Yanmei Shi

Synthesis of ultrathin CdS nanosheets as efficient visible-light-driven water splitting photocatalysts for hydrogen evolution

Ultrathin CdS nanosheets with a thickness of ~4 nm have been synthesized through an ultrasonic-induced aqueous exfoliation method involving lamellar CdS-DETA hybrid nanosheets as starting materials and L-cysteine as a stabilizing agent. The as-obtained CdS ultrathin nanosheets exhibit efficient photocatalytic activity and good stability for hydrogen production.

Ni2P nanosheets/Ni foam composite electrode for long-lived and pH-tolerable electrochemical hydrogen generation.

The continuous consumption of fossil fuels and accompanying environmental problems are driving the exploration of low-cost and effective electrocatalysts to produce clean hydrogen. A Ni2P nanosheets/Ni foam composite, as a non-noble metal electrocatalyst, has been prepared through a facile chemical conversion pathway using surface oxidized Ni foam as precursor and low concentration of trioctylphosphine (TOP) as a phosphorus source. Further investigation shows the oxidized layer of Ni foam can orient the formation of Ni2P nanosheets and facilitate the reaction with TOP. The Ni2P/Ni, acting as a robust 3D self-supported superaerophobic hydrogen-evolving cathode, shows superior catalytic performance, stability, and durability in aqueous media over a wide pH value of 0-14, making it a versatile catalyst system for hydrogen generation. Such highly active, stable, abundant, and low-cost materials hold enormously promising potential applications in the fields of catalysis, energy conversion, and storage.

Self-template-directed synthesis of porous perovskite nanowires at room temperature for high-performance visible-light photodetectors.

The unique optoelectronic properties and promising photovoltaic applications of organolead halide perovskites have driven the exploration of facile strategies to synthesize organometal halide perovskites and corresponding hybrid materials and devices. Currently, the preparation of CH3 NH3 PbBr3 perovskite nanowires, especially those with porous features, is still a great challenge. An efficient self-template-directed synthesis of high-quality porous CH3 NH3 PbBr3 perovskite nanowires in solution at room temperature using the Pb-containing precursor nanowires as both the sacrificial template and the Pb(2+) source in the presence of CH3 NH3 Br and HBr is now presented. The initial formation of CH3 NH3 PbBr3 perovskite layers on the surface of the precursor nanowires and the following dissolution of the organic component of the latter led to the formation of mesopores and the preservation of the 1D morphology. Furthermore, the perovskite nanowires are potential materials for visible-light photodetectors with high sensitivity and stability.

In situ electrochemically converting Fe 2 O 3 -Ni(OH) 2 to NiFe 2 O 4 -NiOOH: a highly efficient electrocatalyst towards water oxidation

To develop low-cost, earth-abundant NiFebased materials as highly efficient oxygen evolution reaction (OER) electrocatalysts and to probe new catalytic species are still great challenges to now. Here, an in situ formation of OER active NiFe2O4-NiOOH nanosheet arrays is demonstrated as a highly efficient OER electrocatalyst by the anodization of Fe2O3 domains anchored on Ni(OH)2 nanosheet arrays. The as-converted product can deliver the current density of 30 mA cm−2 with a small overpotential of 240 mV, and only requires an overpotential of 410 mV to achieve an amazing huge current density of 3000 mA cm−2. In situ potential-dependent Raman spectroscopy reveals that Ni(OH)2 in the composite is easier to be oxidized to NiOOH than pure Ni(OH)2, and the newly formed NiOOH reacts with the nearby Fe2O3 to produce hybrid NiFe2O4-NiOOH. It is found that the cooperative effect of the in situ formed NiFe2O4 and NiOOH as well as the hydrophilic and aerophobic electrode surface make main contribution to the outstanding OER activity of the catalyst. This work will bring new perspectives to the recognition of the origin of NiFe composite materials for OER and provide a mild method to synthesize amorphous spinel materials at room temperature.摘要探索新的催化活性物种和开发价格低廉、来源广泛的镍铁基电催化剂对实现高效电解水产氧有着重要意义. 本文报道了一种通过 阳极化镶嵌Fe2O3颗粒的Ni(OH)2纳米片阵列, 使其原位电化学转化成NiFe2O4-NiOOH纳米片阵列用于高效电解水产氧的复合催化剂. 电化 学产氧测试表明: 这种复合材料催化剂在电流密度达到30 mA cm−2时仅需240 mV的过电势, 且只需要410 mV的过电势就可使电流密度达 到3000 mA cm−2. 电化学原位拉曼光谱测试表明: 这种镶嵌有Fe2O3颗粒的Ni(OH)2纳米片中的Ni(OH)2拥有更高的反应活性, 从而使其不仅 更容易氧化生成NiOOH, 同时新生成的NiOOH可以在正电流的刺激下与Fe2O3颗粒反应原位生成非晶的NiFe2O4-NiOOH复合材料. 该复合 材料的高电化学产氧活性主要归因于NiFe2O4和NiOOH的协同作用, 以及由于纳米片阵列结构所导致的超疏气与超亲水表面. 这项工作不 仅从全新的角度解读了镍铁基催化剂高电催化产氧活性的起源, 同时还提供了一种温和的室温合成方法用以制备具有非晶结构的尖晶石 类材料. 此外, 该项工作还有助于研究者关注异质催化剂在电催化过程中的物质转化行为, 从而更好地设计和发展新型高效催化体系.

N-doped graphene wrapped hexagonal metallic cobalt hierarchical nanosheet as a highly efficient water oxidation electrocatalyst

An N-doped graphene wrapped metallic Co nanosheet-on-nanosheet structure with a thickness of sub-4 nm and a high percentage of hexagonal Co phase as an efficient water oxidation electrocatalyst is presented. This sample exhibits an onset overpotential of 290 mV and performs comparably to RuO2 at high current density due to the unique hexagonal Co and the wrapped N-doped graphene.

Synergetic Transformation of Solid Inorganic–Organic Hybrids into Advanced Nanomaterials for Catalytic Water Splitting

The rational synthesis of advanced nanomaterials with well-defined structures has been intensively studied due to the remarkable properties and intriguing applications of the formed materials. Recently, inorganic-organic hybrids have been widely adopted as precursors for chemical transformations toward the preparation of diverse nanomaterials. Specifically, inorganic and organic species with nano/molecule/atom-scale distribution serve as self-templates and sacrificial agents, respectively, endowing the products with controlled morphologies, band gaps, defects, and spatial architectures. However, previous works have focused mostly on the transformation of porous coordination polymers, such as metal-organic frameworks (MOFs), which would produce daughter nanomaterials with the inherited structure of their parental hybrids. Moreover, conventional transformation strategies often encounter difficulties in simultaneously manipulating multiple structural parameters of the target materials. Therefore, a synergetic transformation strategy involving the simultaneous removal of organic components and the reconstruction of inorganic components to transform solid inorganic-organic hybrids into functional nanomaterials is developed. In this Account, we review recent advances in the utilization of solid inorganic-organic hybrids as precursors and their transformation into inorganic functional nanomaterials through a synergetic transformation strategy with an emphasis on understanding the conversion mechanism. The synergetic transformation strategy we discussed is categorized by organic component removal coupled with different methods for the reconstruction of inorganic components, including ion exchange, interfacial reaction, redox reaction and self-assembly. The key to a synergetic transformation strategy lies in the cooperation and/or competition among different transformation tools through dynamics and/or thermodynamics. By controlling the rate and position of the ion exchange reaction coupled with the removal of organics, a series of nanomaterials with designed band gaps and spatial architectures are produced from the solid inorganic-organic hybrid nanosheet-based precursors. The dissimilarity of organics removal between the inner and outer regions of hybrids induced by interfacial reaction is capable of producing controlled porous/hollow structures. For the coupling of a redox reaction with organics removal, the products of the decomposition of organics induce the in situ oxidation/reduction of inorganic components to generate defects and a porous structure. Along with organics removal, the self-assembly of inorganic components can be achieved to yield novel nanomaterials with hierarchical structures. Based on the understanding of the conversion mechanism, diverse advanced nanomaterials with elaborately designed structures are prepared by adopting appropriate precursors and synergetic transformation strategies. We then summarize the applications of the conversion products for photo(electro)/electrocatalytic water splitting. The precisely modulated structure can specifically improve photon adsorption, electron transport, catalytic activity and durability. Thus, the conversion products can be directly used as photo(electro)/electrocatalysts with high activities and cycling stabilities. Finally, we provide an outlook on the current challenges and promising opportunities in this research area. We believe that the advanced synergetic transformation strategy of solid inorganic-organic hybrids will open up a new avenue for the preparation of nanomaterials with fascinating performance.

Adjusting the electronic structure by Ni incorporation: a generalized in situ electrochemical strategy to enhance water oxidation activity of oxyhydroxides

An in situ electrochemical strategy is developed to convert semi-conductive β-FeOOH to OER-active semi-metallic Ni incorporated β-FeOOH. The sample exhibits an overpotential of 247 mV at 10 mA cm−2, which is much lower than those of pure β-FeOOH (400 mV) and RuO2 (258 mV). This strategy is also suitable for incorporating Ni into γ-FeOOH and CoOOH with enhanced OER activities.

Hydrogen evolution activity enhancement by tuning the oxygen vacancies in self-supported mesoporous spinel oxide nanowire arrays

The development of facile strategies to tune the oxygen vacancy (OV) content in transition metal oxides (TMOs) is paramount to obtain low-cost and stable electrocatalysts, but still highly challenging. Taking NiCo2O4 as a model system, we have experimentally established a facile calcination and electrochemical activation (EA) methodology to dramatically increase the concentration of OVs and provide theoretical insight into how the concentration of OVs affects the performance of spinel TMOs towards the electrochemical hydrogen evolution reaction (HER). A self-supported cathode of OV-rich NiCo2O4 nanowire arrays was found to exhibit higher HER activity and better stability in alkaline media than its counterparts with fewer OVs. The electrocatalytic HER activity was in good agreement with the increasing concentration of OVs in the studied samples. A large current density of 360 mA·cm–2 was reached with an overpotential of only 317 mV. Additionally, such a facile strategy was able to efficiently generate OVs in other TMOs (e.g., CoFe2O4 and NiFe2O4) for enhanced HER performance. In addition, our theoretical results suggest that the increasing OV concentration reduces the adsorption energy of water molecules and their dissociation energy barrier on the surface of the catalyst, thus leading to performance improvement of spinel TMOs toward the electrochemical HER. This work may open a new avenue to increase the concentration of OVs in TMOs in a controlled manner for promising applications in a variety of fields.

Diethylenetriamine-assisted hydrothermal synthesis of dodecahedral α-Fe2O3 nanocrystals with enhanced and stable photoelectrochemical activity

Dodecahedral α-Fe2O3 nanocrystals (D-hematite) were successfully synthesized through a hydrothermal method involving FeS-diethylenetriamine (FeS-DETA) hybrid nanosheets as starting materials. The photoanode made by assembling the as-obtained D-hematite on ITO substrates exhibited efficient photoelectrocatalytic water splitting activity and good stability in 1.0 M KOH aqueous solution under visible light irradiation.

Boosting ethanol electrooxidation via photothermal effect over palladium/reduced graphene oxide

A photothermal effect strategy to combine the model thermal material, namely, reduced graphene oxide with active species (palladium) was developed to greatly improve the activity and stability of ethanol electrooxidation reaction (EOR). The improvement can be ascribed to both accelerated reaction kinetics of EOR and promoted desorption of the toxic reaction intermediate COads from active palladium caused by the efficient light absorption and subsequent conversion to thermy of reduced graphene oxide. Additionally, this photothermally enhanced strategy was found to be suitable for electrooxidation reactions of other alcohols (e.g., ethylene glycol and glycerol).