Neighbouring Synergy in High-Density Single Ir Atoms on CoGaOOH for Efficient Alkaline Electrocatalytic Oxygen Evolution.

The catalytic performance of single-atom catalysts was strictly limited by isolated single-atom sites. Fabricating high-density single atoms to realize the synergetic interaction in neighbouring single atoms could optimize the adsorption behaviors of reaction intermediates, which exhibited great potential to break performance limitations and deepen mechanistic understanding of electrocatalysis. However, the catalytic behavior governed by neighbouring single atoms is particularly elusive and has yet to be understood. Herein, we revealed that the synergetic interaction in neighbouring single atoms contributes to superior performance for oxygen evolution relative to isolated Ir single atoms. Neighbouring single atoms was achieved by fabricating high-density single atoms to narrow the distance between single atoms. Electrochemical measurements demonstrated that the Nei-Ir1/CoGaOOH with neighbouring Ir single atoms exhibited a low overpotential of 170 mV at a current density of 10 mA cm-2, and long-durable stability over 2000 h for oxygen evolution. Mechanistic studies revealed that neighbouring single atoms synergetic stabilized the *OOH intermediates via extra hydrogen bonding interactions, thus significantly reducing the reaction energy barriers, as compared to isolated Ir single atoms. The discovery of the synergetic interaction in neighbouring single atoms could offer guidance for the development of efficient electrocatalysts, thus accelerating the world's transition to sustainable energy.

Bipyridine-Confined Silver Single-Atom Catalysts Facilitate In-Plane C-O Coupling for Propylene Electrooxidation.

The electrooxidation of propylene presents a promising route for the production of 1,2-propylene glycol (PG) under ambient conditions. However, the C-O coupling process remains a challenge owing to the high energy barrier. In this work, we developed a highly efficient electrocatalyst of bipyridine-confined Ag single atoms on UiO-bpy substrates (Ag SAs/UiO-bpy), which exposed two in-plane coordination vacancies during reaction for the co-adsorption of key intermediates. Detailed structure and electronic property analyses demonstrate that CH3CHCH2OH* and *OH could stably co-adsorb in a square planar configuration, which then accelerates the charge transfer between them. The combination of stable co-adsorption and efficient charge transfer facilitates the C-O coupling process, thus significantly lowering its energy barrier. At 2.4 V versus a reversible hydrogen electrode, Ag SAs/UiO-bpy achieved a record-high activity of 61.9 gPG m-2 h-1. Our work not only presents a robust electrocatalyst but also advances a new perspective on catalyst design for propylene electrooxidation.

Site-specific metal-support interaction to switch the activity of Ir single atoms for oxygen evolution reaction.

The metal-support interactions (MSI) could greatly determine the electronic properties of single-atom catalysts, thus affecting the catalytic performance. However, the typical approach to regulating MSI usually suffers from interference of the variation of supports or sacrificing the stability of catalysts. Here, we effectively regulate the site-specific MSI of Ir single atoms anchored on Ni layered double hydroxide through an electrochemical deposition strategy. Cathodic deposition drives Ir atoms to locate at three-fold facial center cubic hollow sites with strong MSI, while anodic deposition drives Ir atoms to deposit onto oxygen vacancy sites with weak MSI. The mass activity and intrinsic activity of Ir single-atom catalysts with strong MSI towards oxygen evolution reaction are 19.5 and 5.2 times that with weak MSI, respectively. Mechanism study reveals that the strong MSI between Ir atoms and the support stimulates the activity of Ir sites by inducing the switch of active sites from Ni sites to Ir sites and optimizes the adsorption strength of intermediates, thereby enhancing the activity.

Pore Structure and Fractal Characteristics of Tight Sandstones Based on Nuclear Magnetic Resonance: A Case Study in the Triassic Yanchang Formation of the Ordos Basin, China.

The characterization of the pore structure of tight sandstones is of great importance for the exploration and development of tight oil reservoirs. However, little attention has been given to the geometrical features of pores with various scales, which implies that the effect of pores on the fluid flow and storage capacity is still ambiguous and presents a significant challenge to the risk assessment of tight oil reservoirs. This study investigates the pore structure characteristics of tight sandstones by applying thin section petrography, scanning electron microscopy, nuclear magnetic resonance, fractal theory, and geometric analysis. The results indicate that the tight sandstones have a binary pore system, consisting of small pores and combine pores. A shuttlecock model expresses the shape of the small pore. The radius of the small pore is comparable to the throat radius, and the connectivity of the small pore is poor. A spiny spherical model describes the shape of the combine pore. The connectivity of the combine pore is good, and the pore radius is larger than the throat radius. The most significant contribution to the storage space of the tight sandstones is attributed to the small pores, while permeability is primarily controlled by the combine pores. The heterogeneity of the combine pore has a strong positive correlation with flow capacity, which is associated with the multiple throats of the combine pores that developed during diagenesis. Therefore, the sandstones that are dominated by combine pores and are located near the source rocks represent the most favorable area for the exploitation and development of tight sandstone reservoirs.

Remote Synergy between Heterogeneous Single Atoms and Clusters for Enhanced Oxygen Evolution.

Integrating single atoms and clusters into one system is a novel strategy to achieve desired catalytic performances. Compared with homogeneous single-atom cluster catalysts, heterogeneous ones combine the merits of different species and therefore show greater potential. However, it is still challenging to construct single-atom cluster systems of heterogeneous species, and the underlying mechanism for activity improvement remains unclear. In this work, we developed a heterogeneous single-atom cluster catalyst (ConIr1/N-C) for efficient oxygen evolution. The Ir single atoms worked in synergy with the Co clusters at a distance of about 8 Å, which optimized the configuration of the key intermediates. Consequently, the oxygen evolution activity was significantly improved on ConIr1/N-C relative to the Co cluster catalyst (Con/N-C), exhibiting an overpotential lower by 107 mV than that of Con/N-C at 10 mA cm-2 and a turnover frequency 50.9 times as much as that of Con/N-C at an overpotential of 300 mV.

Dynamically Reversible Interconversion of Molecular Catalysts for Efficient Electrooxidation of Propylene into Propylene Glycol.

For the electrooxidation of propylene into 1,2-propylene glycol (PG), the process involves two key steps of the generation of *OH and the transfer of *OH to the C═C bond in propylene. The strong *OH binding energy (EB(*OH)) favors the dissociation of H2O into *OH, whereas the transfer of *OH to propylene will be impeded. The scaling relationship of the EB(*OH) plays a key role in affecting the catalytic performance toward propylene electrooxidation. Herein, we adopt an immobilized Ag pyrazole molecular catalyst (denoted as AgPz) as the electrocatalyst. The pyrrolic N-H in AgPz could undergo deprotonation to form pyrrolic N (denoted as AgPz-Hvac), which can be protonated reversibly. During propylene electrooxidation, the strong EB(*OH) on AgPz favors the dissociation of H2O into *OH. Subsequently, the AgPz transforms into AgPz-Hvac that possesses weak EB(*OH), benefiting to the further combination of *OH and propylene. The dynamically reversible interconversion between AgPz and AgPz-Hvac accompanied by changeable EB(*OH) breaks the scaling relationship, thus greatly lowering the reaction barrier. At 2.0 V versus Ag/AgCl electrode, AgPz achieves a remarkable yield rate of 288.9 mmolPG gcat-1 h-1, which is more than one order of magnitude higher than the highest value ever reported.

Boosting Electrical Response toward Trace Volatile Organic Compounds Molecules via Pulsed Temperature Modulation of Pt Anchored WO3 Chemiresistor.

Insufficient limit of detection (LoD) toward volatile organic compounds (VOCs) hinders the promising applications of metal oxide chemiresistors in emerging air quality monitoring and/or breath analysis. There is an inherent limitation of widely adopted strategies of creating sensitive chemiresistors then operating at the optimized temperature via a continuous heating (CH) mode. Herein, a strategy combining Pt single atoms anchoring (chemical sensitization) with pulsed temperature modulation (PTM, physical sensitization) is proposed. Apart from generating abundant surface asymmetric oxygen vacancy (Pt-VO -W) active sites at pulsed high temperature (HT) stage, inward diffusion of trace target VOCs across the sensing layer at pulsed low temperature stage (driven by PTM induced concentration gradient), can greatly enhance the charge interaction probability between the generated surface active species and the surrounding VOCs, and thus offers a novel avenue on addressing the bottleneck issue of low LoD by PTM. Triggered by HT of 300 °C, the responses of Pt anchored WO3 chemiresistor to 1 ppm trimethylamine (TMA) and xylene can be drastically boosted from 1.9 (CH) to 6541.5 (PTM) and 1.5 (CH) to 1001.1 (PTM), respectively. And ultra-low theoretic LoD of 0.78 ppt (TMA) and 0.18 ppt (xylene) are successfully achieved, respectively.

Tuning the Electronic and Steric Interaction at the Atomic Interface for Enhanced Oxygen Evolution.

The two-dimensional surface or one-dimensional interface of heterogeneous catalysts is essential to determine the adsorption strengths and configurations of the reaction intermediates for desired activities. Recently, the development of single-atom catalysts has enabled an atomic-level understanding of catalytic processes. However, it remains obscure whether the conventional concept and mechanism of one-dimensional interface are applicable to zero-dimensional single atoms. In this work, we arranged the locations of single atoms to explore their interfacial interactions for improved oxygen evolution. When iridium single atoms were confined into the lattice of CoOOH, efficient electron transfer between Ir and Co tuned the adsorption strength of oxygenated intermediates. In contrast, atomic iridium species anchored on the surface of CoOOH induced inappreciable modification in electronic structures, whereas steric interactions with key intermediates at its Ir-OH-Co interface played a primary role in reducing its energy barrier toward oxygen evolution.

Selectively anchoring single atoms on specific sites of supports for improved oxygen evolution.

The homogeneity of single-atom catalysts is only to the first-order approximation when all isolated metal centers interact identically with the support. Since the realistic support with various topologies or defects offers diverse coordination environments, realizing real homogeneity requires precise control over the anchoring sites. In this work, we selectively anchor Ir single atoms onto the three-fold hollow sites (Ir1/TO-CoOOH) and oxygen vacancies (Ir1/VO-CoOOH) on defective CoOOH surface to investigate how the anchoring sites modulate catalytic performance. The oxygen evolution activities of Ir1/TO-CoOOH and Ir1/VO-CoOOH are improved relative to CoOOH through different mechanisms. For Ir1/TO-CoOOH, the strong electronic interaction between single-atom Ir and the support modifies the electronic structure of the active center for stronger electronic affinity to intermediates. For Ir1/VO-CoOOH, a hydrogen bonding is formed between the coordinated oxygen of single-atom Ir center and the oxygenated intermediates, which stabilizes the intermediates and lowers the energy barrier of the rate-determining step.