Oxygen Release Reaction Research Articles

Integrating surface modification to improve the electrochemical performance of Li-rich cathode materials

The co-existence of Vos and the Li3PO4 coating is conducive to facilitating Li+ diffusion, stabilizing lattice oxygen, and suppressing irreversible oxygen release and side reactions at the electrolyte/electrode interface.

BaCoO3-δ perovskite-type oxygen carrier for chemical looping air Separation, part Ⅱ: Design of the monolithic oxygen carriers

This work is the second part of the application of BaCoO3-δ perovskite as an oxygen carrier for chemical looping air separation (CLAS). In this paper, monolithic oxygen carriers were prepared by loading BaCoO3-δ powder perovskite onto cordierite ceramics. The oxygen release performance of the monolithic oxygen carriers was evaluated through experimentation on a fixed-bed reactor and simulated using computational fluid dynamics (CFD) numerical methods. The surface temperature variation, oxygen release efficiency, and the effect of the cross-section shape of the loading material were investigated. The results showed that the monolithic oxygen carrier primarily released O2 via the lattice oxygen of BaCoO3-δ perovskite during the reaction process, and the kinetic model for oxygen release and the reaction mechanism of the monolithic oxygen carrier were essentially identical to those of powder BaCoO3-δ perovskite. CFD simulation showed that the surface temperature of the monolithic oxygen carrier decreased and then increased as the oxygen release reaction proceeded. And the temperature on the centerline of the inner surface of the monolithic oxygen carrier was the lowest. The hexagonal monolithic oxygen carrier demonstrated the highest maximum temperature difference along the centerline of its inner surface, reaching 7.26 °C, whereas both square and triangular monolithic oxygen carriers exhibited a maximum temperature difference of 6.73 °C. The monolithic oxygen carriers exhibited the highest conversion rate at the inlet and the lowest at an axial length of 19 mm. Among them, the square-shaped oxygen carrier showed higher surface temperatures and conversion rates, achieving values of 0.830 and 0.814 at the inlet and axial length of 19 mm after a duration of 600 s. These findings suggest that a square cross-section shape is more suitable for loading materials.

Tuning Li2MnO3-Like Domain Size and Surface Structure Enables Highly Stabilized Li-Rich Layered Oxide Cathodes.

Severe capacity/voltage fading still poses substantial obstacles in the commercial applications of Li-rich layered oxides, which stems from the aggregation of Li2MnO3-like domains and unstable surface structure. Here, we report highly stabilized Co-free Li1.2Ni0.2Mn0.6O2 with uniformly dispersed Li2MnO3-like domains and a protective rock-salt structure shell by reducing the oxygen partial pressure during high-temperature calcination. Experimental characterizations and DFT calculations reveal that the uniformly dispersed and small-sized Li2MnO3-like domains suppress the peroxidation of lattice oxygen, enabling highly reversible oxygen redox and excellent structural stability. Moreover, the induced rock-salt structure shell significantly restrains lattice oxygen release, TM dissolution, and interfacial side reactions, thereby improving the interfacial stability and facilitating Li+ diffusion. Consequently, the obtained Li1.2Ni0.2Mn0.6O2 which was calcinated under an oxygen partial pressure of 0.1% (LNMO-0.1) delivers a high reversible capacity of 276.5 mAh g-1 at 0.1 C with superior cycling performance (a capacity retention rate of 85.4% after 300 cycles with a small voltage fading rate of 0.76 mV cycle-1) and excellent thermal stability. This work links the synthesis conditions with the domain structure and electrochemical performance of Li-rich cathode materials, providing some insights for designing high-performance Li-rich cathodes.

Ni3N@Ni juncture layer enabled performance enhanced electrocatalytic water oxidation

High-performance and cost-effective catalysts for water splitting are key components of hydrogen-based energy technologies. As a classical catalyst, NiFe-LDH is confirmed as the ideal answer to the dynamic slow oxygen release reactions (OER). While, how to take best advantage of the electrocatalyst came to a non-negligible challenge. Herein, NiFe-LDH/Ni3N@Ni/CP electrode was assembled with Ni3N@Ni as a juncture layer for optimized performance. An overpotential of only 233 mV was needed to drive a current density of 100 mA cm−2, with a very low Tafel slope of 25.8 mV dec-1 and excellent durability of 150 h. The superior performance was ascribed to the optimized conductivity, accelerated charge transfer kinetics and enlarged ECSA for the juncture layer of Ni3N@Ni. This work provides brand-new ideas for the rational design of electrodes for water splitting.

A Gradient Doping Strategy toward Superior Electrochemical Performance for Li-Rich Mn-Based Cathode Materials.

Lithium-rich layered oxides (LLOs) are concerned as promising cathode materials for next-generation lithium-ion batteries due to their high reversible capacities (larger than 250mA h g-1 ). However, LLOs suffer from critical drawbacks, such as irreversible oxygen release, structural degradation, and poor reaction kinetics, which hinder their commercialization. Herein, the local electronic structure is tuned to improve the capacity energy density retention and rate performance of LLOs via gradient Ta5+ doping. As a result, the capacity retention elevates from 73% to above 93%, and the energy density rises from 65% to above 87% for LLO with modification at 1 C after 200 cycles. Besides, the discharge capacity for the Ta5+ doped LLO at 5 C is 155mA h g-1 , while it is only 122mA h g-1 for bare LLO. Theoretical calculations reveal that Ta5+ doping can effectively increase oxygen vacancy formation energy, thus guaranteeing the structure stability during the electrochemical process, and the density of states results indicate that the electronic conductivity of the LLOs can be boosted significantly at the same time. This strategy of gradient doping provides a new avenue to improve the electrochemical performance of the LLOs by modulating the local structure at the surface.

Self-supporting and bifunctional Cu-based electrocatalysts with porous structures as superior working electrodes for alkaline water splitting

Self-supporting and bifunctional Cu-based electrocatalyst with a unique lamellar structure is fabricated, achieving a low oxygen release reaction potential and low hydrogen evolution reaction potential as well as remarkable durability.

Hydrothermal oxygen uncoupling of high-concentration biogas slurry over Cu-α-Fe2O3·α-MoO3 catalyst

A hydrothermal oxygen uncoupling (HTOU) method which combines aqueous phase reforming (APR) and oxygen uncoupling was proposed to treat biogas slurry (BS). Based on Le Chatelier's principle, this novel approach was constructed and realized by Cu–α-Fe2O3·α-MoO3 catalyst with van der Waals heterojunction-redox property. Additionally, the catalyst was synthesized by integrating a simple one-pot sol-gel method and thermal hydrogenating. Results indicated that the optimal removal efficiencies of non-purgeable organic carbon (NPOC) (76.29%), total nitrogen (TN) (45.56%), and ammonia nitrogen (AN) (29.03%) were achieved on the Cu–α-Fe2O3·α-MoO3 catalyst at 225.00 °C for 30.00 min, respectively. The significant performance of Cu–α-Fe2O3·α-MoO3 could be attributed to three aspects. (1) The α-MoO3 nanosheets with van der Waals heterostructures obtained at the calcination temperature of 600.00 °C, which can provide the superior performance of APR for hydrogen generation. (2) The adsorbed oxygen species were eliminated by thermal hydrogenating which had a surface passivation effect. (3) The effect of oxygen uncoupling in the lattice oxygen and gaseous oxygen release reaction was beneficial to the degradation of organic matter. Moreover, the reuse of catalysts studies further revealed that the deactivation of catalysts originated from carbon deposition of aromatic polymers and heavy metals oxides pollution. Overall, these findings disclosed that the HTOU could be a promising alternative to the treatment of high-concentration organic wastewater.

A Theoretical Study of the Oxygen Release Mechanisms of a Cu-Based Oxygen Carrier during Chemical Looping with Oxygen Uncoupling

The Cu-based oxygen carrier is a promising material in the chemical looping with oxygen uncoupling (CLOU) process, while its performance in the CLOU is significantly dependent on the oxygen release properties. However, the study of oxygen release mechanisms in CLOU is not comprehensive enough. In this work, the detailed oxygen release mechanisms of CuO(110) and CuO(111) are researched at an atomic level using the density functional theory (DFT) method, including the formation of O2, the desorption of O2 and the diffusion of O anion, as well as the analysis of the density of states. The results show that (1) the most favorable pathway for O2 formation and desorption occurs on the CuO(110) surface of O-terminated with energy barriers of 1.89 eV and 3.22 eV, respectively; (2) the most favorable pathway for O anion diffusion occurs in the CuO(110) slab with the lowest energy barrier of 0.24 eV; and (3) the total density of states for the O atoms in the CuO(110) slab shifts to a lower energy after an O vacancy formation. All of the above results clearly demonstrate that the CuO(110) surface plays a significantly important role in the oxygen release reaction, and the oxygen vacancy defect should be conducive to the reactivity of oxygen release in a Cu-based oxygen carrier.

First-principles-based multiscale modelling of heterogeneous CoO oxidation kinetics in high-temperature thermochemical energy storage

Metal oxides experiencing reversible oxygen release and uptake reactions involve the scale-span (surface→grain→particle→reactor) problem in a thermochemical energy storage reactor. This study developed a first-principles-based multiscale modelling to calculate the heterogeneous CoO oxidation kinetics. At the surface scale, density function theory (DFT) is used to compute the reaction mechanism, and the data from DFT calculation are integrated into the transition state theory (TST) to calculate the reaction rate constants. At the grain scale, a rate equation theory is proposed to couple the surface reaction with the lattice oxygen in bulk phase. At the particle scale, intraparticle diffusion and external diffusion of gas molecules are calculated by the effective factor and mass transfer coefficient. At the reactor scale, a two-phase fluidization model is adopted to describe the mass transfer of oxygen from bubble phase to emulsion phase. The model was used to simulate the oxidation kinetic characteristics of a newly prepared kaolin-supported Co-based oxide. The reaction mechanism and kinetic rates constants obtained from DFT and TST are directly used to predict the CoO oxidation kinetics instead of by fitting the experimental data. The oxidation kinetics were validated by comparing with the experimental data obtained using a micro-fluidized bed thermogravimetric analysis technology. Results show the oxidation will be fully finished within ~10 s in the temperature of 700–750 °C, and the reaction is first-order when the O2 partial pressure is within 21 vol%. The effect of particle size shows three-zone characteristics of chemical reaction and gas diffusion combined controlling mechanism. It is demonstrated the first-principle-based multiscale modelling can provide an accurate prediction of the CoO oxidation kinetics in thermochemical energy storage.

Building Homogenous Li2 TiO3 Coating Layer on Primary Particles to Stabilize Li-Rich Mn-Based Cathode Materials.

Li-rich Mn-based oxides (LRMOs) are promising cathode materials for next-generation lithium-ion batteries (LIBs) with high specific energy (≈900 Wh kg-1 ) because of anionic redox contribution. However, LRMOs suffer from issues such as irreversible release of lattice oxygen, transition metal (TM) dissolution, and parasitic cathode-electrolyte reactions. Herein, a facile, scalable route to build homogenous and ultrathin Li2 TiO3 (LTO) coating layer on the primary particles of LRMO through molten salt (LiCl) assisted solid-liquid reaction between TiO2 and Li1.08 Mn0.54 Co0.13 Ni0.13 O2 is reported. The prepared LTO-coated Li1.08 Mn0.54 Co0.13 Ni0.13 O2 (LTO@LRMO) exhibits 99.7% capacity retention and 95.3% voltage retention over 125 cycles at 0.2C, significantly outperforming uncoated LRMO. Combined characterizations of differential electrochemical mass spectrometry, in situ X-ray diffraction, and ex situ X-ray photoelectron spectroscopy evidence significantly suppressed oxygen release, phase transition, and interfacial reactions. Further analysis of cycled electrodes reveals that the LTO coating layer inhibits TM dissolution and prevents the lithium anode from TM crossover effect. This study expands the primary particle coating strategy to upgrade LRMO cathode materials for advanced LIBs.

Constructing stable surface structures enabling fast charging for Li-rich layered oxide cathodes

Li-rich Mn-based layered oxides (LLOs) exhibiting ultrahigh specific capacity larger than 250 mAh g−1 have become the most promising cathode candidate for high energy density lithium-ions batteries (LIBs). Fast charging capability and cycling stability are highly desirable for LIBs so as to satisfy specific application scenarios such as electric vehicles. However, stable cycling and fast charging properties are severely hindered by obstacles including irreversible oxygen release, structural degradation and poor reaction kinetics. In this work, an integrative and facile surface structures constructing strategy to achieve stable cycling and fast charging in LLOs was provided. Oxygen vacancies and double coating layers including lithium phosphate layer and spinel layer were constructed on the surface through ammonium dihydrogen phosphate (NH4H2PO4) pretreatment. The designed material with induced stable bi-phase coating layers delivers a high discharge specific capacity of 284.6 mAh g−1 at 0.1 C with an ultrahigh initial coulombic efficiency of 95.3% and excellent rate performance of 132.2 mAh g−1 at 10 C. Even after 100 cycles, it can display a remarkable capacity of 215.8 mAh g−1 under 1 C/1 C and 205.1 mAh g−1 under 3 C/1 C. The excellent fast charging performance and cycling stability can be attributed to accelerated Li+ transportation rate due to its surface ion conductive layer and surface spinel phase layer, as well as suppressed oxygen release, transition metals dissolution and electrolyte attack resulting from surface oxygen vacancies and dual protective layers.

A carbon dot‐based total green and self‐recoverable solid‐state electrochemical cell fully utilizing O2/H2O redox couple

AbstractElectrochemical cell can overcome the inherent intermittence of the renewable energy sources, thus showing great potentials in applications ranging from electrical energy storage to future smart grid. However, the current electrochemical cells could not achieve the “total green” feature by fully utilizing the clean and abundant O2/H2O redox couples due to the enormous overpotentials for both oxygen reduction reaction (ORR) and oxygen release reaction (OER). Herein, we report a “total green” electrochemical composite film cell based on carbon dots (CDots), which can realize both ORR and OER in the acid environment. The in‐air voltage generation (0.95 V, with a maximum power of 5.3 μW) relies on the multiple‐electron‐transfer redox chemical reaction between the two active components inside the composite film, that is, ORR/OER of CDots and the redox reaction of polyaniline (PANI) on the electrode and the resulting proton concentration gradient. Interestingly, the cell can be self‐recovered at low load, recharged by adding H2O2, or electrocharged at high load. We anticipate that current study may open up new opportunities for designing and developing total‐green energy storage and conversion systems for diverse applications.

Effect of Fluorine Substitution on the Electrochemical Property and Structural Stability of a Lithium-Excess Cation Disordered Rock-Salt CathodeSupported by National Natural Science Foundation of China (Grant Nos. 51602191 and 52072233), and the Beijing National Laboratory for Condensed Matter Physics.

Lithium-excess cation disordered rock-salt materials have received much attention because of their high-capacity as a candidate for cathodes for lithium-ion batteries. The ultra-high specific capacity comes from the coordinated charge compensation of both transition metal and lattice oxygen. However, the oxygen redox at high voltage usually leads to irreversible oxygen release, thereby degrading the structure stability and electrochemical performance. Lithium-excess Li1.14Ni0.57+0.5 x Ti0.19 – 0.5 x Mo0.10O2 – x F x (x = 0, 0.05, 0.10, 0.15, and 0.20) with different amounts of fluorine substitution were synthesized. Among them, Li1.14Ni0.620Ti0.140Mo0.10O1.85F0.15 exhibits a lower capacity decline, better rate performance, and lower structure damage. The effects of fluorine substitution on the electrochemical property and structural stability were systematic studied by x-ray photoelectron spectroscopy and in situ XRD etc. Results show that fluorine substitution reduces the average valence of the anion, allowing a larger proportion of low-valent redox active transition metals, increasing the transition metal redox capacity, inhibiting irreversible oxygen release and side reaction. Fluorine substitution further improves the structural stability and suppresses lattice deformation of the material.

Cycling mechanism of Li2MnO3: Li–CO2 batteries and commonality on oxygen redox in cathode materials

Summary Li2MnO3 has been considered to be a representative Li-rich compound with active debates on oxygen activities. Here, by evaluating the Mn and O states in the bulk and on the surface of Li2MnO3, we clarify that Mn(III/IV) redox dominates the reversible bulk redox in Li2MnO3, while the initial charge plateau is from surface reactions with oxygen release and carbonate decomposition. No lattice oxygen redox is involved at any electrochemical stage. The carbonate formation and decomposition indicate the catalytic property of the Li2MnO3 surface, which inspires Li-CO2/air batteries with Li2MnO3 acting as a superior electrocatalyst. The absence of lattice oxygen redox in Li2MnO3 questions the origin of the oxygen redox in Li-rich compounds, which is found to be of the same nature as that in conventional materials based on spectroscopic comparisons. These findings provide guidelines on understanding and controlling oxygen activities toward high-energy cathodes and suggest opportunities on using alkali-rich materials for catalytic reactions.

Oxygen-redox reactions in LiCoO2 cathode without O–O bonding during charge-discharge

Summary Oxygen activity in highly delithiated LiCoO2 is critical to fully utilizing the energy density of this high-tap-density cathode but still lacks a clear understanding. In this work, we combined the results of several experimental techniques, especially resonant inelastic X-ray scattering (RIXS) and neutron pair distribution function (NPDF) analysis, together with theoretical calculations to study this topic. Our results conclude that oxygen redox takes place globally in the lattice, rather than forming localized dimerization as previously thought. RIXS results directly reveal the reversible oxygen redox, and NPDF results show that the O–O pair distance is considerably shortened in the highly delithiated LiCoO2. Theoretical calculations indicate that no O–O bonding is formed in LiCoO2, in sharp contrast to the lithium-rich system in which O–O bonding does form. These results provide the rationale for achieving a reversible deep delithiation and high energy density for LiCoO2-based electrodes.

NiFe LDH@Super P Nanocomposite as an Efficient Electrocatalyst for Oxygen Evolution Reaction

NiFe LDH (Layered Double Hydroxide) is a promising electrocatalyst for oxygen release reaction (OER), which is currently receiving more and more attention. Here, we propose a simple method to enhance the OER activity of NiFe LDH supported on Super P. The NiFe LDH@Super P catalyst with a nanoflower nanostructure was successfully synthesized via pre-hydrothermal treatment method, which ensures the normal nucleation process of the highly active NiFe LDH precursor and significantly promote the full contact of NiFe LDH and Super P in the three-dimensional space. The as synthesized NiFe LDH@Super P-2h sample exhibited excellent OER performances in alkaline media, and the overpotential is only 260 mV at a current density of 10 mA · cm-2. The outstanding OER electrocatalytic reaction performance is attributed to the unique three-dimensional nanoflower structure and excellent composite effect with Super P, which provides more specific surface areas and enables efficient transfer of electrons between them. This research work provides a simple and effective method for developing non-precious metal-based OER catalysts to replace expensive precious metal catalysts.

Evaluation of oxygen uncoupling characteristics of oxygen carrier using micro-fluidized bed thermogravimetric analysis

• MFB-TGA was used to evaluate the CLOU characteristics of oxygen carriers. • Oxygen release rate measured by MFB-TGA are ~2 faster than that tested in Q500. • Oxygen uptake rate measured by MFB-TGA are ~4 faster than that tested in Q500. Oxygen uncoupling characteristics of a natural manganese ore and a perovskite-type oxide CaMn 0.5 Ti 0.37 5Fe 0.125 O 3 were studied by using a microfluidized bed thermogravimetric analysis (MFB-TGA) technology which is based on a real-time mass measurement of fluidizing particles inside a bubbling bed reactor. The chemical stability, kinetics of the oxygen release and uptake reactions and fluidization property were investigated and the experimental data measured by MFB-TGA were compared with the results in a regular TGA instrument (TGA Q500). The regular TGA Q500 results show the reactivity of both the manganese ore and perovskite oxide are stable for multi cycles, and the oxygen uncoupling capacity of the manganese ore is ~1.2% (mass) which is ~2 times higher than that of the perovskite oxide. However, the experimental results from the MFB-TGA indicated that there is a serious agglomeration for the manganese ore. A very important finding is that the reaction rate of oxygen release and oxygen uptake of the perovskite oxide measured by the MFB-TGA are ~2 and ~4 times faster than that of testedby the TGA Q500. We can conclude that MFB-TGA is a very useful tool to measure the reactivity stability and kinetics of oxygen carriers in high-throughput analysis instead of the regular TGA.

Probing Depth-Dependent Transition-Metal Redox of Lithium Nickel, Manganese, and Cobalt Oxides in Li-Ion Batteries.

Layered lithium nickel, manganese, and cobalt oxides (NMC) are among the most promising commercial positive electrodes in the past decades. Understanding the detailed surface and bulk redox processes of Ni-rich NMC can provide useful insights into material design options to boost reversible capacity and cycle life. Both hard X-ray absorption (XAS) of metal K-edges and soft XAS of metal L-edges collected from charged LiNi0.6Mn0.2Co0.2O2 (NMC622) and LiNi0.8Mn0.1Co0.1O2 (NMC811) showed that the charge capacity up to removing ∼0.7 Li/f.u. was accompanied with Ni oxidation in bulk and near the surface (up to 100 nm). Of significance to note is that nickel oxidation is primarily responsible for the charge capacity of NMC622 and 811 up to similar lithium removal (∼0.7 Li/f.u.) albeit charged to different potentials, beyond which was followed by Ni reduction near the surface (up to 100 nm) due to oxygen release and electrolyte parasitic reactions. This observation points toward several new strategies to enhance reversible redox capacities of Ni-rich and/or Co-free electrodes for high-energy Li-ion batteries.

Dielectric Polarization in Inverse Spinel-Structured Mg2 TiO4 Coating to Suppress Oxygen Evolution of Li-Rich Cathode Materials.

High-energy Li-rich layered cathode materials (≈900 Wh kg-1 ) suffer from severe capacity and voltage decay during cycling, which is associated with layered-to-spinel phase transition and oxygen redox reaction. Current efforts mainly focus on surface modification to suppress this unwanted structural transformation. However, the true challenge probably originates from the continuous oxygen release upon charging. Here, the usage of dielectric polarization in surface coating to suppress the oxygen evolution of Li-rich material is reported, using Mg2 TiO4 as a proof-of-concept material. The creation of a reverse electric field in surface layers effectively restrains the outward migration of bulk oxygen anions. Meanwhile, high oxygen-affinity elements of Mg and Ti well stabilize the surface oxygen of Li-rich material via enhancing the energy barrier for oxygen release reaction, verified by density functional theory simulation. Benefited from these, the modified Li-rich electrode exhibits an impressive cyclability with a high capacity retention of ≈81% even after 700 cycles at 2 C (≈0.5 A g-1 ), far superior to ≈44% of the unmodified counterpart. In addition, Mg2 TiO4 coating greatly mitigates the voltage decay of Li-rich material with the degradation rate reduced by ≈65%. This work proposes new insights into manipulating surface chemistry of electrode materials to control oxygen activity for high-energy-density rechargeable batteries.

Degradation and Aging Routes of Ni-Rich Cathode Based Li-Ion Batteries

Driven by the increasing plea for greener transportation and efficient integration of renewable energy sources, Ni-rich metal layered oxides, namely NMC, Li [Ni1−x−yCoyMnz] O2 (x + y ≤ 0.4), and NCA, Li [Ni1−x−yCoxAly] O2, cathode materials have garnered huge attention for the development of Next-Generation lithium-ion batteries (LIBs). The impetus behind such huge celebrity includes their higher capacity and cost effectiveness when compared to the-state-of-the-art LiCoO2 (LCO) and other low Ni content NMC versions. However, despite all the beneficial attributes, the large-scale deployment of Ni-rich NMC based LIBs poses a technical challenge due to less stability of the cathode/electrolyte interphase (CEI) and diverse degradation processes that are associated with electrolyte decomposition, transition metal cation dissolution, cation–mixing, oxygen release reaction etc. Here, the potential degradation routes, recent efforts and enabling strategies for mitigating the core challenges of Ni-rich NMC cathode materials are presented and assessed. In the end, the review shed light on the perspectives for the future research directions of Ni-rich cathode materials.