Photocatalytic CO 2 conversion to CO is currently attracting a lot of attention as an environmentally benign strategy for curbing anthropogenic CO 2 emissions while delivering commodity chemicals. [1] An ideal CO 2 reduction photocatalyst would have a low energy barrier pathway for CO 2 reduction and be highly selective in terms of the product generated. To date, photocatalytic CO 2 reduction remains inefficient and the rates low, which is explained by the chemical stability of CO 2 molecule and the competing water splitting reaction which lowers product selectivity. [2] Considerable research effort is currently being directed toward improving photocatalytic CO 2 reduction kinetics and also tailoring the product distribution of the reaction. However, the simultaneous enhancement of CO 2 photoreduction activity and product selectivity is very challenging. [3] Owing to the maximal active metal utilization, accessibility of active sites and unique catalytic properties, metal singleatom catalysts (SACs) hold great potential in high performance photocatalyst fabrication. [4,5] Immobilization of Co, Fe, Cu, Mn, or Re atoms in zeolites, MOFs, COFs, and lamellar materials (g-C 3 N 4 , graphdiyne) has resulted in a number of catalyst/ photocatalyst systems with highly efficiency/selectivity for photocatalytic CO 2 reduction. [6] However, due to the fact that these single metal atoms are often coordinated by N/C matrix (M-C/N unit), extensive sacrificial agents are often required to achieve stability. [6a,6b] Further, a number of the supports used to date in SAC fabrication such as zeolites, MOFs, and COFs are poor light-absorbers and/or electron-conductors, necessitating the use of photosensitizers as electron donors. [6d] These bottlenecks impair the application of SACs in photocatalytic CO 2 reduction, forcing a rethink in the design and materials used in SAC construction. Recently, a photocatalyst system comprising Co SACs supported by Bi 3 O 4 Br was reported, [7] in which the Co atoms occupied oxygen vacancy sites in Bi 3 O 4 Br. The photocatalyst system offers efficient CO 2 to CO conversion without the need for any sacrificial agents/photosensitizers, representing a major breakthrough in CO 2 reduction reaction (CRR) photocatalyst development. Our previous work has demonstrated that Ni SACs were more active than Co SACs for CO 2 reduction to CO, [8] suggesting that further improvements in photocatalytic performance should be possible by substituting Co for Ni.

The development of efficient and stable electrocatalysts for the oxygen reduction reaction (ORR) is critical for the large-scale production of fuel cells. Platinum (Pt) nanoparticle catalysts show excellent performance for ORR, though the high cost of Pt is al imiting factor that directly impacts fuel cell production costs. Alloying Pt with other transition metals is an effective strategy to reduce Pt utilization whilst maintaining good ORR performance. In this work, novel hollow PtFe alloy catalysts were successfully synthesized by high-temperature pyrolysis of SiO 2 -coated Pt-Fe 3 O 4 nanoparticle dimers supported on carbon at 900 8C, followed by SiO 2 shell removal and partial dealloying of the PtFe nanoparticles formed using HF.T he obtained hollow PtFe nanoparticle catalysts (denoted herein as PtFe-900) showed a2 .3-fold enhancement in ORR mass activity compared to PtFe nanoparticles synthesized without SiO 2 protection,a nd ar emarkable 7.8-fold enhancement relative to ac ommercial Pt/C catalyst. Further,a fter 10 000 potential cycles, the ORR mass activity of PtFe-900r emained very high (90.9 %o ft he initial mass activity). The outstanding ORR performance of PtFe-900c an be attributed to the modification of Pt lattice and electronic structure by alloying with Fe at high temperature under the protection of the SiO 2 coating. This work guides the development of improved, highly dispersed Ptbased alloy nanoparticle catalysts for ORR and fuel cell applications.

The large‐scale application of proton exchange membrane fuel cells is currently hampered by high cost of commercial Pt catalysts and their susceptibility to poisoning by CO impurities in H2 feed. In this context, the development of CO‐tolerant electrocatalysts with high Pt atom utilization efficiency for hydrogen oxidation reaction (HOR) is of critical importance. Herein, Pt single atoms are successfully immobilized on chromium nitride nanoparticles by atomic layer deposition method, denoted as Pt SACs/CrN. Electrochemical tests establish Pt SACs/CrN to be a very efficient HOR catalyst, with a mass activity that is 5.7 times higher than commercial PtRu/C. Strikingly, the excellent performance of Pt SACs/CrN is maintained after introducing 1000 ppm of CO in H2 feed. The excellent CO‐tolerance of Pt SACs/CrN is related to weaker CO adsorption on Pt single atoms. This work provides guidelines for the design and construction of active and CO‐tolerant catalysts for HOR.

Based on the basic principle of the porosity method in image segmentation, considering the relationship between the porosity of the rocks and the fractal characteristics of the pore structures, a new improved image segmentation method was proposed, which uses the calculated porosity of the core images as a constraint to obtain the best threshold. The results of comparative analysis show that the porosity method can best segment images theoretically, but the actual segmentation effect is deviated from the real situation. Due to the existence of heterogeneity and isolated pores of cores, the porosity method that takes the experimental porosity of the whole core as the criterion cannot achieve the desired segmentation effect. On the contrary, the new improved method overcomes the shortcomings of the porosity method, and makes a more reasonable binary segmentation for the core grayscale images, which segments images based on the actual porosity of each image by calculated. Moreover, the image segmentation method based on the calculated porosity rather than the measured porosity also greatly saves manpower and material resources, especially for tight rocks.

Developing efficient and stable Pt‐based oxygen reduction reaction (ORR) catalysts is a way to promote the large‐scale application of fuel cells. Pt‐based alloy nanowires are promising ORR catalysts, but their application is hampered by activity loss caused by structural destruction during long‐term cycling. Herein, the preparation of ordered PtFeIr intermetallic nanowire catalysts with an average diameter of 2.6 nm and face‐centered tetragonal structure (fct‐PtFeIr/C) is reported. A silica‐protected strategy prevents the deformation of PtFeIr nanowires during the phase transition at high temperature. The as‐prepared fct‐PtFeIr/C exhibited superior mass activity for ORR (2.03 A mgPt−1) than disordered PtFeIr nanowires with face‐centered cubic structure (1.11 A mgPt−1) and commercial Pt/C (0.21 A mgPt−1). Importantly, the structure and electrochemical performance of fct‐PtFeIr/C were maintained after stability tests, showing the advantages of the ordered structure.

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Based on the results of rate-controlled mercury-injection experiments, the microscopic pore-throat structure characteristics of tight sandstone in Sha-1 Section and tight limestone in Da’anzhai Section of Sichuan Basin were quantitatively characterized. The results show that the pore radius distribution characteristics of tight oil reservoirs are similar. The main distribution is between 100~190 μm, and the average pore radius is 160 μm. While the distribution of the throat radius of tight sandstone and limestone is quite different, the distribution of the throat of sandstone samples is relatively concentrated, and the distribution of the throat of limestone samples is relatively sparse. There is a good positive correlation between the average throat radius and permeability, but the correlation between fractal dimension and permeability is not obvious. This indicates that the permeability is mainly affected by the radius of the throat. The pore-throat ratio in tight oil reservoirs is relatively large, and the resistance to seepage is greater during development. Therefore, during the development of tight oil, measures should be taken to increase the radius of the throat, reduce the ratio of pore radius to pore-throat radius, and improve the seepage capacity of the reservoir, thereby improving the development of tight oil.

Given the difficulty in developing waterflooding in tight oil reservoirs, using waterflooding huff-n-puff is an effective method to improve oil recovery. Online nuclear magnetic resonance (NMR) can detect the change in internal oil and water during the core displacement process, and magnetic resonance imaging (MRI) in real time. To improve the tight oil reservoir development effectiveness, cores with different permeability were selected for a waterflooding huff-n-puff experiment. Combined with online NMR equipment, the fluid saturation, recovery rate, and residual oil distribution were studied. The experiments showed that, for tight oil cores, more than 80% of the pores were sub-micro-and micro-nanopores. More than 77.8% of crude oil existed in the sub-micro-and micropores, and movable fluids mainly existed in the micropores with a radius larger than 1 µm. The NMR data and the MRI images both demonstrated that the recovery ratio of waterflooding after waterflooding huff-n-puff was higher than that of conventional waterflooding, and, therefore, residual oil was lower. Choosing two cycles' of waterflooding, huff-n-puff was more suitable for tight oil reservoir development. The production of crude oil increased by 22.2% in the field pilot test, which preliminarily proved that waterflooding huff-n-puff was suitable for tight oil reservoirs.