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Automatic differentiation is a key component in deep learning. This topic is well studied and excellent surveys such as Baydin et al. (2018) have been available to clearly describe the basic concepts. Further, sophisticated implementations of automatic differentiation are now an important part of popular deep learning frameworks. However, it is difficult, if not impossible, to directly teach students the implementation of existing systems due to the complexity. On the other hand, if the teaching stops at the basic concept, students fail to sense the realization of an implementation. For example, we often mention the computational graph in teaching automatic differentiation, but students wonder how to implement and use it. In this document, we partially fill the gap by giving a step by step introduction of implementing a simple automatic differentiation system. We streamline the mathematical concepts and the implementation. Further, we give the motivation behind each implementation detail, so the whole setting becomes very natural., Comment: 17 pages, 15 figures

As an advanced amorphous material, sp3 amorphous carbon exhibits exceptional mechanical, thermal and optical properties, but it cannot be synthesized by using traditional processes such as fast cooling liquid carbon and an efficient strategy to tune its structure and properties is thus lacking. Here we show that the structures and physical properties of sp3 amorphous carbon can be modified by changing the concentration of carbon pentagons and hexagons in the fullerene precursor from the topological transition point of view. A highly transparent, nearly pure sp3−hybridized bulk amorphous carbon, which inherits more hexagonal-diamond structural feature, was synthesized from C70 at high pressure and high temperature. This amorphous carbon shows more hexagonal-diamond-like clusters, stronger short/medium-range structural order, and significantly enhanced thermal conductivity (36.3 ± 2.2 W m−1 K−1) and higher hardness (109.8 ± 5.6 GPa) compared to that synthesized from C60. Our work thus provides a valid strategy to modify the microstructure of amorphous solids for desirable properties.

As an advanced amorphous material, sp3 amorphous carbon exhibits exceptional mechanical, thermal and optical properties, but it cannot be synthesized by using traditional processes such as fast cooling liquid carbon and an efficient strategy to tune its structure and properties is thus lacking. Here we show that the structures and physical properties of sp3 amorphous carbon can be modified by changing the concentration of carbon pentagons and hexagons in the fullerene precursor from the topological transition point of view. A highly transparent, nearly pure sp3−hybridized bulk amorphous carbon, which inherits more hexagonal-diamond structural feature, was synthesized from C70 at high pressure and high temperature. This amorphous carbon shows more hexagonal-diamond-like clusters, stronger short/medium-range structural order, and significantly enhanced thermal conductivity (36.3 ± 2.2 W m−1 K−1) and higher hardness (109.8 ± 5.6 GPa) compared to that synthesized from C60. Our work thus provides a valid strategy to modify the microstructure of amorphous solids for desirable properties.

The fabrication of porous structure in the ultrathin materials still faces high difficulties. In particular, the precise modulations in the porosity and size are highly challenging. In this work, we have introduced small molecules to overcome such a challenge. And this substantially contributes to the energy related applications, especially to the water-energy (WE) treatment. Electrocatalytic water-splitting is hindered by the sluggish kinetics of water oxidation, requiring efficient earth-abundant electrocatalysts for the oxygen evolution reaction (OER). Herein we demonstrate the robust OER activity by introducing metal and oxygen multivacancies in noble-metal-free layered double hydroxides (LDHs) through the specific electron-withdrawing organic molecule methyl-isorhodanate (CH3NCS). Our work reveals that the metal and oxygen vacancies endow NiFe LDH with enhanced electron transfer and modulate the H2O adsorption, thereby boosting the OER electrocatalytic properties. Remarkably, the best-performing laminar NiFe LDH nanosheets with metal and oxygen multivacancies (v-L-LDHs) show an ultra-low overpotential of 230 mV at 100 mA cm−2 and Tafel slope of 37.1 mV dec−1. Density functional theory (DFT) has revealed the improved OER performance is realized by the co-existence of metal and O vacancies in NiFe LDH, where the defective region activates the electroactivity of Ni sites and O sites to promote the electron transfer and intermediate transformation. The Fe sites play a key role to preserve the high electroactivity of the Ni sites in long-term applications. The superior OER performance underpins the high potential of the reported facile organic anchor strategy for designing and synthesizing advanced electrocatalysts in both LDH and other potential 2D layered materials.

Amorphous materials inherit short- and medium-range order from the corresponding crystal and thus preserve some of its properties while still exhibiting novel properties1,2. Due to its important applications in technology, amorphous carbon with sp2 or mixed sp2–sp3 hybridization has been explored and prepared3,4, but synthesis of bulk amorphous carbon with sp3 concentration close to 100% remains a challenge. Such materials inherit the short-/medium-range order of diamond and should also inherit its superior properties5. Here, we successfully synthesized millimetre-sized samples—with volumes 103–104 times as large as produced in earlier studies—of transparent, nearly pure sp3 amorphous carbon by heating fullerenes at pressures close to the cage collapse boundary. The material synthesized consists of many randomly oriented clusters with diamond-like short-/medium-range order and possesses the highest hardness (101.9 ± 2.3 GPa), elastic modulus (1,182 ± 40 GPa) and thermal conductivity (26.0 ± 1.3 W m−1 K−1) observed in any known amorphous material. It also exhibits optical bandgaps tunable from 1.85 eV to 2.79 eV. These discoveries contribute to our knowledge about advanced amorphous materials and the synthesis of bulk amorphous materials by high-pressure and high-temperature techniques and may enable new applications for amorphous solids.

The fabrication of porous structure in the ultrathin materials still faces high difficulties. In particular, the precise modulations in the porosity and size are highly challenging. In this work, we have introduced small molecules to overcome such a challenge. And this substantially contributes to the energy related applications, especially to the water-energy (WE) treatment. Electrocatalytic water-splitting is hindered by the sluggish kinetics of water oxidation, requiring efficient earth-abundant electrocatalysts for the oxygen evolution reaction (OER). Herein we demonstrate the robust OER activity by introducing metal and oxygen multivacancies in noble-metal-free layered double hydroxides (LDHs) through the specific electron-withdrawing organic molecule methyl-isorhodanate (CH3NCS). Our work reveals that the metal and oxygen vacancies endow NiFe LDH with enhanced electron transfer and modulate the H2O adsorption, thereby boosting the OER electrocatalytic properties. Remarkably, the best-performing laminar NiFe LDH nanosheets with metal and oxygen multivacancies (v-L-LDHs) show an ultra-low overpotential of 230 mV at 100 mA cm−2 and Tafel slope of 37.1 mV dec−1. Density functional theory (DFT) has revealed the improved OER performance is realized by the co-existence of metal and O vacancies in NiFe LDH, where the defective region activates the electroactivity of Ni sites and O sites to promote the electron transfer and intermediate transformation. The Fe sites play a key role to preserve the high electroactivity of the Ni sites in long-term applications. The superior OER performance underpins the high potential of the reported facile organic anchor strategy for designing and synthesizing advanced electrocatalysts in both LDH and other potential 2D layered materials.

This article conducts an empirical study on the correlation between Chinese pork price and the fluctuation of the pork concept index. The first is to use Tushare financial data interface, crawler tools and other technologies to obtain initial data, then use machine learning SVM sentiment analysis to convert text data into structured data to pre-process and standardize the data, which is beneficial to SPSS.24 for correlation and multiple linear regression analysis. Finally came to the following conclusions: Firstly, the Chinese pork price has a significant positive correlation at the level of 0.01 with the pork concept index, and upstream and midstream companies in the pork industry chain are more affected by changes in pork prices. Therefore, investors can focus on pork price changes to guide investment decisions. Secondly, from the long-term analysis, investor sentiment has little effect on the stock price of pork stocks. Thirdly, weak correlation between Chinese macroeconomic factors and Chinese pork stock price.

This article conducts an empirical study on the correlation between Chinese pork price and the fluctuation of the pork concept index. The first is to use Tushare financial data interface, crawler tools and other technologies to obtain initial data, then use machine learning SVM sentiment analysis to convert text data into structured data to pre-process and standardize the data, which is beneficial to SPSS.24 for correlation and multiple linear regression analysis. Finally came to the following conclusions: Firstly, the Chinese pork price has a significant positive correlation at the level of 0.01 with the pork concept index, and upstream and midstream companies in the pork industry chain are more affected by changes in pork prices. Therefore, investors can focus on pork price changes to guide investment decisions. Secondly, from the long-term analysis, investor sentiment has little effect on the stock price of pork stocks. Thirdly, weak correlation between Chinese macroeconomic factors and Chinese pork stock price.

This article conducts an empirical study on the correlation between Chinese pork price and the fluctuation of the pork concept index. The first is to use Tushare financial data interface, crawler tools and other technologies to obtain initial data, then use machine learning SVM sentiment analysis to convert text data into structured data to pre-process and standardize the data, which is beneficial to SPSS.24 for correlation and multiple linear regression analysis. Finally came to the following conclusions: Firstly, the Chinese pork price has a significant positive correlation at the level of 0.01 with the pork concept index, and upstream and midstream companies in the pork industry chain are more affected by changes in pork prices. Therefore, investors can focus on pork price changes to guide investment decisions. Secondly, from the long-term analysis, investor sentiment has little effect on the stock price of pork stocks. Thirdly, weak correlation between Chinese macroeconomic factors and Chinese pork stock price.

This article conducts an empirical study on the correlation between Chinese pork price and the fluctuation of the pork concept index. The first is to use Tushare financial data interface, crawler tools and other technologies to obtain initial data, then use machine learning SVM sentiment analysis to convert text data into structured data to pre-process and standardize the data, which is beneficial to SPSS.24 for correlation and multiple linear regression analysis. Finally came to the following conclusions: Firstly, the Chinese pork price has a significant positive correlation at the level of 0.01 with the pork concept index, and upstream and midstream companies in the pork industry chain are more affected by changes in pork prices. Therefore, investors can focus on pork price changes to guide investment decisions. Secondly, from the long-term analysis, investor sentiment has little effect on the stock price of pork stocks. Thirdly, weak correlation between Chinese macroeconomic factors and Chinese pork stock price.

This article conducts an empirical study on the correlation between Chinese pork price and the fluctuation of the pork concept index. The first is to use Tushare financial data interface, crawler tools and other technologies to obtain initial data, then use machine learning SVM sentiment analysis to convert text data into structured data to pre-process and standardize the data, which is beneficial to SPSS.24 for correlation and multiple linear regression analysis. Finally came to the following conclusions: Firstly, the Chinese pork price has a significant positive correlation at the level of 0.01 with the pork concept index, and upstream and midstream companies in the pork industry chain are more affected by changes in pork prices. Therefore, investors can focus on pork price changes to guide investment decisions. Secondly, from the long-term analysis, investor sentiment has little effect on the stock price of pork stocks. Thirdly, weak correlation between Chinese macroeconomic factors and Chinese pork stock price.

This article conducts an empirical study on the correlation between Chinese pork price and the fluctuation of the pork concept index. The first is to use Tushare financial data interface, crawler tools and other technologies to obtain initial data, then use machine learning SVM sentiment analysis to convert text data into structured data to pre-process and standardize the data, which is beneficial to SPSS.24 for correlation and multiple linear regression analysis. Finally came to the following conclusions: Firstly, the Chinese pork price has a significant positive correlation at the level of 0.01 with the pork concept index, and upstream and midstream companies in the pork industry chain are more affected by changes in pork prices. Therefore, investors can focus on pork price changes to guide investment decisions. Secondly, from the long-term analysis, investor sentiment has little effect on the stock price of pork stocks. Thirdly, weak correlation between Chinese macroeconomic factors and Chinese pork stock price.

This article conducts an empirical study on the correlation between Chinese pork price and the fluctuation of the pork concept index. The first is to use Tushare financial data interface, crawler tools and other technologies to obtain initial data, then use machine learning SVM sentiment analysis to convert text data into structured data to pre-process and standardize the data, which is beneficial to SPSS.24 for correlation and multiple linear regression analysis. Finally came to the following conclusions: Firstly, the Chinese pork price has a significant positive correlation at the level of 0.01 with the pork concept index, and upstream and midstream companies in the pork industry chain are more affected by changes in pork prices. Therefore, investors can focus on pork price changes to guide investment decisions. Secondly, from the long-term analysis, investor sentiment has little effect on the stock price of pork stocks. Thirdly, weak correlation between Chinese macroeconomic factors and Chinese pork stock price.

We demonstrate the construction of heterojunction arrays for boosting solar water splitting by combining in situ guided growth of heterointerfaces and energy band tuning. By directly growing an ultrathin Fe2WO6 layer on a preformed WO3 nanosheet array in full coverage, a uniform and dense array of intimately contacted WO3/Fe2WO6 heterojunction was created. The heterojunction array shows not only a largely broadened visible light absorption range but also a built-in interface polarization to accelerate hole transfer from WO3 to Fe2WO6. Meanwhile, fine-tuning to match energy levels at the heterojunction was achieved by doping WO3 with Fe (Fe-WO3), leading to improved electrical conductivity and reduced charge recombination. Photoanodes based on such heterojunction arrays have shown significantly enhanced photoelectrochemical (PEC) water splitting performance, clearly arising from the above-mentioned efforts. Furthermore, by decorating FeOOH/NiOOH cocatalysts on the heterojunction arrays in tandem, the surface water oxidation kinetics was considerably accelerated, and the resulting Fe-WO3/Fe2WO6/FeOOH/NiOOH photoanode achieved a photocurrent density of 2.78 mA/cm(2) at 1.23 V vs reversible hydrogen electrode. This work highlights the benefits of in situ construction of heterojunction arrays for enhancing the PEC performance.

Solar water splitting using photoelectrochemical (PEC) cells has emerged as one of the most promising routes to produce hydrogen as a clean and renewable fuel source. The functional semiconductor materials and efficient nanostructures are the key to realizing the green hydrogen economy. My thesis research is directed at designing and constructing sustainable semiconductor materials and nanostructures for efficient and stable solar water splitting. Firstly, I developed new functional photoelectrodes and heterogeneous composites to boost the solar water splitting, including (1) the design and fabrication of the p-type ZnPbO3 and n-type Zn2PbO4 as the new photoelectrodes for water reduction and oxidation, respectively. Additionally, it was the first time that unassisted solar water splitting was realized by combining the CoPi/Zn2PbO4 photoanode and the MoS2/ZnPbO3 photocathode. (2) the configuration of BiVO4/BiFeO3 composite with regulable polarization electric field, which achieved with synergistic ferroelectric and piezoelectric effects, accelerating the interfacial charge separation and transfer in heterojunction structure for PEC applications. Secondly, I applied various strategies to fabricate the nanostructured photoelectrodes to high performance and stability hybrid PEC systems, including (1) the novel strategy to extend the cocatalyst loading from 1D to 3D from the photoabsorbing semiconductor (PAS) in a cross-linked conducting polymer network. This scheme has been proved to greatly increase the redox reaction sites without decreasing the light absorption and effectively prohibit charge recombination. (2) in-situ growth strategy to form the intertwined nanointerfaces with uniform, continuous, fully engaged connection of the adjacent constituents. Meanwhile, the charge transfer direction has been further enforced through band structure tuning to make the photogener

We demonstrate the construction of heterojunction arrays for boosting solar water splitting by combining in situ guided growth of heterointerfaces and energy band tuning. By directly growing an ultrathin Fe2WO6 layer on a preformed WO3 nanosheet array in full coverage, a uniform and dense array of intimately contacted WO3/Fe2WO6 heterojunction was created. The heterojunction array shows not only a largely broadened visible light absorption range but also a built-in interface polarization to accelerate hole transfer from WO3 to Fe2WO6. Meanwhile, fine-tuning to match energy levels at the heterojunction was achieved by doping WO3 with Fe (Fe-WO3), leading to improved electrical conductivity and reduced charge recombination. Photoanodes based on such heterojunction arrays have shown significantly enhanced photoelectrochemical (PEC) water splitting performance, clearly arising from the above-mentioned efforts. Furthermore, by decorating FeOOH/NiOOH cocatalysts on the heterojunction arrays in tandem, the surface water oxidation kinetics was considerably accelerated, and the resulting Fe-WO3/Fe2WO6/FeOOH/NiOOH photoanode achieved a photocurrent density of 2.78 mA/cm(2) at 1.23 V vs reversible hydrogen electrode. This work highlights the benefits of in situ construction of heterojunction arrays for enhancing the PEC performance.

Due to the limitation of the drone's load capacity, various specific tasks need to be accomplished by multiple drones in collaboration. In some transportation tasks, two drones are required to lift the load together, which brings even more significant challenges to the control problem because the transportation system is underactuated and it contains very complex dynamic coupling. When transporting bar-shaped objects, the load's attitude, the rope's swing motion, as well as the distance between the drones, should be carefully considered to ensure the security of the system. So far, few works have been implemented for double drone transportation systems to guarantee their transportation performance, especially in the aforementioned aspect. In this paper, a nonlinear cooperative control method is proposed, with both rigorous stability analysis and experimental results demonstrating its great performance. Without the need to distinguish the identities between the leader and the follower, the proposed method successfully realizes effective control for the two drones separately, mainly owning to the deep analysis for the system dynamics and the elaborate design for the control law. By utilizing Lyapunov techniques, the proposed controller achieves simultaneous positioning and mutual distance control of the drones, meanwhile, it efficiently eliminates the swing of the load. Flight experiments are presented to demonstrate the performance of the proposed nonlinear cooperative control strategy., Comment: 13 pages, original complete manuscript

Currently, in addition to the electroactive non-noble metal water-splitting electrocatalysts, a scalable synthetic route and simple activity enhancement strategy is also urgently needed. In particular, the well-controlled synthesis of the well-recognized metal–metal nanointer face in a single step remains a key challenge. Here, the synthesis of Cu-supported Ni4Mo nanodots on MoOx nanosheets (Ni4Mo/MoOx) with controllable Ni4Mo particle size and d-band structure is reported via a facile one-step electrodeposition process. Density functional theory (DFT) calculations reveal that the active open-shell effect from Ni-3d-band optimizes the electronic configuration. The Cu-substrate enables the surface Ni–Mo alloy dots to be more electron-rich, forming a local connected electron-rich network, which boosts the charge transfer for effective binding of O-related species and proton–electron charge exchange in the hydrogen evolution reaction. The Cu-supported Ni4Mo/MoOx shows an ultralow overpotential of 16 mV at a current density of 10 mA cm−2 in 1 m KOH, demonstrating the smallest overpotential, at loadings as low as 0.27 mg cm−2, among all non-noble metal catalysts reported to date. Moreover, an overpotential of 105 mV allows it to achieve a current density of 250 mA cm−2 in 70 °C 30% KOH, a remarkable performance for alkaline hydrogen evolution with competitive potential for applications. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Transition metal phosphides (TMPs), albeit promising as hydrogen evolution reaction (HER) catalysts, suffer from the sluggish water dissociation step in alkaline solution, and metal oxides(hydroxides) have been employed to address this problem. However, limited active interface between metal oxides(hydroxides) and phosphides was achieved, leading to unsatisfactory catalytic efficiencies. Therefore, it is still a key challenge to develop a facile way to synthesize the hybrid catalyst of transition metal oxide/phosphide with numerous nanointerfaces. Herein, we report a highly efficient HER catalyst of manganese oxides and cobalt phosphides nanohybrids nanosheets array (denoted as Mn-O@Co-P) with numerous nano-heterointerfaces, facilely grown on carbon cloth (CC) by a simple one-pot process for the first time. The obtained Mn-O@Co-P/CC shows superior activity for HER in alkaline solution with a low overpotential of 96 mV at 10 mA cm-2, a small Tafel slope of 56 mV dec-1 and excellent long-term durability. This work offers a promising one-pot method to synthesize hybrid materials with abundant hetero-nanointerfaces, which is proved to be the powerful strategy for constructing efficient HER catalysts in alkaline solution.

Transition metal phosphides (TMPs), albeit promising as hydrogen evolution reaction (HER) catalysts, suffer from the sluggish water dissociation step in alkaline solution, and metal oxides(hydroxides) have been employed to address this problem. However, limited active interface between metal oxides(hydroxides) and phosphides was achieved, leading to unsatisfactory catalytic efficiencies. Therefore, it is still a key challenge to develop a facile way to synthesize the hybrid catalyst of transition metal oxide/phosphide with numerous nanointerfaces. Herein, we report a highly efficient HER catalyst of manganese oxides and cobalt phosphides nanohybrids nanosheets array (denoted as Mn-O@Co-P) with numerous nano-heterointerfaces, facilely grown on carbon cloth (CC) by a simple one-pot process for the first time. The obtained Mn-O@Co-P/CC shows superior activity for HER in alkaline solution with a low overpotential of 96 mV at 10 mA cm-2, a small Tafel slope of 56 mV dec-1 and excellent long-term durability. This work offers a promising one-pot method to synthesize hybrid materials with abundant hetero-nanointerfaces, which is proved to be the powerful strategy for constructing efficient HER catalysts in alkaline solution.

Currently, in addition to the electroactive non-noble metal water-splitting electrocatalysts, a scalable synthetic route and simple activity enhancement strategy is also urgently needed. In particular, the well-controlled synthesis of the well-recognized metal–metal nanointer face in a single step remains a key challenge. Here, the synthesis of Cu-supported Ni4Mo nanodots on MoOx nanosheets (Ni4Mo/MoOx) with controllable Ni4Mo particle size and d-band structure is reported via a facile one-step electrodeposition process. Density functional theory (DFT) calculations reveal that the active open-shell effect from Ni-3d-band optimizes the electronic configuration. The Cu-substrate enables the surface Ni–Mo alloy dots to be more electron-rich, forming a local connected electron-rich network, which boosts the charge transfer for effective binding of O-related species and proton–electron charge exchange in the hydrogen evolution reaction. The Cu-supported Ni4Mo/MoOx shows an ultralow overpotential of 16 mV at a current density of 10 mA cm−2 in 1 m KOH, demonstrating the smallest overpotential, at loadings as low as 0.27 mg cm−2, among all non-noble metal catalysts reported to date. Moreover, an overpotential of 105 mV allows it to achieve a current density of 250 mA cm−2 in 70 °C 30% KOH, a remarkable performance for alkaline hydrogen evolution with competitive potential for applications. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Despite the many attempts to build ultrathin 2D-2D heterojunctions via wet chemical methods, the resulting composite materials reported to date suffer from poor interfacial bonding and/or complexity of the synthetic protocols. Encouraged by the structural compatibility of Bi2WO6 and Bi2O2S, both of which are 2D semiconductors sharing a rather similar structural unit of a [Bi2O2]2+ slice in their crystal structures, we have successfully fabricated an ultrathin nanosheet with a tightly bonded 2D-2D heterojunction between the two components by facilely joining the [Bi2O2]2+ and [S]2- slices using a simple two-step hydrothermal method. Such a Bi2WO6-Bi2O2S 2D-2D heterojunction has a five-alternating-layer (Bi2O2S-Bi2WO6-Bi2O2S-Bi2WO6-Bi2O2S) sandwich structure and a thickness down to ca. 5 nm and was obtained by simply growing the Bi2O2S layer in situ on the surface of monolayer Bi2WO6 nanosheets. The judicious combination of Bi2WO6 and Bi2O2S through a 2D-2D heterojunction not only extended light absorption in the visible range but also significantly enhanced photo(electro)chemical water splitting efficiencies in comparison to the bare Bi2WO6 nanosheets alone due to the close-bonding-promoted interfacial charge separation. Our findings provide a viable methodology to build a host of nanomaterials with closely bonded 2D nanosheets, which can be used as photocatalysts and electrocatalysts, among others. © 2019 American Chemical Society.

Transition metal phosphides (TMPs), albeit promising as hydrogen evolution reaction (HER) catalysts, suffer from the sluggish water dissociation step in alkaline solution, and metal oxides(hydroxides) have been employed to address this problem. However, limited active interface between metal oxides(hydroxides) and phosphides was achieved, leading to unsatisfactory catalytic efficiencies. Therefore, it is still a key challenge to develop a facile way to synthesize the hybrid catalyst of transition metal oxide/phosphide with numerous nanointerfaces. Herein, we report a highly efficient HER catalyst of manganese oxides and cobalt phosphides nanohybrids nanosheets array (denoted as Mn-O@Co-P) with numerous nano-heterointerfaces, facilely grown on carbon cloth (CC) by a simple one-pot process for the first time. The obtained Mn-O@Co-P/CC shows superior activity for HER in alkaline solution with a low overpotential of 96 mV at 10 mA cm-2, a small Tafel slope of 56 mV dec-1 and excellent long-term durability. This work offers a promising one-pot method to synthesize hybrid materials with abundant hetero-nanointerfaces, which is proved to be the powerful strategy for constructing efficient HER catalysts in alkaline solution.

Currently, in addition to the electroactive non-noble metal water-splitting electrocatalysts, a scalable synthetic route and simple activity enhancement strategy is also urgently needed. In particular, the well-controlled synthesis of the well-recognized metal–metal nanointer face in a single step remains a key challenge. Here, the synthesis of Cu-supported Ni4Mo nanodots on MoOx nanosheets (Ni4Mo/MoOx) with controllable Ni4Mo particle size and d-band structure is reported via a facile one-step electrodeposition process. Density functional theory (DFT) calculations reveal that the active open-shell effect from Ni-3d-band optimizes the electronic configuration. The Cu-substrate enables the surface Ni–Mo alloy dots to be more electron-rich, forming a local connected electron-rich network, which boosts the charge transfer for effective binding of O-related species and proton–electron charge exchange in the hydrogen evolution reaction. The Cu-supported Ni4Mo/MoOx shows an ultralow overpotential of 16 mV at a current density of 10 mA cm−2 in 1 m KOH, demonstrating the smallest overpotential, at loadings as low as 0.27 mg cm−2, among all non-noble metal catalysts reported to date. Moreover, an overpotential of 105 mV allows it to achieve a current density of 250 mA cm−2 in 70 °C 30% KOH, a remarkable performance for alkaline hydrogen evolution with competitive potential for applications. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Despite the many attempts to build ultrathin 2D-2D heterojunctions via wet chemical methods, the resulting composite materials reported to date suffer from poor interfacial bonding and/or complexity of the synthetic protocols. Encouraged by the structural compatibility of Bi2WO6 and Bi2O2S, both of which are 2D semiconductors sharing a rather similar structural unit of a [Bi2O2]2+ slice in their crystal structures, we have successfully fabricated an ultrathin nanosheet with a tightly bonded 2D-2D heterojunction between the two components by facilely joining the [Bi2O2]2+ and [S]2- slices using a simple two-step hydrothermal method. Such a Bi2WO6-Bi2O2S 2D-2D heterojunction has a five-alternating-layer (Bi2O2S-Bi2WO6-Bi2O2S-Bi2WO6-Bi2O2S) sandwich structure and a thickness down to ca. 5 nm and was obtained by simply growing the Bi2O2S layer in situ on the surface of monolayer Bi2WO6 nanosheets. The judicious combination of Bi2WO6 and Bi2O2S through a 2D-2D heterojunction not only extended light absorption in the visible range but also significantly enhanced photo(electro)chemical water splitting efficiencies in comparison to the bare Bi2WO6 nanosheets alone due to the close-bonding-promoted interfacial charge separation. Our findings provide a viable methodology to build a host of nanomaterials with closely bonded 2D nanosheets, which can be used as photocatalysts and electrocatalysts, among others. © 2019 American Chemical Society.

A complete photoelectrochemical (PEC) water splitting system requires a photocathode and a photoanode to host water oxidation and reduction reactions, respectively. It is thus important to search for efficient photoelectrodes capable of full water splitting. Herein, we report on an exploratory study of a new photoelectrode family of ZnxPbOy-ZnPbO3 and Zn2PbO4 similarly synthesized by a simple and economical method and shown to be a promising photocathode (p-type semiconductor) and photoanode (n-type semiconductor), respectively. From PEC measurements, the bare ZnPbO3 photocathode achieved a photocurrent density of -0.94 mA/cm(2) at 0 V versus reversible hydrogen electrode (RHE), whereas the pristine Zn2PbO4 photoanode delivered a photocurrent density of 0.51 mA/cm(2) at 1.23 V versus RHE. By depositing suitable cocatalysts onto the photoelectrodes established above, we also demonstrated unassisted overall PEC water splitting, a rare case, if any, wherein a single material system is compositionally engineered for either of the photoelectrodes.

A complete photoelectrochemical (PEC) water splitting system requires a photocathode and a photoanode to host water oxidation and reduction reactions, respectively. It is thus important to search for efficient photoelectrodes capable of full water splitting. Herein, we report on an exploratory study of a new photoelectrode family of ZnxPbOy-ZnPbO3 and Zn2PbO4 similarly synthesized by a simple and economical method and shown to be a promising photocathode (p-type semiconductor) and photoanode (n-type semiconductor), respectively. From PEC measurements, the bare ZnPbO3 photocathode achieved a photocurrent density of -0.94 mA/cm(2) at 0 V versus reversible hydrogen electrode (RHE), whereas the pristine Zn2PbO4 photoanode delivered a photocurrent density of 0.51 mA/cm(2) at 1.23 V versus RHE. By depositing suitable cocatalysts onto the photoelectrodes established above, we also demonstrated unassisted overall PEC water splitting, a rare case, if any, wherein a single material system is compositionally engineered for either of the photoelectrodes.

A complete photoelectrochemical (PEC) water splitting system requires a photocathode and a photoanode to host water oxidation and reduction reactions, respectively. It is thus important to search for efficient photoelectrodes capable of full water splitting. Herein, we report on an exploratory study of a new photoelectrode family of ZnxPbOy-ZnPbO3 and Zn2PbO4 similarly synthesized by a simple and economical method and shown to be a promising photocathode (p-type semiconductor) and photoanode (n-type semiconductor), respectively. From PEC measurements, the bare ZnPbO3 photocathode achieved a photocurrent density of -0.94 mA/cm(2) at 0 V versus reversible hydrogen electrode (RHE), whereas the pristine Zn2PbO4 photoanode delivered a photocurrent density of 0.51 mA/cm(2) at 1.23 V versus RHE. By depositing suitable cocatalysts onto the photoelectrodes established above, we also demonstrated unassisted overall PEC water splitting, a rare case, if any, wherein a single material system is compositionally engineered for either of the photoelectrodes.

We investigated the adsorption of corannulene (C20H10) on the Ag(111) surface by experimental and simulated scanning tunneling microscopy (STM), X-ray photoemission (XPS) and near-edge X-ray absorption fine structure (NEXAFS). Structural optimizations of the adsorbed molecules were performed by density functional theory (DFT) and the core excited spectra evaluated within the transition potential approach. Corannulene is physisorbed in a bowl-up orientation displaying a very high mobility (diffusing) and dynamics (tilting and spinning) at room temperature. At the monolayer saturation coverage, molecules order into a close compact phase with an average intermolecular spacing of ∼10.5±0.5Å. The lattice mismatch drives a long wavelength structural modulation of the molecular rows, which, however, could not be identified with a specific superlattice periodicity. DFT calculations indicate that the structural and spectroscopic properties are intermediate between those predicted for the limiting cases of an on-hexagon geometry (with a three-fold, ∼8.6Å unit mesh) and an on-pentagon (with a four-fold, ∼11.5Å unit mesh). We suggest that molecules smoothly change their equilibrium configuration along the observed long wavelength modulation of the molecular rows by varying their tilt and azimuth in between the geometric constraints calculated for molecules in the three-fold and four-fold phases

We sample ab initio molecular dynamics trajectories to address the impact of structural fluctuations on elastic lifetimes of adsorbate states at room temperature focusing on heterogeneous charge injection from isonicotinic acid as a key anchoring unit in dyesensitized energy devices. Complementing related theoretical studies, we employ a Green's function technique based on density functional theory to account for a fully semi-infinite substrate of rutile TiO2(110). We explicitly address the effect of a core-excitation, thus enabling the comparison with soft X-ray experiments. We find that taking into account room temperature fluctuations drastically improves the agreement with the experimental lifetime measurements. The presence of a core-hole plays an important role shifting down in energy the spectra and reducing the electron-vibrational coupling of the adsorbate states. This last observation is probably related to the larger localization of the molecular resonance under the presence of a core-hole. The cumulative resonance spectra can be described by Voigt-type profiles obtained by convoluting a Lorentzian peak describing the electronic resonance with a Gaussian distribution modeling the temperature broadening. However, we found that in order to get an optimal description it is crucial to account for the energy dependence of the statistically averaged electronic widths. This energy dependence is dominated by the variation of the density of acceptor states in the substrate.

We sample ab initio molecular dynamics trajectories to address the impact of structural fluctuations on elastic lifetimes of adsorbate states at room temperature focusing on heterogeneous charge injection from isonicotinic acid as a key anchoring unit in dye-sensitized energy devices. Complementing related theoretical studies, we employ a Green's function technique based on density functional theory to account for a fully semi-infinite substrate of rutile TiO(110). We address the effect of a core-excitation enabling direct comparison with soft X-ray experiments. We find that room temperature fluctuations drastically improve the agreement with experimental lifetime measurements while the core-hole plays an important role shifting the spectra and reducing the electron vibrational coupling of the adsorbate states. Ultimately, the emerging resonance spectra highlight the role of the continuum of acceptor states in temperature broadened Voigt-type profiles.

Dynamics of quality attributes derived from Kano model has been recognized as one of the most interesting and fruitful developments of attractive quality theory. The purpose of this study is to propose an integrated method with GM(1,1) model and Markov chain to forecast the dynamics of service quality attributes with limited data and explore the existence of the alternative life cycles. Further, an empirical study of the express delivery industry in China is conducted at four points of time (the year of 2008, 2010, 2012, and 2013) to verify the feasibility of the method. This study not only provides a quantitative method for forecasting the dynamics of service quality attributes with limited information, but also gives evidence for the existence of alternative life cycles of service quality attributes.

Two-dimensional molybdenum sulfide is an attractive noble-metal-free electrocatalyst for the hydrogen evolution reaction (HER). Significant efforts have been made to increase the number of exposed edge sites. However, little attention has been paid to devising edge surface structures of MoS2 sheet stacks to promote the HER kinetics. Herein we report the first demonstration of significantly enhanced HER kinetics by controllably fabricating a stepped MoS2 surface structure. Vertical arrays of MoS2 sheets terminated with such a stepped surface structure have proved to be an outstanding HER electrocatalyst with an overpotential of 104 mV at 10 mA cm(-2), an exchange current density of 0.2 mA cm(-2) and high stability. Experimental and theoretical results indicate that the enhanced electrocatalytic activity of the vertical MoS2 arrays is associated with the unique vertically terminated, highly exposed, stepped surface structure with a nearly thermoneutral H-adsorption energy. This work opens a new avenue to designing and developing layered materials for electrochemical energy applications.

Hydrogen evolution reaction (HER) on earth-abundant molybdenum disulfide (MoS2) in acidic media is a robust process, but is kinetically retarded in alkaline media. Thus, improving the sluggish kinetics for HER in alkaline media is crucial for advancing the performance of water-alkali electrolyzers. Here, we demonstrate a dramatic enhancement of HER kinetics in base by judiciously hybridizing vertical MoS2 sheets with another earth-abundant material, layered double hydroxide (LDH). The resultant MoS2/NiCo-LDH hybrid exhibits an extremely low HER overpotential of 78 mV at 10 mA/cm2 and a low Tafel slope of 76.6 mV/dec in 1 M KOH solution. At the current density of 20 mA/cm2 or even higher, the MoS2/NiCo-LDH composite can operate without degradation for 48 hr. This work not only brought forth a cost-effective and robust electrocatalyst, but more generally opened up new vistas for developing high-performance electrocatalysts in unfavorable media recalcitrant to conventional catalyst design. Central to electrocatalysis are efficient and robust electrocatalysts composed of earth-abundant elements, which are urgently needed for realizing low-cost and high-performance energy conversion devices. Earth-abundant MoS2 has emerged as a promising hydrogen evolution reaction (HER) catalyst with high activity and durability. However, such a high HER performance is only limited to acidic media, the kinetics becoming rather sluggish in alkaline media. Besides the hydrogen (Had) adsorption energy, there should be a second descriptor for gauging the HER catalytic activity in alkaline media, namely the binding of hydroxyl species, because here H has to be discharged from water instead of from hydronium ions in acidic media. This work is the first to successfully design and fabricate a synergistic hybrid catalyst system, which is composed of MoS2 as an H-acceptor and OER-efficient layered double hydroxide as an OH acceptor, for dramatically facilitating the HER process in alkaline media.

Bismuth vanadate (BiVO4) has been regarded as a promising photoanode material for photoelectrochemical (PEC) water splitting owing to its rich elemental abundance and relatively narrow bandgap. However, the incompatibility of the penetration depth and short diffusion length limits its performance. To overcome this shortcoming, we develop a cost-effective stamping method to fabricate inverse nanocone array (ICA) substrates for supporting nanoporous Mo-doped BiVO4 films. The ICAs show a remarkable light trapping effect in such a way that the intensive light absorption region is advantageously shifted from the top of the active layer on a planar substrate to the bottom surrounded by the ICA, where charge separation is strikingly more efficient. By integrating the ICA-photoanode with a tailor-made, bandgap-adjustable perovskite solar cell, we devised a PEC-photovoltaic (PEC-PV) tandem device, which has achieved a self-powered STH efficiency of around 6.3%. Our study opens a new avenue for designing solar fuel devices with PEC-PV architectures.

It is still a challenging issue to design earth-abundant electrocatalysts with low cost, high activity and long-term stability for the hydrogen evolution reaction (HER) based on water splitting in alkaline solutions. Here, we report a facile synthetic route for a three-dimensional, porous Ni/Ni3S2 nano-network on carbon cloth for the efficient catalysis of HER. This unique structure exposes a high proportion of Ni/Ni3S2 hetero-interfaces to the electrolyte, creating a synergetic effect between Ni and Ni3S2 that enhances HER. The synergetic effect at the interface was verified by DFT calculation and involves the interface-assisted heterolytic splitting of H2O into OH− and H+ and the subsequent expeditious H2-forming reaction caused by weakened binding between Ni and H induced by the neighboring Ni3S2. The resulting porous network shows high HER activity in alkaline media, reaching 10 mA cm−2 at 95 mV with a Tafel slope of 66 mV dec−1. This value is much smaller than that of nickel metal, which is currently used in industry.

2D halide perovskite materials have shown great advantages in terms of stability when applied in a photovoltaic device. However, the impediment of charge transport within the layered structure drags down the device performance. Here for the first time, a 3D–2D (MAPbI3-PEA2Pb2I4) graded perovskite interface is demonstrated with synergistic advantages. In addition to the significantly improved ambient stability, this graded combination modifies the interface energy level in such a way that reduces interface charge recombination, leading to an ultrahigh Voc at 1.17 V, a record for NiO-based p-i-n photovoltaic devices. Moreover, benefiting from the graded structure induced continuously upshifts energy level, the photovoltaic device attains a high Jsc of 21.80 mA cm−2 and a high fill factor of 0.78, resulting in an overall power conversion efficiency (PCE) of 19.89%. More importantly, it is showed that such a graded interface structure also suppresses ion migration in the device, accounting for its significantly enhanced thermal stability.

The growing concern about global warming, environmental pollution and energy security has increased the demand for clean energy resources in place of fossil fuel. Cost-efficient generation of hydrogen from water splitting through electrocatalysis holds tremendous promise for clean energy. Central to electrocatalysis are efficient and robust electrocatalysts composed of earth-abundant elements, which are urgently needed for realizing low-cost and high-performance energy conversion devices. Transition metal compounds (TMCs) are a group of attractive noble-metal-free electrocatalysts for the hydrogen evolution reaction (HER). The incorporation of foreign nonmetal atoms into TMCs is a way of controllable disorder engineering and modification of their electronic structure, and thus may realize the synergistic modulations of both activity and conductivity for efficient HER performance. In the last few years, the interest in binary-nonmetal TMCs as an efficient HER electrocatalyst has grown exponentially owing to their fascinating electronic structure and chemical properties. Here, we sum up the recent developments of binary-nonmetal TMCs in HER electrocatalysis from the viewpoint of their tunable physicochemical properties. In addition, we identify major challenges ahead in this area and refine viable strategies and future research directions that will effectively address the said challenges.

Hydrogen evolution reaction (HER) on earth-abundant molybdenum disulfide (MoS2) in acidic media is a robust process, but is kinetically retarded in alkaline media. Thus, improving the sluggish kinetics for HER in alkaline media is crucial for advancing the performance of water-alkali electrolyzers. Here, we demonstrate a dramatic enhancement of HER kinetics in base by judiciously hybridizing vertical MoS2 sheets with another earth-abundant material, layered double hydroxide (LDH). The resultant MoS2/NiCo-LDH hybrid exhibits an extremely low HER overpotential of 78 mV at 10 mA/cm2 and a low Tafel slope of 76.6 mV/dec in 1 M KOH solution. At the current density of 20 mA/cm2 or even higher, the MoS2/NiCo-LDH composite can operate without degradation for 48 hr. This work not only brought forth a cost-effective and robust electrocatalyst, but more generally opened up new vistas for developing high-performance electrocatalysts in unfavorable media recalcitrant to conventional catalyst design. Central to electrocatalysis are efficient and robust electrocatalysts composed of earth-abundant elements, which are urgently needed for realizing low-cost and high-performance energy conversion devices. Earth-abundant MoS2 has emerged as a promising hydrogen evolution reaction (HER) catalyst with high activity and durability. However, such a high HER performance is only limited to acidic media, the kinetics becoming rather sluggish in alkaline media. Besides the hydrogen (Had) adsorption energy, there should be a second descriptor for gauging the HER catalytic activity in alkaline media, namely the binding of hydroxyl species, because here H has to be discharged from water instead of from hydronium ions in acidic media. This work is the first to successfully design and fabricate a synergistic hybrid catalyst system, which is composed of MoS2 as an H-acceptor and OER-efficient layered double hydroxide as an OH acceptor, for dramatically facilitating the HER process in alkaline media.

Bismuth vanadate (BiVO4) has been regarded as a promising photoanode material for photoelectrochemical (PEC) water splitting owing to its rich elemental abundance and relatively narrow bandgap. However, the incompatibility of the penetration depth and short diffusion length limits its performance. To overcome this shortcoming, we develop a cost-effective stamping method to fabricate inverse nanocone array (ICA) substrates for supporting nanoporous Mo-doped BiVO4 films. The ICAs show a remarkable light trapping effect in such a way that the intensive light absorption region is advantageously shifted from the top of the active layer on a planar substrate to the bottom surrounded by the ICA, where charge separation is strikingly more efficient. By integrating the ICA-photoanode with a tailor-made, bandgap-adjustable perovskite solar cell, we devised a PEC-photovoltaic (PEC-PV) tandem device, which has achieved a self-powered STH efficiency of around 6.3%. Our study opens a new avenue for designing solar fuel devices with PEC-PV architectures.

2D halide perovskite materials have shown great advantages in terms of stability when applied in a photovoltaic device. However, the impediment of charge transport within the layered structure drags down the device performance. Here for the first time, a 3D–2D (MAPbI3-PEA2Pb2I4) graded perovskite interface is demonstrated with synergistic advantages. In addition to the significantly improved ambient stability, this graded combination modifies the interface energy level in such a way that reduces interface charge recombination, leading to an ultrahigh Voc at 1.17 V, a record for NiO-based p-i-n photovoltaic devices. Moreover, benefiting from the graded structure induced continuously upshifts energy level, the photovoltaic device attains a high Jsc of 21.80 mA cm−2 and a high fill factor of 0.78, resulting in an overall power conversion efficiency (PCE) of 19.89%. More importantly, it is showed that such a graded interface structure also suppresses ion migration in the device, accounting for its significantly enhanced thermal stability.

The growing concern about global warming, environmental pollution and energy security has increased the demand for clean energy resources in place of fossil fuel. Cost-efficient generation of hydrogen from water splitting through electrocatalysis holds tremendous promise for clean energy. Central to electrocatalysis are efficient and robust electrocatalysts composed of earth-abundant elements, which are urgently needed for realizing low-cost and high-performance energy conversion devices. Transition metal compounds (TMCs) are a group of attractive noble-metal-free electrocatalysts for the hydrogen evolution reaction (HER). The incorporation of foreign nonmetal atoms into TMCs is a way of controllable disorder engineering and modification of their electronic structure, and thus may realize the synergistic modulations of both activity and conductivity for efficient HER performance. In the last few years, the interest in binary-nonmetal TMCs as an efficient HER electrocatalyst has grown exponentially owing to their fascinating electronic structure and chemical properties. Here, we sum up the recent developments of binary-nonmetal TMCs in HER electrocatalysis from the viewpoint of their tunable physicochemical properties. In addition, we identify major challenges ahead in this area and refine viable strategies and future research directions that will effectively address the said challenges.

It is still a challenging issue to design earth-abundant electrocatalysts with low cost, high activity and long-term stability for the hydrogen evolution reaction (HER) based on water splitting in alkaline solutions. Here, we report a facile synthetic route for a three-dimensional, porous Ni/Ni3S2 nano-network on carbon cloth for the efficient catalysis of HER. This unique structure exposes a high proportion of Ni/Ni3S2 hetero-interfaces to the electrolyte, creating a synergetic effect between Ni and Ni3S2 that enhances HER. The synergetic effect at the interface was verified by DFT calculation and involves the interface-assisted heterolytic splitting of H2O into OH− and H+ and the subsequent expeditious H2-forming reaction caused by weakened binding between Ni and H induced by the neighboring Ni3S2. The resulting porous network shows high HER activity in alkaline media, reaching 10 mA cm−2 at 95 mV with a Tafel slope of 66 mV dec−1. This value is much smaller than that of nickel metal, which is currently used in industry.

Two-dimensional molybdenum sulfide is an attractive noble-metal-free electrocatalyst for the hydrogen evolution reaction (HER). Significant efforts have been made to increase the number of exposed edge sites. However, little attention has been paid to devising edge surface structures of MoS2 sheet stacks to promote the HER kinetics. Herein we report the first demonstration of significantly enhanced HER kinetics by controllably fabricating a stepped MoS2 surface structure. Vertical arrays of MoS2 sheets terminated with such a stepped surface structure have proved to be an outstanding HER electrocatalyst with an overpotential of 104 mV at 10 mA cm(-2), an exchange current density of 0.2 mA cm(-2) and high stability. Experimental and theoretical results indicate that the enhanced electrocatalytic activity of the vertical MoS2 arrays is associated with the unique vertically terminated, highly exposed, stepped surface structure with a nearly thermoneutral H-adsorption energy. This work opens a new avenue to designing and developing layered materials for electrochemical energy applications.

The functional application of metallic glasses in the catalytic field has widely attracted research attention due to its unique atomic structure compared to crystalline materials. It has been reported that metallic glasses can effectively activate H2O2 and persulfate, yet the activation of peroxymonosulfate by metallic glasses is not studied well. In this work, the metallic glass with atomic composition of Fe78Si9B13 was applied for investigating the peroxymonosulfate (PMS) activation on degradation of naphthol green B (NGB) dye. The change of surface morphology indicated the important role of oxide films during the dye degradation. The effects and first-order kinetics model of various reaction parameters were evaluated systematically, including PMS concentration, catalyst dosage, irradiation intensity, and dye concentration. The results showed that about 98% of the dye removal rate could be achieved only within 10 min under rational conditions. The reaction kinetics k of 0.1339 min−1 without ribbons was sharply improved to 0.3140 min−1 by adding 0.5 g/L ribbons, indicating the superior activation ability of Fe78Si9B13 metallic glass. The recycling experiment revealed that the Fe78Si9B13 ribbons exhibited the excellent surface stability and catalytic reusability for activating PMS even after reused for 10th run.

The functional application of metallic glasses in the catalytic field has widely attracted research attention due to its unique atomic structure compared to crystalline materials. It has been reported that metallic glasses can effectively activate H2O2 and persulfate, yet the activation of peroxymonosulfate by metallic glasses is not studied well. In this work, the metallic glass with atomic composition of Fe78Si9B13 was applied for investigating the peroxymonosulfate (PMS) activation on degradation of naphthol green B (NGB) dye. The change of surface morphology indicated the important role of oxide films during the dye degradation. The effects and first-order kinetics model of various reaction parameters were evaluated systematically, including PMS concentration, catalyst dosage, irradiation intensity, and dye concentration. The results showed that about 98 % of the dye removal rate could be achieved only within 10 min under rational conditions. The reaction kinetics k of 0.1339 min−1 without ribbons was sharply improved to 0.3140 min−1 by adding 0.5 g/L ribbons, indicating the superior activation ability of Fe78Si9B13 metallic glass. The recycling experiment revealed that the Fe78Si9B13 ribbons exhibited the excellent surface stability and catalytic reusability for activating PMS even after reused for 10th run.

Hydrogen evolution reaction (HER) on earth-abundant molybdenum disulfide (MoS2) in acidic media is a robust process, but is kinetically retarded in alkaline media. Thus, improving the sluggish kinetics for HER in alkaline media is crucial for advancing the performance of water-alkali electrolyzers. Here, we demonstrate a dramatic enhancement of HER kinetics in base by judiciously hybridizing vertical MoS2 sheets with another earth-abundant material, layered double hydroxide (LDH). The resultant MoS2/NiCo-LDH hybrid exhibits an extremely low HER overpotential of 78 mV at 10 mA/cm2 and a low Tafel slope of 76.6 mV/dec in 1 M KOH solution. At the current density of 20 mA/cm2 or even higher, the MoS2/NiCo-LDH composite can operate without degradation for 48 hr. This work not only brought forth a cost-effective and robust electrocatalyst, but more generally opened up new vistas for developing high-performance electrocatalysts in unfavorable media recalcitrant to conventional catalyst design. Central to electrocatalysis are efficient and robust electrocatalysts composed of earth-abundant elements, which are urgently needed for realizing low-cost and high-performance energy conversion devices. Earth-abundant MoS2 has emerged as a promising hydrogen evolution reaction (HER) catalyst with high activity and durability. However, such a high HER performance is only limited to acidic media, the kinetics becoming rather sluggish in alkaline media. Besides the hydrogen (Had) adsorption energy, there should be a second descriptor for gauging the HER catalytic activity in alkaline media, namely the binding of hydroxyl species, because here H has to be discharged from water instead of from hydronium ions in acidic media. This work is the first to successfully design and fabricate a synergistic hybrid catalyst system, which is composed of MoS2 as an H-acceptor and OER-efficient layered double hydroxide as an OH acceptor, for dramatically facilitating the HER process in alkaline media.

2D halide perovskite materials have shown great advantages in terms of stability when applied in a photovoltaic device. However, the impediment of charge transport within the layered structure drags down the device performance. Here for the first time, a 3D–2D (MAPbI3-PEA2Pb2I4) graded perovskite interface is demonstrated with synergistic advantages. In addition to the significantly improved ambient stability, this graded combination modifies the interface energy level in such a way that reduces interface charge recombination, leading to an ultrahigh Voc at 1.17 V, a record for NiO-based p-i-n photovoltaic devices. Moreover, benefiting from the graded structure induced continuously upshifts energy level, the photovoltaic device attains a high Jsc of 21.80 mA cm−2 and a high fill factor of 0.78, resulting in an overall power conversion efficiency (PCE) of 19.89%. More importantly, it is showed that such a graded interface structure also suppresses ion migration in the device, accounting for its significantly enhanced thermal stability.

Bismuth vanadate (BiVO4) has been regarded as a promising photoanode material for photoelectrochemical (PEC) water splitting owing to its rich elemental abundance and relatively narrow bandgap. However, the incompatibility of the penetration depth and short diffusion length limits its performance. To overcome this shortcoming, we develop a cost-effective stamping method to fabricate inverse nanocone array (ICA) substrates for supporting nanoporous Mo-doped BiVO4 films. The ICAs show a remarkable light trapping effect in such a way that the intensive light absorption region is advantageously shifted from the top of the active layer on a planar substrate to the bottom surrounded by the ICA, where charge separation is strikingly more efficient. By integrating the ICA-photoanode with a tailor-made, bandgap-adjustable perovskite solar cell, we devised a PEC-photovoltaic (PEC-PV) tandem device, which has achieved a self-powered STH efficiency of around 6.3%. Our study opens a new avenue for designing solar fuel devices with PEC-PV architectures.