performance. We also applied the catalysts in a homemade PEMWE device, at the applied cell voltage of 1.65 V, the current density of the RuO2 nanosheets catalyst cell reaches 0.93 A cm-2, which is almost 3 times larger than that of the cell with commercial RuO2 catalyst (0.31 A cm-2) at the same conditions, demonstrating that the RuO2 nanosheets possess great potential toward developing high performance PEMWEs.This work is under progress. Meanwhile, further characterizations, including XRD, XPS and more detailed morphology and electrochemical performance characterization of the RuO2 nanosheets catalyst will be presented at the meeting.The work described in this paper was financially supported by the Shenzhen Clean Energy Research Institute (No. CERI-KY-2019-003), Shenzhen Peacock Plan (KQTD2016022620054656), Shenzhen Key Laboratory project (ZDSYS201603311013489), The authors acknowledge the assistance of SUSTech Core Research Facilities.

Prussian blue analog nanocubes tuning synthesis of coral-like Ni3S2@MIL-53(NiFeCo) core-shell nanowires array and boosting oxygen evolution reaction

Developing highly-efficient and robust electrocatalysts for oxygen evolution reaction (OER) is crucial to relieve energy crisis. Herein, a facile two-step method involving Prussian blue nanocubes as template is introduced to synthesize coral-like Ni3S2@MIL-53(NiFeCo) core-shell nanowires array as an excellent OER electrocatalyst. The metal sulfides as a core in the core-shell structure could effectively adjust the morphology of the metal-organic frameworks (MOFs) in the shell layer forming ultrathin 2D MOFs nanosheets. The synthesized Ni3S2@MIL-53(NiFeCo)/NF nanowires exhibit excellent activity, which needs overpotential of only 236 mV to drive high current density of 50 mA cm−2 in 1.0 M KOH. This excellent catalytic performance can be attributed to the following aspects: 1) The synergy between the metal sulfides and the MOF contributes substantially to the OER performance. 2) The compact three-dimensional nano-array structure increases the electrochemically active surface area of Ni3S2@MIL-53(NiFeCo)/NF nanowires, which promotes electrolyte permeation and gas overflow. 3) The tight integration of the vertically aligned nanowires structure with the conductive substrate ensures rapid electron transport and ultra-high structural stability of the electrode material. We anticipate that our research will extend the strategy for assembling advanced materials as an effective electrocatalyst for OER.

Constructing FeCoSe2/Co0.85Se heterostructure catalysts for efficient oxygen evolution

The slow kinetics and high cost of noble metal catalysts greatly hinder the oxygen evolution reaction (OER) in the application of large-scale oxygen production, as well as water splitting. In order to overcome this burgeoning issue, worldwide research efforts have been carried out to find alternative, and efficient electrocatalysts. Due to its cheap and abundant sources, FeCo-based materials are considered as better candidate electrocatalysts for OER. Herein, a nanocomposite catalyst consisting of FeCoSe2 nanoparticles and Co0.85Se nanosheets was synthesized via a one-pot hydrothermal method. The resultant FeCoSe2/Co0.85Se heterostructure catalysts can further used as a self-supported catalytic electrode to drive the OER, which exhibits the overpotential of 0.33 V at a current density of 10 mA cm−2 and Tafel slope of 50.8 mV dec−1. Raman spectroscopy was employed to explore the intrinsic active species of as-prepared hybrid catalyst during the OER process, and test result shows that metal selenides was acting as the precursor of the real reaction species. This work provides a possibility to develop cheap and effective OER electrocatalysts to replace the costly noble metal catalysts for OER in electrochemical devices.

Antiperovskite Nitrides CuNCo3-xVx: Highly Efficient and Durable Electrocatalysts for the Oxygen-Evolution Reaction.

Perovskite oxides have attracted much attention for enabling the oxygen-evolution reaction (OER) over the past decades. Nevertheless, their poor conductivity is still a barrier hindering their use. Herein, we report a catalyst prototype of Co-based antiperovskite nitrides CuNCo3-xVx (0 ≤ x ≤ 1) to be a highly effective OER electrocatalyst. The synthesized CuNCo3-xVx exhibits greatly enhanced activity and stability toward the OER in alkaline medium. The CuNCo2.4V0.6 shows a mere 235 mV of overpotential to reach 10 mA cm-2, which is comparable to that of Ir/C (232 mV). More importantly, the CuNCo2.4V0.6 is more durable than the conventional Ir/C catalyst. The CuNCo2.4V0.6 catalyst enabled a Zn-air battery to exhibit a cycle life of 143 h with a much higher cell efficiency. The V-substituted CuNCo2.4V0.6 provides a higher content of the desirable Co3+ species in the post-OER catalyst, which ensures a high activity over a long-term operation. With these enhanced effects enabled by the compositional flexibility of CuNCo3-xVx antiperovskite nitride, a feasible strategy for optimizing an electrocatalyst with tunable properties is provided.

Hierarchical Iron/Nickel-Based Sulfide Supported on Ni Foam As a Bifunctional Electrocatalyst for Efficient Overall Water Splitting

Water splitting, consisting of oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), has received great attention owing to the potential to provide future sustainable and renewing energy source. However, the kinetically sluggish process of OER at anode and HER at cathode requires highly active electrocatalysts to accelerate the both electrode reactions. Currently, nickel-based catalysts are widely regarded as an effective electrocatalyst for OER due to their low cost, high stability, good redox properties, and high electrocatalytic performance. Herein, iron/nickel-based sulfide supported on Ni foam were simply synthesized using two step hydrothermal method and was used as a bifunctional electrocatalyst for OER and HER. The iron/nickel-based sulfide only require the low overpotentials of as smaller as 281 and 222 mV for HER and OER, respectively, at current density of 50 mA cm−2 in 1 M KOH. Assembled as an electrolyzer for overall water splitting, this bifunctional catalyst also indicates excellent low onset potential of only 1.41 V and deliver a current density of 10 mA cm−2 at a very low cell voltage of 1.59 V. The outstanding electrochemical performance of iron/nickel-based sulfide on Ni foam is mainly attributed to the synergistic effect of the binary metal system, leading to increasing the electroconductivity, active surface area, and intrinsic catalytic activity. These iron/nickel-based sulfide materials can be widely applied to fabricating efficient energy conversion and storage.

Coupling interface constructions of NiO–Cr2O3 heterostructures for efficient electrocatalytic oxygen evolution

The oxygen evolution reaction is a key reaction in rechargeable metal air battery. Nickel oxide (NiO) nanoparticles are a potential low-cost oxygen evolution reaction (OER) electrocatalyst, and its catalytic activity and stability are still to be further improved. The construction of interfacial catalysts can improve their electrocatalytic activity. In this work, we report that nickel oxide (NiO) nanoclusters supported on chromium oxide (Cr2O3) nanosheets form a novel NiO–Cr2O3 heterostructure as an effective electrocatalyst for OER. Compared with pristine NiO and Cr2O3, NiO–Cr2O3 exhibits higher OER activity with smaller overpotential of 270 mV and lower Tafel slope of 30 mVdec−1, as well as durability under alkaline conditions. The X-ray photoelectron spectroscopy, In-situ Raman spectra and theoretical calculations reveal a source of high catalytic activity of NiO–Cr2O3. The results show that the activity site is located at Cr–Ni site of the NiO–Cr2O3. Due to the obvious charge transfer between Cr and Ni atoms at the interface, the change of Ni and Cr electronic structure reduces the adsorption energy of oxygen species and increases their catalytic activity. This work constructs a new Cr–Ni interface coupling method through NiO–Cr2O3 heterostructure, which provides a new strategy for designing new efficient and inexpensive OER catalysts.

Three-dimensional VOx/NiS/NF nanosheets as efficient electrocatalyst for oxygen evolution reaction

Developing effective and robust electrocatalysts that are applicable for intense conditions is promising for variable industrial oxygen evolution reaction (OER). Herein, we have developed a simple hydrothermal strategy to construct a three dimensional nanoflower-like VOx nanosheets (VOx/NiS/NF) that utilizes S-modified NF as substrate. NiS/NF can provide not only high-surface area for the growth of VOx but also better conductivity and stability derived from NiS. XRD shows the formation of amorphous VOx supported on NiS/NF. XPS confirms the existence and valence state of V, Ni and S. EDX and SEM elemental mapping reveal the composition and great distribution of V, O, Ni and S. SEM and TEM show that the thin VOx nanosheets covered on the surface of NiS/NF uniformly, which implying more exposed active sites. OER measurements display that VOx/NiS/NF has the outstanding catalytic activity with the lower overpotential (330 mV, 50 mA cm−2), smaller tafel slope (121 mV dec−1) and lower value of semicircle of EIS than VOx/NF. The modification of NF may be the key for enhancement performances for OER due to reduced charge transfer resistance. The strong durability of VOx/NiS/NF may be attributed to the tighter integration between VOx and NiS/NF in alkaline electrolytes. The impressive results may provide a new strategy to design suitable substrate with good dispersion and conductivity to prepare effective electrocatalysts for OER.

Co(OH)2 hollow nanoflowers as highly efficient electrocatalysts for oxygen evolution reaction

Abstract

A High‐Performance Binary Ni–Co Hydroxide‐based Water Oxidation Electrode with Three‐Dimensional Coaxial Nanotube Array Structure

Developing nanostructured Ni and Co oxides with a small overpotential and fast kinetics of the oxygen evolution reaction (OER) have drawn considerable attention recently because their theoretically high efficiency, high abundance, low cost, and environmental benignity in comparison with precious metal oxides, such as RuO2 and IrO2. However, how to increase the specific activity area and improve their poor intrinsic conductivity is still challenging, which significantly limits the overall OER rate and largely prevent their utilization. Thus, developing effective OER electrocatalysts with abundant active sites and high electrical conductivity still remains urgent. In this work, a scrupulous design of OER electrode with a unique sandwich‐like coaxial structure of the three‐dimensional Ni@[Ni(2+/3+)Co2(OH)6–7]x nanotube arrays (3D NNCNTAs) is reported. A Ni nanotube array with open end is homogeneous coated with Ni and Co co‐hydroxide nanosheets ([Ni(2+/3+)Co2(OH)6–7]x) and is employed as multifunctional interlayer to provide a large surface area and fast electron transport and support the outermost [Ni(2+/3+)Co2(OH)6–7]x layer. The remarkable features of high surface area, enhanced electron transport, and synergistic effects have greatly assured excellent OER activity with a small overpotential of 0.46 V at the current density of 10 mA cm−2 and high stability.

Reduced graphene oxide/CoSe2 nanocomposites: hydrothermal synthesis and their enhanced electrocatalytic activity

Reduced graphene oxide (RGO)/CoSe2 nanocomposites were synthesized by self-assembly of CoSe2/DETA (DETA: diethylenetriamine) onto the surface of graphene oxide (GO), followed by subsequent chemical reduction of GO during a hydrothermal process. The as-synthesized products were characterized by powder X-ray diffraction, energy dispersive X-ray spectroscopy, Raman spectra, scanning electron microscopy, and transmission electron microscopy. The morphology of the CoSe2 on the RGO nanosheets can be well controlled by adjusting the reaction time during the hydrothermal process. The catalytic activities of the RGO/CoSe2 nanocomposites were investigated for oxygen evolution reaction (OER) in alkaline conditions. It was found that the as-formed RGO/CoSe2 nanocomposites show higher catalytic activity compared with the unsupported CoSe2. In addition, the loading amounts and morphologies of CoSe2 on RGO sheets have a great influence on the catalytic performance of RGO/CoSe2. Our studies raise promising possibilities for designing effective OER electrocatalysts for energy conversion.