Yanyong Wang

In Situ Exfoliated, Edge-Rich, Oxygen-Functionalized Graphene from Carbon Fibers for Oxygen Electrocatalysis

Metal-free electrocatalysts have been extensively developed to replace noble metal Pt and RuO2 catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in fuel cells or metal-air batteries. These electrocatalysts are usually deposited on a 3D conductive support (e.g., carbon paper or carbon cloth (CC)) to facilitate mass and electron transport. For practical applications, it is desirable to create in situ catalysts on the carbon fiber support to simplify the fabrication process for catalytic electrodes. In this study, the first example of in situ exfoliated, edge-rich, oxygen-functionalized graphene on the surface of carbon fibers using Ar plasma treatment is successfully prepared. Compared to pristine CC, the plasma-etched carbon cloth (P-CC) has a higher specific surface area and an increased number of active sites for OER and ORR. P-CC also displays good intrinsic electron conductivity and excellent mass transport. Theoretical studies show that P-CC has a low overpotential that is comparable to Pt-based catalysts, as a result of both defects and oxygen doping. This study provides a simple and effective approach for producing highly active in situ catalysts on a carbon support for OER and ORR.

Nanoparticle-Stacked Porous Nickel–Iron Nitride Nanosheet: A Highly Efficient Bifunctional Electrocatalyst for Overall Water Splitting

Nanoparticle-stacked porous Ni3FeN nanosheets were synthesized through a simple nitridation reaction of the corresponding LDHs. The nanosheet is composed of stacked nanoparticles with more active sites exposed for electrocatalytic reactions. Thus, it exhibited excellent oxygen evolution reaction performance having an extremely low overpotential of 223 mV at 10 mA/cm(2) and hydrogen evolution reaction property with a very low overpotential of 45 mV at 10 mA/cm(2). This electrocatalyst as bifunctional electrodes is used to overall water splitting in alkaline media, showing a high performance with 10 mA/cm(2) at a cell voltage of 1.495 V.

Water‐Plasma‐Enabled Exfoliation of Ultrathin Layered Double Hydroxide Nanosheets with Multivacancies for Water Oxidation

An earth-abundant and highly efficient electrocatalyst is essential for oxygen evolution reaction (OER) due to its poor kinetics. Layered double hydroxide (LDH)-based nanomaterials are considered as promising electrocatalysts for OER. However, the stacking structure of LDHs limits the exposure of the active sites. Therefore, the exfoliation is necessary to expose more active sites. In addition, the defect engineering is proved to be an efficient strategy to enhance the performance of OER electrocatalysts. For the first time, this study prepares ultrathin CoFe LDHs nanosheets with multivacancies as OER electrocatalysts by water-plasma-enabled exfoliation. The water plasma can destroy the electrostatic interactions between the host metal layers and the interlayer cations, resulting in the fast exfoliation. On the other hand, the etching effect of plasma can simultaneously and effectively produce multivacancies in the as-exfoliated ultrathin LDHs nanosheets. The increased active sites and the multivacancies significantly contribute to the enhanced electrocatalytic activity for OER. Compared to pristine CoFe LDHs, the as-exfoliated ultrathin CoFe LDHs nanosheets exhibit excellent catalytic activity for OER with a ultralow overpotential of only 232 mV at 10 mA cm-2 and possesses outstanding kinetics (the Tafel slope of 36 mV dec-1 ). This work provides a novel strategy to exfoliate LDHs and to produce multivacancies simultaneously as highly efficient electrocatalysts for OER.

Porous cobalt–iron nitride nanowires as excellent bifunctional electrocatalysts for overall water splitting

Designing highly active, earth-abundant and stable bifunctional electrocatalysts for both the oxygen (OER) and hydrogen (HER) evolution reactions is very crucial to overall water splitting. Herein, we developed nanoparticle-stacked porous Co3FeNx (NSP-Co3FeNx) nanowires as bifunctional electrocatalysts, exhibiting excellent OER and HER activity with a low overpotential of 222 mV at 20 mA cm-2 and 23 mV at 10 mA cm-2, respectively, due to their unique structural advantages with grain boundaries, defects and dislocations. Moreover, the electrocatalysts as bifunctional electrodes show a high performance with 10 mA cm-2 at a cell voltage of 1.539 V.

In situ confined synthesis of molybdenum oxide decorated nickel–iron alloy nanosheets from MoO42− intercalated layered double hydroxides for the oxygen evolution reaction

This work reports molybdenum oxide decorated NiFe alloy nanosheets with high OER activity by reducing MoO42− intercalated nickel–iron layered double hydroxides (LDHs). The presence of MoO42− successfully led to structural integrity, increase of active sites, and modification of the surface electronic properties of the NiFe alloy.

Engineering the coordination geometry of metal–organic complex electrocatalysts for highly enhanced oxygen evolution reaction

Designing highly efficient oxygen evolution reaction (OER) electrocatalysts is very important for various electrochemical devices. In this work, for the first time, we have successfully generated coordinatively unsaturated metal sites (CUMSs) in phytic acid–Co2+ (Phy–Co2+) based metal–organic complexes by engineering the coordination geometry with room-temperature plasma technology. The CUMSs can serve as active centers to catalyze the OER. The electron spin resonance and X-ray absorption spectra provide direct evidence that the coordination geometry is obviously modified with many CUMSs by the plasma treatment. The plasma treated Phy–Co2+ (P-Phy–Co2+) only requires an overpotential of 306 mV to reach 10 mA cm−2 on glassy carbon electrodes. When we expand this strategy to a CoFe bimetallic system, it only needs an overpotential of 265 mV to achieve 10 mA cm−2 with a small Tafel slope of 36.51 mV dec−1. P-Phy–Co2+ is superior to the state-of-the-art. Our findings not only provide alternative excellent OER electrocatalysts, but also introduce a promising principle to design advanced electrocatalysts by creating more CUMSs.

Rapidly engineering the electronic properties and morphological structure of NiSe nanowires for the oxygen evolution reaction

The oxygen evolution reaction (OER) is one of the most important reactions in a wide range of renewable energy technologies. It is important to develop highly efficient electrocatalysts for the OER due to its sluggish kinetics. The electronic properties and morphological structure of electrocatalysts can significantly affect their OER performance. Electrocatalysts with the morphology of nanosheets can expose more active sites which would enhance the OER activity. Here, we report an extremely simple and fast method to synthesize a NixFe1−xSe@Ni(Fe)OOH core–shell nanostructure with a nanosheet shell by a facile solvothermal selenization and ion exchange reaction. The NixFe1−xSe@Ni(Fe)OOH core–shell nanostructure gives an excellent catalytic activity toward the OER with an overpotential as low as 260 mV to reach a current density of 100 mA cm−2 and excellent electrochemical long-term stability in 1 M KOH solution. The enhanced OER activity can be attributed to the dual modulation of electronic properties and the morphological structure by Fe doping.

N, P-dual doped carbon with trace Co and rich edge sites as highly efficient electrocatalyst for oxygen reduction reaction

Oxygen reduction reaction (ORR) is key to fuel cells and metal-air batteries which are considered as the alternative clean energy. Various carbon materials have been widely researched as ORR electrocatalysts. It has been accepted that heteroatom doping and exposure of the edge sites can effectively improve the activity of carbon materials. In this work, we used a simple method to prepare a novel N, P-dual doped carbon-based catalyst with many holes on the surface. In addition, trace level Co doping in the carbon material forming Co–N–C active species can further enhance the ORR performance. On one hand, the doping can adjust the electronic structure of carbon atoms, which would induce more active sites for ORR. And on the other hand, the holes formed on the surface of carbon nanosheets would expose more edge sites and can improve the intrinsic activity of carbon. Due to the heteroatom doping and the exposed edge sites, the prepared carbon materials showed highly excellent ORR performance, close to that of commercial Pt/C.摘要本文使用有机分子配位聚合作用一步聚合、 碳化、 酸洗得到了一种N,P双掺杂碳材料. 其具有痕量掺杂的金属钴、 且具有更多活性边缘. X射线光电子能谱显示杂原子成功进入碳材料当中, 并且发现酸洗后钴的信号非常低, 证明酸洗后, 材料表面形成非常多的孔, 暴露出更多的边缘催化位点. 制备的碳材料具有大量催化活性位点, 因此表现出极其优异的电催化氧还原性能. 另外, 与Pt/C相比, 制备的多孔碳材料还具有较好的抗毒性与稳定性, 进一步显示了其在新能源电池领域的应用前景.

Recent Progress on Layered Double Hydroxides and Their Derivatives for Electrocatalytic Water Splitting

Abstract Layered double hydroxide (LDH)‐based materials have attracted widespread attention in various applications due to their unique layered structure with high specific surface area and unique electron distribution, resulting in a good electrocatalytic performance. Moreover, the existence of multiple metal cations invests a flexible tunability in the host layers; the unique intercalation characteristics lead to flexible ion exchange and exfoliation. Thus, their electrocatalytic performance can be tuned by regulating the morphology, composition, intercalation ion, and exfoliation. However, the poor conductivity limits their electrocatalytic performance, which therefore has motivated researchers to combine them with conductive materials to improve their electrocatalytic performance. Another factor hampering their electrocatalytic activity is their large lateral size and the bulk thickness of LDHs. Introducing defects and tuning electronic structure in LDH‐based materials are considered to be effective strategies to increase the number of active sites and enhance their intrinsic activity. Given the unique advantages of LDH‐based materials, their derivatives have been also used as advanced electrocatalysts for water splitting. Here, recent progress on LDHs and their derivatives as advanced electrocatalysts for water splitting is summarized, current strategies for their designing are proposed, and significant challenges and perspectives of LDHs are discussed.