Nanoscale hetero-interfaces for electrocatalytic and photocatalytic water splitting

As green and sustainable methods to produce hydrogen energy, photocatalytic and electrochemical water splitting have been widely studied. In order to find efficient photocatalysts and electrocatalysts, materials with various composition, size, and surface/interface are investigated. In recent years, constructing suitable nanoscale hetero-interfaces can not only overcome the disadvantages of the single-phase material, but also possibly provide new functionalities. In this review, we systematically introduce the fundamental understanding and experimental progress in nanoscale hetero-interface engineering to design and fabricate photocatalytic and electrocatalytic materials for water splitting. The basic principles of photo-/electro-catalytic water splitting and the fundamentals of nanoscale hetero-interfaces are briefly introduced. The intrinsic behaviors of nanoscale hetero-interfaces on electrocatalysts and photocatalysts are summarized, which are the electronic structure modulation, space charge separation, charge/electron/mass transfer, support effect, defect effect, and synergistic effect. By highlighting the main characteristics of hetero-interfaces, the main roles of hetero-interfaces for electrocatalytic and photocatalytic water splitting are discussed, including excellent electronic structure, efficient charge separation, lower reaction energy barriers, faster charge/electron/mass transfer, more active sites, higher conductivity, and higher stability on hetero-interfaces. Following above analysis, the developments of electrocatalysts and photocatalysts with hetero-structures are systematically reviewed.

Opportunity of Atomically Thin Two-Dimensional Catalysts for Promoting CO2 Electroreduction

ConspectusExcessive use of fossil fuels has not only led to energy shortage but also caused serious environmental pollution problems due to the massive emissions of industrial waste gas. As the main component of industrial waste gas, CO₂ molecules can also be utilized as an important raw material for renewable fuels. Thus, the effective capture and conversion of CO₂ has been considered one of the best potential strategies to mitigate the energy crisis and lower the greenhouse effect simultaneously.In this case, CO₂ electroreduction to high-value-added chemicals provides an available approach to accomplish this important goal. Nonetheless, the CO₂ molecule is extremely stable with a high dissociation energy. With regard to the traditional electrocatalytic systems, there are three main factors that hinder their practical applications: (i) sluggish carrier transport dynamics; (ii) high energy barrier for CO₂ activation; (iii) poor product selectivity. Therefore, solving these three crucial problems is the key to the development of efficient electrocatalytic CO₂ reduction systems.Considering that the CO₂ molecule is a typical Lewis acid with a high first ionization energy and electronic affinity, electron-rich catalysts could help to activate the CO₂ molecule and improve the conversion efficiency. In view of this, atomically thin two-dimensional electrocatalysts, benefiting from their significantly increased density of states near the Fermi level, have great potential to effectively accelerate the dynamics of electron transport. Moreover, their high fraction of surface active sites and enhanced local charge density could remarkably reduce the energy barrier for CO₂ activation. Furthermore, their modulated electronic structure could alter the catalytic reaction pathway and improve the product selectivity. Meanwhile, the concise two-dimensional configuration facilitates in situ characterization as well as the establishment and simulation of theoretical models, which helps to reveal the mechanism of electrocatalytic CO₂ reduction, thereby speeding up the development of CO₂ conversion technology.In this Account, we summarize recent progress in tailoring the electronic structure of atomically thin two-dimensional electrocatalysts by different methods. Meanwhile, we highlight the structure-property relationship between the electronic structure regulation and the catalytic activity/product selectivity of atomically thin two-dimensional electrocatalysts, and discuss the underlying fundamental mechanism with the aid of in situ characterization techniques. Finally, we discuss the major challenges and opportunities for the future development of CO₂ electroreduction. It is expected that this Account will help researchers to better understand CO₂ electroreduction and guide better design of high-performance electrocatalytic systems.

Mechanistic insight into H2-mediated Ni surface diffusion and deposition to form branched Ni nanocrystals: a theoretical study

Present work systematically investigates the kinetic role played by H2 molecules during Ni surface diffusion and deposition to generate branched Ni nanostructures by employing Density Functional Theory (DFT) calculations and ab initio molecule dynamic (AIMD) simulations, respectively. The Ni surface diffusion results unravel that in comparison to the scenarios of Ni(110) and Ni(100), both the subsurface and surface H hinder the Ni surface diffusion over Ni(111) especially under the surface H coverage of 1.5 ML displaying the lowest Ds values, which greatly favors the trapping of the adatom Ni and subsequent overgrowth along the 111 direction. The Ni deposition simulations by AIMD further suggest that both the H2 molecule (in solution) and surface dissociatively adsorbed atomic H can promote Ni depositions onto Ni(111) and Ni(110) facets in a liquid solution. Moreover, a cooperation effect between H2 molecules and surface atomic H can be clearly observed, which greatly favors Ni depositions. Additionally, in addition to working as the solvent, the liquid C2H5OH can also interact with the Ni(111) surface to produce the surface atomic H, which then favored the Ni deposition. Finally, the Ni deposition rate predicted using the deposition constant (Ddep) was found to be much higher than its surface diffusion rate predicted using Ds for Ni(111) and Ni(110), which quantitatively verified the overgrowth along the 111 and 110 directions to produce the branched Ni nanostructures.

Quasi Optical Cavity of Hierarchical ZnO Nanosheets@Ag Nanoravines with Synergy of Near- and Far-Field Effects for in Situ Raman Detection

The vertically interlaced hierarchical structure (HS) of ZnO nanosheets (NSs)@Ag nanoravines (NRs) as a quasi optical cavity (QOC) for Raman enhancement has been studied experimentally and theoretically in this work. A novel synergism of near- and far-field effects of Ag NRs is facilitated by the multiple oscillation of light inside the ZnO QOC, providing wide distributions of "hot spots" in a large space. The "spatial hot spots" in the HS bring reliable signal collection in in situ Raman detection. Without any specific materials and methods adopted, this HS provides researchers a new way to adjust the light in the fields of Raman enhancement.

An Fe-doped NiV LDH ultrathin nanosheet as a highly efficient electrocatalyst for efficient water oxidation

An Fe-doped NiV LDH ultrathin nanosheet was fabricated as a highly efficient electrocatalyst for efficient water oxidation.