Lihan Zhang

A high-energy, full concentration-gradient cathode material with excellent cycle and thermal stability for lithium ion batteries

Ni-rich Li[Ni1−xMx]O2 (M = Co, Mn and Al) cathodes have shortcomings of poor thermal stability at the delithiated state and insufficient cycle performance, which are unsatisfied for commercial application in lithium ion batteries. Herein, a nickel-rich lithium transition-metal oxide with the full concentration-gradient structure is designed to overcome those problems. In the full concentration-gradient oxide, the nickel concentration decreases linearly, and the manganese concentration increases gradually, whereas the cobalt concentration remains constant from the center to the surface of each particle based on the energy disperse spectrum (EDS) analysis on the cross-section of a single particle. Firstly, the full concentration-gradient precursor is successfully prepared via a newly developed co-precipitation route. After lithiation at 800 °C, the as-prepared full concentration-gradient and normal oxides could be indexed to a typical layered structure with an Rm space group as detected by X-ray diffraction (XRD). Correspondingly, the full concentration-gradient layered oxide delivers more excellent cycle stability (especially at 55 °C), and thermal stability as compared with the normal layered oxide. It is also found that the Ni dissolution in the electrolyte is more serious, resulting in inferior cycle life for the normal layered oxide. Whereas, the outer layer of the full concentration-gradient oxide is much more stable, contributing to such excellent cycle and thermal stability.

Potential-Cycling Synthesis of Single Platinum Atoms for Efficient Hydrogen Evolution in Neutral Media

Abstract Single‐atom catalysts (SACs) have exhibited high activities for the hydrogen evolution reaction (HER) electrocatalysis in acidic or alkaline media, when they are used with binders on cathodes. However, to date, no SACs have been reported for the HER electrocatalysis in neutral media. We demonstrate a potential‐cycling method to synthesize a catalyst comprising single Pt atoms on CoP‐based nanotube arrays supported by a Ni foam, termed PtSA‐NT‐NF. This binder‐free catalyst is centimeter‐scale and scalable. It is directly used as HER cathodes, whose performances at low and high current densities in phosphate buffer solutions (pH 7.2) are comparable to and better than, respectively, those of commercial Pt/C. The Pt mass activity of PtSA‐NT‐NF is 4 times of that of Pt/C, and its electrocatalytic stability is also better than that of Pt/C. This work provides a large‐scale production strategy for binder‐free Pt SAC electrodes for efficient HER in neutral media.

WO3@α-Fe2O3 Heterojunction Arrays with Improved Photoelectrochemical Behavior for Neutral pH Water Splitting

Photoelectrochemical (PEC) water splitting on illuminated semiconductors plays an increasing role in alternative energy devices because of the need for clean and sustainable energy. However, the overall efficiency of the process is still very low and requires further improvement for widespread application. Herein, we report that the PEC performance of WO3 can be optimized by constructing a WO3@α‐Fe2O3 heterojunction nanosheet array to expand the spectral range of light absorption and promote photogenerated electron–hole separation/transfer. This heterojunction photoanode exhibit a pronounced photocurrent response of 1.66 mA cm−2, a high incident photon‐to‐current conversion efficiency of ∼73.7 % at 390 nm, and an excellent photostability of 100 %, all at 1.23 V versus reversible hydrogen electrode. Therefore, our approach has great potential for designing efficient hybrid photoanodes for PEC water‐splitting systems.

A new synthesis strategy towards enhancing the structure and cycle stabilities of the LiNi0.80Co0.15Al0.05O2 cathode material

To enhance the structural stability and electrochemical performances of the LiNi0.80Co0.15Al0.05O2 (LNCA) cathode material for Li-ion batteries, a new synthetic strategy (Al-compensation method) is proposed in this paper. The precursors Ni0.80Co0.15Alx(OH)0.95×2+3x (x ≤ 0.05) are prepared by a hydroxide co-precipitation method, and the final LNCA products are synthesized with the precursors and an additional (0.05 − x) mole ratio of Al(OH)3. This new strategy combines the advantages of co-precipitation and solid state reactions, avoiding the fast precipitation of Al3+ and the flocculent precipitate. As a result, stoichiometric LNCA materials with uniform element distribution are obtained. Compared with LNCA samples prepared by conventional processes, the samples prepared by the Al-compensation method exhibit a better layered structure and hexagonal ordering, lower cation mixing and therefore higher coulombic efficiency and more stable cycle performance. Besides, the influences of calcination temperatures (650, 750 and 850 °C) on the structure and electrochemical performance of LNCA cathodes are investigated in advance, and the reasons for these influences are preliminarily discussed.

Two-in-one solution using insect wings to produce graphene-graphite films for efficient electrocatalysis

Natural organisms contain rich elements and naturally optimized smart structures, both of which have inspired various innovative concepts and designs in human society. In particular, several natural organisms have been used as element sources to synthesize low-cost and environmentally friendly electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells and metal–air batteries, which are clean energy devices. However, to date, no naturally optimized smart structures have been employed in the synthesis of ORR catalysts, including graphene-based materials. Here, we demonstrate a novel strategy to synthesize graphene–graphite films (GGFs) by heating butterfly wings coated with FeCl3 in N2, in which the full power of natural organisms is utilized. The wings work not only as an element source for GGF generation but also as a porous supporting structure for effective nitrogen doping, two-dimensional spreading, and double-face exposure of the GGFs. These GGFs exhibit a half-wave potential of 0.942 V and a H2O2 yield of < 0.07% for ORR electrocatalysis; these values are comparable to those for the best commercial Pt/C and all previously reported ORR catalysts in alkaline media. This two-in-one strategy is also successful with cicada and dragonfly wings, indicating that it is a universal, green, and cost-effective method for developing high-performance graphene-based materials.

Stepped surface-rich copper fiber felt as an efficient electrocatalyst for the CO2RR to formate

Copper (Cu) electrocatalysts for the carbon dioxide reduction reaction (CO2RR) attract immense interest by virtue of their low cost, environmental suitability and the ability to produce diverse reduction products. However, to date, realizing high selectivity for formate on Cu electrocatalysts in water-based electrolytes remains a significant challenge. Herein, we first synthesized Cu fiber felt as an efficient and stable electrocatalyst for the CO2RR through a novel biomass carbon-templated route. Remarkably, the Cu fibers expose rich nano-scale stepped surfaces with the preferred {111} facets, endowing the Cu fiber felt with high catalytic activity for formate formation, whose faradaic efficiency reaches 71.1 ± 3.1% in aqueous potassium hydrogencarbonate solution. Meanwhile, the Cu fiber felt exhibits good stability over 390 min of electrolysis. The present work potentially provides a new avenue of surface nanostructure design for more efficient and selective Cu electrocatalysts for the CO2RR.