Modulating the d-Band Center of RuO2 via Ni Incorporation for Efficient and Durable Li-O2 batteries.

Rechargeable Li-O2 batteries (LOBs) are considered as one of the most promising candidates for new-generation energy storage devices. One of major impediments is the poor cycle stability derived from the sluggish reaction kinetics of unreliable cathode catalysts, hindering the commercial application of LOBs. Therefore, the rational design of efficient and durable catalysts is critical for LOBs. Optimizing surface electron structure via the negative shift of the d-band center offers a reasonable descriptor for enhancing the electrocatalytic activity. In this study, the construction of Ni-incorporating RuO2 porous nanospheres is proposed as the cathode catalyst to demonstrate the hypothesis. Density functional theory calculations reveal that the introduction of Ni atoms can effectively modulate the surface electron structure of RuO2 and the adsorption capacities of oxygen-containing intermediates, accelerating charge transfer between them and optimizing the growth pathway of discharge products. Resultantly, the LOBs exhibit a large discharge specific capacity of 19658 mA h g-1 at 200 mA g-1 and extraordinary cycle life of 791 cycles. This study confers the concept of d-band center modulation for efficient and durable cathode catalysts of LOBs.

Selective photoelectrochemical oxidation of glucose to glucaric acid by single atom Pt decorated defective TiO2.

Photoelectrochemical reaction is emerging as a powerful approach for biomass conversion. However, it has been rarely explored for glucose conversion into value-added chemicals. Here we develop a photoelectrochemical approach for selective oxidation of glucose to high value-added glucaric acid by using single-atom Pt anchored on defective TiO2 nanorod arrays as photoanode. The defective structure induced by the oxygen vacancies can modulate the charge carrier dynamics and band structure, simultaneously. With optimized oxygen vacancies, the defective TiO2 photoanode shows greatly improved charge separation and significantly enhanced selectivity and yield of C6 products. By decorating single-atom Pt on the defective TiO2 photoanode, selective oxidation of glucose to glucaric acid can be achieved. In this work, defective TiO2 with single-atom Pt achieves a photocurrent density of 1.91 mA cm-2 for glucose oxidation at 0.6 V versus reversible hydrogen electrode, leading to an 84.3 % yield of glucaric acid under simulated sunlight irradiation.

From Micropores to Ultra-micropores inside Hard Carbon: Toward Enhanced Capacity in Room-/Low-Temperature Sodium-Ion Storage.

HIGHLIGHTS: Hard-carbon anode dominated with ultra-micropores (< 0.5 nm) was synthesized for sodium-ion batteries via a molten diffusion-carbonization method. The ultra-micropores dominated carbon anode displays an enhanced capacity, which originates from the extra sodium-ion storage sites of the designed ultra-micropores. The thick electrode (~ 19 mg cm-2) with a high areal capacity of 6.14 mAh cm-2 displays an ultrahigh cycling stability and an outstanding low-temperature performance. Pore structure of hard carbon has a fundamental influence on the electrochemical properties in sodium-ion batteries (SIBs). Ultra-micropores (< 0.5 nm) of hard carbon can function as ionic sieves to reduce the diffusion of slovated Na+ but allow the entrance of naked Na+ into the pores, which can reduce the interficial contact between the electrolyte and the inner pores without sacrificing the fast diffusion kinetics. Herein, a molten diffusion-carbonization method is proposed to transform the micropores (> 1 nm) inside carbon into ultra-micropores (< 0.5 nm). Consequently, the designed carbon anode displays an enhanced capacity of 346 mAh g-1 at 30 mA g-1 with a high ICE value of ~ 80.6% and most of the capacity (~ 90%) is below 1 V. Moreover, the high-loading electrode (~ 19 mg cm-2) exhibits a good temperature endurance with a high areal capacity of 6.14 mAh cm-2 at 25 °C and 5.32 mAh cm-2 at - 20 °C. Based on the in situ X-ray diffraction and ex situ solid-state nuclear magnetic resonance results, the designed ultra-micropores provide the extra Na+ storage sites, which mainly contributes to the enhanced capacity. This proposed strategy shows a good potential for the development of high-performance SIBs.

Application of functionalized graphene in Li-O2 batteries.

Li-O2 batteries (LOB) are considered as one of the most promising energy storage devices using renewable electricity to power electric vehicles because of its exceptionally high energy density. Carbon materials have been widely employed in LOB for its light weight and facile availability. In particular, graphene is a suitable candidate due to its unique two-dimensional structure, high conductivities, large specific surface areas, and good stability at high charge potential. However, the intrinsic catalytic activity of graphene is insufficient for the sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in LOB. Therefore, various surface functionalization schemes for graphene have been developed to tailor the surface chemistry of graphene. In this review, the properties and performances of functionalized graphene cathodes are discussed from theoretical and experimental aspects, including heteroatomic doping, oxygen functional group modifications, and catalyst decoration. Heteroatomic doping breaks electric neutrality of sp2 carbon of graphene, which forms electron-deficient or electron-rich sites. Oxygen functional groups mainly create defective edges on graphene oxides with C-O, C=O, and -COO-. Catalyst decoration is widely attempted by various transition and precious metal and metal oxides. These induced reactive sites usually improve the ORR and/or OER in LOB by manipulating the adsorption energies of O2, LiO2, Li2O2, and promoting electron transportation of cathode. In addition, functionalized graphene is used in anode and separators to prevent shuttle effect of redox mediators and suppress growth of Li dendrite.

Potassium Doping Facilitated Formation of Tunable Superoxides in Li2O2 for Improved Electrochemical Kinetics.

Superoxide (O2-) species play a crucial role in determining the charge kinetics for aprotic lithium-oxygen (Li-O2) batteries. However, the growth of O2--rich lithium peroxide (Li2O2) is challenging since O2- is thermodynamically unfavorable and unstable in an O2 atmosphere. Herein, we reported the synthesis of defective Li2O2 with tunable O2- via K+ doping. The K+ dopants can successfully stabilize O2- species and induce the coordination of Li+ with O2-, leading to increased Li vacancies. Compared to the pristine Li2O2, the as-prepared defective Li2O2 can be charged at a lower overpotential in Li-O2 batteries, which is ascribed to further increased Li vacancies contributed by the depotassiation process at the onset of the charge process. Our findings suggest a new strategy to better control O2- species in Li2O2 by K+ dopants and provide insights into the K+ effects on charge mechanism in Li-O2 batteries.

Recent advances in understanding of the mechanism and control of Li2O2 formation in aprotic Li-O2 batteries.

Aprotic Li-O2 batteries represent promising alternative devices for electrical energy storage owing to their extremely high energy densities. Upon discharge, insulating solid Li2O2 forms on cathode surfaces, which is usually governed by two growth models, namely the solution model and the surface model. These Li2O2 growth models can largely determine the battery performances such as the discharge capacity, round-trip efficiency and cycling stability. Understanding the Li2O2 formation mechanism and controlling its growth are essential to fully realize the technological potential of Li-O2 batteries. In this review, we overview the recent advances in understanding the electrochemical and chemical processes that occur during the Li2O2 formation. In the beginning, the oxygen reduction mechanisms, the identification of O2-/LiO2 intermediates, and their influence on the Li2O2 morphology have been discussed. The effects of the discharge current density and potential on the Li2O2 growth model have been subsequently reviewed. Special focus is then given to the prominent strategies, including the electrolyte-mediated strategy and the cathode-catalyst-tailoring strategy, for controlling the Li2O2 growth pathways. Finally, we conclude by discussing the profound implications of controlling Li2O2 formation for further development in Li-O2 batteries.

Correction: Recent advances in understanding of the mechanism and control of Li2O2 formation in aprotic Li-O2 batteries.

Correction for 'Recent advances in understanding of the mechanism and control of Li2O2 formation in aprotic Li-O2 batteries' by Zhiyang Lyu et al., Chem. Soc. Rev., 2017, DOI: 10.1039/c7cs00255f.

Synthesis of porous CoMoO4 nanorods as a bifunctional cathode catalyst for a Li-O2 battery and superior anode for a Li-ion battery.

We report the synthesis of porous CoMoO4 nanorods and their applications in lithium oxygen (Li-O2) and lithium ion (Li-ion) batteries. The unique porous structures of CoMoO4 nanorods can promote the permeation of electrolyte and benefit the transport of lithium ion. When employed as the cathode catalyst for a Li-O2 battery, CoMoO4 nanorods deliver an improved discharge capacity (4680 mA h g-1), lower charge potential and better cycle stability (41 cycles at 500 mA h g-1 capacity limit) compared with the bare carbon. When employed as an anode in Li-ion batteries, CoMoO4 nanorods can retain a capacity of 603 mA h g-1 after 300 cycles (400 mA g-1) and exhibit excellent rate capability.