Electrocatalyst For Oxidation Research Articles

Construction of transition metal/metal oxide synergistic with carbon nanomaterials trinity composites to promote electrocatalytic oxygen evolution

Novel non-precious metal electrocatalysts replace precious metal catalysts for water separation and are highly anticipated in commercial applications. The coexistence of crystalline and amorphous phases is thought to facilitate efficient electrocatalytic activity. In this work, a facile strategy is proposed to induce crystalline-amorphous core-shell nanocomposites via direct-current (DC) arc plasma technology. Heterogeneous crystalline amorphous nanocomposites (Fe/MnO@C) formed by coupling transition metal manganese oxide and magnetic iron into a carbon matrix exhibit excellent water oxidation properties. Spin-pinning effect is formed at the ferromagnetic metal/antiferromagnetic manganese oxide interface by controlled surface reconstruction. The established spin pinning effect can reduce the kinetic barriers in the OER (oxygen evolution reaction). The optimized Fe/MnO@C nanocomposite can be applied for OER in pH-universal electrolytes with low overpotential and small Tafel slope. The synergistic effects in an advantageous crystalline-amorphous core-shell nanocomposite significantly boost the reaction dynamics for water splitting. This research may shed light on the construction of high performance and low cost non-precious metal electrocatalysts for water oxidation.

Ni-W solid solution alloy as a high-performance catalyst for hydrazine electrooxidation

In the development of earth-abundant anodic electrocatalysts for direct hydrazine fuel cells (DHzFCs), one of the daunting challenges is to improve the electrocatalytic activity for the hydrazine oxidation reaction (HzOR) while effectively suppressing the non-faradaic decomposition of hydrazine. Herein, we present the synthesis of a Ni foam-supported Ni-W solid solution alloy (SSA) catalyst through a solvothermal approach followed by reductive calcination. Our study demonstrates that the Ni-W solid solution alloy outperforms intermetallic compound in simultaneously enhancing the electrocatalytic activity and inhibiting the non-faradaic hydrazine decomposition under alkaline conditions. Benefiting from its enhanced intrinsic activity, the open porous architecture, and good electrical conductivity, the Ni95W5(SSA)/NF catalyst has exhibited remarkable activity, good stability, and an impressive selectivity nearing 100 % towards the 4-electron hydrazine electrooxidation, surpassing most reported Ni-based alloy catalysts. Inspired by the exceptional catalytic performance, we have subsequently constructed a DHzFC utilizing Ni95W5(SSA) as the anode catalyst, and evaluated its performance under ambient temperature.

Unraveling the Dynamic Processes of Methanol Electrooxidation at Isolated Rhodium Sites by In Situ Electrochemical Scanning Tunneling Microscopy.

Materials with isolated single-atom Rh-N4 sites are emerging as promising and compelling catalysts for methanol electrooxidation. Herein, we carried out an in situ electrochemical scanning tunneling microscopy (ECSTM) investigation of the dynamic processes of methanol absorption and catalytic conversion in the rhodium octaethylporphyrin (RhOEP)-catalyzed methanol oxidation reaction at the molecular scale. The high-contrast RhOEP-CH3OH complex formed by methanol adsorption was visualized distinctly in the STM images. The Rh-C adsorption configuration of methanol on isolated rhodium sites was identified on the basis of a series of control experiments and theoretical simulation. The adsorption energy of methanol on RhOEP was obtained from quantitative analysis. In situ ECSTM experiments present an explicit description of the transformation of the intermediate species in the catalytic process. By qualitatively evaluating the rate constants of different stages in the reaction at the microscopic level, we considered the CO transformation/desorption as the critical step for determining the reaction dynamics. Methanol adsorption was found to be correlated with RhOEP oxidation in the initial stage of the reaction, and the dynamic information was revealed unambiguously by in situ potential step experiments. This work provides microscopic results for the catalytic mechanism of Rh-N4 sites for methanol electrooxidation, which is instructive for the rational design of the high-performance catalyst.

Modulating metal-oxygen interactions of high-entropy oxide electrocatalysts enables highly-active and ultra-stable water oxidation

High-entropy oxide (HEO) electrocatalysts are appealing for multi-step catalytic reactions as their high compositional diversity and multi-element synergy effects. Herein, we find that the metal-oxygen (M-O) interactions in FeCoNi-based HEO can be well-optimized by introducing Al and Ce elements. The in-situ electrochemistry-triggered Al leaching exposes abundant newly-formed active sites with greatly reduced energy difference between TM 3d and O 2p orbitals. This fact shows the enhancement of M-O covalency, which is further quantified by the Fe/Co/Ni charge calculations. The stronger M-O covalency greatly decreases the activation energy of water oxidation at Fe/Co/Ni sites and the barrier of electrical transfer. Furthermore, the Ce element downshifts the O 2p band center, effectively refraining lattice oxygen loss. These advantages enable a supersmall overpotential of 303.7 mV at 500 mA cm−2 that maintains 95.8 % even operating for 840 h, which is the best report for the HEOs to date.

Co2P–Ni3S2 Heterostructured Nanocrystals as Catalysts for Urea Electrooxidation and Urea-Assisted Water Splitting

Co₂P–Ni₃S₂ Heterostructured Nanocrystals as Catalysts for Urea Electrooxidation and Urea-Assisted Water Splitting

Unveiling the origin of activity in RuCoOx-anchored nitrogen-doped carbon electrocatalyst for high-efficiency hydrogen production and hydrazine oxidation using Raman spectroscopy

Hydrazine-assisted water electrolysis has gained much attention nowadays as an energy-saving strategy for the large-scale production of hydrogen fuel. Regardless, the synthesis of highly proficient bifunctional electrocatalysts remains a major challenge. Metal–organic frameworks (MOF) derived electrocatalysts have recently demonstrated excellent bifunctional activity in water electrolysis. Herein, we developed a new type of Ru-MOF on rod-like Co-MOF (Ru/Co-MOF) microstructures via a two-step solvothermal route. Subsequently, the Ru/Co-MOF was used as a precursor and self-template to synthesize an electrocatalytically active RuO2/Co3O4 anchored nitrogen-doped carbon (RuCoOx@NC) composite via a one-pot pyrolysis–oxidation strategy under atmospheric air. The RuCoOx@NC composite showed an ultralow overpotential of 44 mV for the hydrogen evolution reaction and 255 mV for the oxygen evolution reaction at 10 mA cm−2 in a 1 M KOH solution. Besides, the RuCoOx@NC composite exhibited an ultra-small working potential of − 0.040 V (vs. reversible hydrogen electrode (RHE)) for the hydrazine oxidation reaction at 10 mA cm−2 in a 1 M KOH/0.5 M hydrazine solution. The assembled RuCoOx@NC∥RuCoOx@NC membrane-free overall hydrazine splitting electrolyzer only required ultralow cell voltages of 0.063 and 0.505 V to produce 10 and 100 mA cm−2, with remarkable long-term stability, demonstrating its exceptional bifunctional activity. Ex situ Raman spectroscopy results indicate that both Co3O4 and RuO2 species contribute to the electrocatalytic activity of the RuCoOx@NC composite. This work suggests a potential strategy for developing bifunctional electrocatalytic materials for energy-saving hydrogen production to solve future energy demands.

Co-reduction assisted fabrication of PdCuTe nanowires for enhanced glycerol electrooxidation

High-performance electrocatalysts for glycerol oxidation are highly craved for the direct glycerol fuel cells. Herein, trinary PdCuTe nanowires with well-defined nanostructure was prepared through a co-reduction assisted approach with Te nanowires as the starting template. The addition of ascorbic acid is the key for introduction of Cu into the PdTeCu nanowires during synthesis. Electrochemical results revealed that the incorporation of Cu could enhance the performance for glycerol electrooxidation, which rendering the as-fabricated PdCuTe nanowires afford the highest current density of 61.1 mA cm−2. Owe to the improved electrooxidation kinetics and reduced charge transfer resistance, the resultant PdCuTe nanowires also demonstrated a better long-term stability. The synthetic strategy proposed herein is useful for the preparation of other materials, and the developed catalysts herein may also find wide applications in electrochemical-related fields.

Elucidating the Active Sites and Synergies in Water Splitting on Manganese Oxide Nanosheets on Graphite Support

AbstractPhotosystem II is nature's solution for driving the oxygen evolution reaction to oxidize water. A manganese‐oxide cluster is this protein's active center for water splitting, while the most efficient man‐made catalysts are costly noble metal‐based oxides. Facing the climate change, research on affordable and abundant electrocatalysts is crucial. To mimic the biological solution, manganese oxide nanosheets are synthesized and deposited on highly‐oriented pyrolytic graphite. This electrocatalyst is then examined with spectroscopic and electrochemical measurements, electrochemical noise scanning tunneling microscopy, and density functional theory calculations. The detailed investigation assigns the origin of its enhanced water‐splitting performance to detected activity at the nanosheet edges which the proposed mechanism explains further. Therefore, the results provide a blueprint for how to design efficient electrocatalysts for water oxidation with abundant materials.

Trimetallic Oxide Electrocatalyst for Enhanced Redox Activity in Zinc-Air Batteries Evaluated by In Situ Analysis.

Researchers are investigating innovative composite materials for renewable energy and energy storage systems. The major goals of this studies are i) to develop a low-cost and stable trimetallic oxide catalyst and ii) to change the electrical environment of the active sites through site-selective Mo substitution. The effect of Mo on NiCoMoO4 is elucidated using both in situ X-ray absorption spectroscopy and X-ray diffraction analysis. Also, density functional theory strategies show that NiCoMoO4 has extraordinary catalytic redox activity because of the high adsorption energy of the Mo atom on the active crystal plane. Further, it is demonstrated that hierarchical nanoflower structures of NiCoMoO4 on reduced graphene oxide can be employed as a powerful bifunctional electrocatalyst for oxygen reduction/evolution reactions in alkaline solutions, providing a small overpotential difference of 0.75V. Also, Zn-air batteries based on the developed bifunctional electrocatalyst exhibit outstanding cycling stability and a high-power density of 125.1mW cm-2 . This work encourages the use of Zn-air batteries in practical applications and provides an interesting concept for designing a bifunctional electrocatalyst.

Bioinspired multimetal electrocatalyst for selective methane oxidation

Bioinspired multimetal electrocatalyst for selective methane oxidation

BaRuO3 coated Ti plate as an efficient and stable electro-catalyst for water splitting reaction in alkaline medium

Water splitting using an electrochemical device to produce hydrogen fuel is a green and economic approach to solve the energy and environmental crisis. The realistic design of durable electro-catalysts and their synthesis using a simplistic technique is a great challenge to produce hydrogen by water electrolysis. Herein, we report a stable highly active barium ruthenium oxide (BRO) electro-catalysts over Ti plate using a soft chemical method at low temperature. The synthesized material shows facile hydrogen evolution reaction (HER) as well as oxygen evolution reaction (OER) in alkaline medium with over-potentials of 195 mV and 300 mV, respectively at a current density of 10 mA cm−2. The excellent stability lasts for at least 24 h without any degradation for both the HER and OER at the current density of 10 mA cm−2, inferring the practical applications of the material toward production of green hydrogen energy. Certainly, the synthesized catalyst is capable adequately for the overall water splitting at a cell voltage of 1.60 V at a current density of 10 mA cm−2 with an impressive stability for at least 24 h, showing a minimum loss of potential. Thus the present work contributes to the rational design of stable and efficient electro-catalysts for overall water splitting reaction in alkaline media.

Co-doped NiFe-LDH nanosheets arrays supported on nickel foam as an efficient oxygen evolution electrocatalysis

In the field of water electrolysis for hydrogen production, NiFe-layered double hydroxides (NiFe-LDH) is currently one of the most excellent oxygen evolution electrocatalyst. However, its application in this field is limited due to its low durability, low conductivity and few active sites. In this work, we present a Co-introduced fine-modulated NiFe-LDH performance strategy to construct Co-doped NiFe-LDH nanosheets arrays supported on nickel foam (Co-NiFe-LDH/NF). The optimized Co-NiFe-LDH/NF showed ultralow overpotentials at 211, 237, 261 and 281 mV at 50, 100, 200 and 300 mA cm−2 current densities, separately, with an extremely low Tafel slope (40 mV dec−1). The Co-NiFe-LDH/NF was highly stable during the constant current test, and the potential increased by only 10 and 13 mV after 100 h stability test at 200 and 300 mA cm−2. Notably, it also works stably at the 500 and 1000 mA cm−2 very high current densities, representing high potential of commercial application. The theoretical calculation showed that: (1) Introducing Co into NiFe-LDH can reduce the energy barrier of OH* conversion to O* and increase the activity of OER; (2) Considering the formation energy, Co is more likely to replace Fe site in NiFe-LDH than Ni site; (3) The energy barrier, differential charge and partial density of states analysis show that the best OER performance is obtained when the Fe-to-Co ratio of 2:1, and the theoretical calculation is consistent with the experimental verification. This work provides a simple and effective method for the design and construction of doping elements into NiFe-LDH electrocatalysts for efficient water oxidation, and promoted NiFe-LDH material application in commercial alkaline water electrolysis cell.

Hydrazine-Assisted Acidic Water Splitting Driven by Iridium Single Atoms.

Water splitting, an efficient technology to produce purified hydrogen, normally requires high cell voltage (>1.5V), which restricts the application of single atoms electrocatalyst in water oxidation due to the inferior stability, especially in acidic environment. Substitution of anodic oxygen evolution reaction (OER) with hydrazine oxidation reaction (HzOR) effectually reduces the overall voltage. In this work, the utilization of iridium single atom (Ir-SA/NC) as robust hydrogen evolution reaction (HER) and HzOR electrocatalyst in 0.5m H2 SO4 electrolyte is reported. Mass activity of Ir-SA/NC is as high as 37.02 A mgIr -1 at overpotential of 50mV in HER catalysis, boosted by 127-time than Pt/C. Besides, Ir-SA/NC requires only 0.39V versus RHE to attain 10mA cm-2 in HzOR catalysis, dramatically lower than OER (1.5V versus RHE); importantly, a superior stability is achieved in HzOR. Moreover, the mass activity at 0.5V versus RHE is enhanced by 83-fold than Pt/C. The in situ Raman spectroscopy investigation suggests the HzOR pathway follows *N2 H4 →*2NH2 →*2NH→2N→*N2 →N2 for Ir-SA/NC. The hydrazine assisted water splitting demands only 0.39V to drive, 1.25V lower than acidic water splitting.

Enhancing Water Oxidation Catalysis by Controlling Metal Cation Distribution in Layered Double Hydroxides

AbstractThe sluggish kinetics of the oxygen evolution reaction (OER), the limiting step of the electrochemical water splitting process, hinders the eventual commercialization of this important renewable energy strategy. Hence, the development of efficient electrocatalysts for this reaction is crucial. Multi‐metal‐based (hydr)oxides are promising OER electrocatalysts because the electronic interactions between multiple constituent metal cations can potentially enhance electrochemical performances. However, complex compositions may not always lead to positive synergistic effects. The appropriate distribution of the cations is also critical. However, the high dispersibility of cations in these hydroxides renders the control of their distribution challenging. Herein, an approach is reported to control the metal cation distribution in layered double hydroxides (LDHs) to improve their OER performances. Restacking of exfoliated NiFe and CoAl LDH nanosheets leads to electrochemical synergistic effects between different nanosheets. As far as it is known, the restacked LDH described herein exhibits the lowest overpotential (224 mV) and Tafel slope (34.26 mV dec−1) among reported powder‐type (hydr)oxide and alloy OER electrocatalysts with more than three different metal cations. Thus, a new design approach is suggested to enhance the electrochemical performances of LDHs.

Cation Incorporation into Copper Oxide Lattice at Highly Oxidizing Potentials.

Electrolyte cations can have significant effects on the kinetics and selectivity of electrocatalytic reactions. We show an atypical mechanism through which electrolyte cations can impact electrocatalyst performance─direct incorporation of the cation into the oxide electrocatalyst lattice. We investigate the transformations of copper electrodes in alkaline electrochemistry through operando X-ray absorption spectroscopy in KOH and Ba(OH)2 electrolytes. In KOH electrolytes, both the near-edge structure and extended fine-structure agree with previous studies; however, the X-ray absorption spectra vary greatly in Ba(OH)2 electrolytes. Through a combination of electronic structure modeling, near-edge simulation, and postreaction characterization, we propose that Ba2+ cations are directly incorporated into the lattice and form an ordered BaCuO2 phase at potentials more oxidizing than 200 mV vs the normal hydrogen electrode (NHE). BaCuO2 formation is followed by further oxidation to a bulk Cu3+-like BaxCuyOz phase at 900 mV vs NHE. Additionally, during reduction in Ba(OH)2 electrolyte, we find both Cu-O bonds and Cu-Ba scattering persist at potentials as low as -400 mV vs NHE. To our knowledge, this is the first evidence for direct oxidative incorporation of an electrolyte cation into the bulk lattice to form a mixed oxide electrode. The oxidative incorporation of electrolyte cations to form mixed oxides could open a new route for the in situ formation of active and selective oxidation electrocatalysts.

IrOx-MoO3 nano-heterostructure electrocatalysts for efficient acidic water oxidation

Rational design of Ir-based electrocatalyst with high performance and low cost remains as an urgent requirement to speed up the sluggish acidic water oxidation to produce hydrogen in renewable energy conversion and storage systems. In this work, the highly dispersed IrOx nanoparticles are fabricated on MoO3 sheets coated Ti meshes (c-IrOx-MoO3/Ti) as efficient electrocatalytic electrodes for acidic water oxidation. The heterogeneous c-IrOx-MoO3/Ti catalysts show much higher acidic oxygen evolution reaction activity (∼200 mV overpotentials at 10 mA cm−2) and long-term stability (longer than 130 h at 100 mA cm−2) with extremely low Ir content (∼28.35 μgIr cm−2) as compared to the IrOx/Ti and commercial IrO2 catalysts. The special intertwined formation of MoO3 sheets through electrodeposition effectively promotes the uniform dispersion of IrOx nanoparticles and the electrocatalytic performance. Theoretical calculations reveal that the electronic modulation on the MoO3-IrOx heterogeneous interface optimized the adsorbed energies for oxygen intermediates on the active Ir sites of the catalysts. The self-assembled proton exchange membrane single-cell electrolyzer test further verifies that the fabricated c-IrOx-MoO3/Ti catalysts demonstrate a greatly lower voltage and higher stability for water electrolysis than the commercial IrO2 catalysts. This work provides a new pathway to designing highly active and acid-resistant Ti-supported water oxidation catalysts with ultra-low Ir content.

Evaluating the functions of the key dopant elements in multi-metal oxide electrocatalysts for high-performance Li-O2 batteries

Multi-metal oxides (MMOs) have emerged as promising electrocatalysts for high-performance Li-O2 batteries (LOBs) because of their tailored intrinsic properties. However, the complex nature of MMOs, with multiple elements involved, has made it challenging to fully comprehend the electrochemical behaviour of MMOs in relation to the metal composition. Herein, we systematically synthesized a series of spinel MMOs, including Ni-Co-Fe, Mn-Co-Fe, and Ni-Mn-Fe oxides, by doping Ni, Co, or Mn into spinel Fe3O4 via a hydrothermal method. The properties of the obtained MMOs, including metal element cooperation, oxygen vacancy, and substitution positions of the metal cations, are carefully examined. We further evaluated the obtained MMOs as electrocatalysts in LOBs to investigate the dependency between their metal composition and electrocatalytic properties. Interestingly, we found the ratio of Fe3+/Fe2+ in the MMOs can be changed by matching different doping elements, affecting the cycling stability of LOBs with Fe-based MMOs. It is also revealed that Ni-Co-Fe oxides have stronger adsorption of O2 and LiO2 and better electrical conductivity than Mn-Co-Fe and Ni-Mn-Fe oxides. In addition, more oxygen vacancy in the crystal structure of MMOs can be obtained by doping more Ni and Co atoms, which facilitates electron/Li+ transportation and oxygen adsorption. With the increased amount of the doped Ni and Co in the Ni-Co-Fe oxides, the LOBs demonstrated an improved specific capacity from 8120 mAh g−1 to 10698 mAh g−1 at the same current density of 200 mA g−1. This systematic investigation of the MMO composition has provided a profound understanding of MMOs electrocatalysts, offering valuable insights for designing and optimizing MMO-based electrocatalysts for advanced LOBs.

CuO-SnO2 nanocomposites: Efficient and cost-effective electrocatalysts for urea oxidation

In this work, CuO–SnO2 (CS) nanocomposites with different amounts of urea (CS-1:0.9 g, CS-2:0.18 g, and CS-3:0.36 g) were synthesized using a facile hydrothermal method. CS-1 exhibited the best OER and UOR activity among the prepared electrocatalysts, with lower ovepotential 280 mV and Tafel slope of 229 mV dec−1 (OER@10 mA cm−2), and high electrochemically active surface area (39.4 mF cm−2) and lower charge transfer resistance. Furthermore, all the electrocatalysts demonstrated excellent stability (up to 10 h).

Ruthenium oxide/cobalt oxide heterojunction electrocatalyst for biomass-derivative oxidation and hydrogen evolution

Ruthenium oxide/cobalt oxide heterojunction electrocatalyst for biomass-derivative oxidation and hydrogen evolution

Fabrication of mesoporous CrTe supported on graphitic carbon nitride as an efficient electrocatalyst for water oxidation

It is essential to produce oxygen evolution reaction (OER) electrocatalysts, which are active and enduring for water electrolyzers. In order to create the effective OER, new chromium telluride/graphitic carbon nitride (gCN/CrTe) is produced via simple hydrothermal method. In this case, catalyst super hydrophilic surface is developed by the addition of 10% gCN nanosheets that can optimize the revelation of active sites and encourage the mass dispersion. Due to the robust contact among CrTe and gCN, which causes a lattice strain and an increase in the electron density around Cr sites, regulating the bonding between the catalyst and chemical intermediates. The improved 10% gCN/CrTe nanocomposite offers not only a good endurance but also by the highest mass activity. The synthesized 10% gCN/CrTe electrocatalysts provided low overpotential around 187 mV for OER to achieve a current density of 10 mA/cm2 in alkaline media with 51.0 h of long durability. Paving the way for innovative applications, this will enable the manipulation of advanced materials' fundamental properties at the atomic scale.