Atomic interface regulation is thought to be an efficient method to adjust the performance of single atom catalysts. Herein, a practical strategy was reported to rationally design single copper atoms coordinated with both sulfur and nitrogen atoms in metal-organic framework derived hierarchically porous carbon (S-Cu-ISA/SNC). The atomic interface configuration of the copper site in S-Cu-ISA/SNC is detected to be an unsymmetrically arranged Cu-S 1 N 3 moiety. The catalyst exhibits excellent oxygen reduction reaction activity with a half-wave potential of 0.918 V vs. RHE. Additionally, through in situ X-ray absorption fine structure tests, we discover that the low-valent Cuprous-S 1 N 3 moiety acts as an active center during the oxygen reduction process. Our discovery provides a universal scheme for the controllable synthesis and performance regulation of single metal atom catalysts toward energy applications.

Photoacoustic imaging is a non-ionizing imaging modality that provides contrast consistent with optical imaging techniques while the resolution and penetration depth is similar to ultrasound techniques. In a previous publication [Opt. Express 18, 11406 (2010)], a technique was introduced to experimentally acquire the imaging operator for a photoacoustic imaging system. While this was an important foundation for future work, we have recently improved the experimental procedure allowing for a more densely populated imaging operator to be acquired. Subsets of the imaging operator were produced by varying the transducer count as well as the measurement space temporal sampling rate. Examination of the matrix rank and the effect of contributing object space singular vectors to image reconstruction were performed. For a PAI system collecting only limited data projections, matrix rank increased linearly with transducer count and measurement space temporal sampling rate. Image reconstruction using a regularized pseudoinverse of the imaging operator was performed on photoacoustic signals from a point source, line source, and an array of point sources derived from the imaging operator. As expected, image quality increased for each object with increasing transducer count and measurement space temporal sampling rate. Using the same approach, but on experimentally sampled photoacoustic signals from a moving point-like source, acquisition, data transfer, reconstruction and image display took 1.4 s using one laser pulse per 3D frame. With relatively simple hardware improvements to data transfer and computation speed, our current imaging results imply that acquisition and display of 3D photoacoustic images at laser repetition rates of 10Hz is easily achieved.

The development of efficient and cost-effective catalysts to catalyze a wide variety of electrochemical reactions is key to realize the large-scale application of renewable and clean energy technologies. Owing to the maximum atom-utilization efficiency and unique electronic and geometric structures, single atom catalysts (SACs) have exhibited superior performance in various catalytic systems. Recently, assembled from the functionalized organic linkers and metal nodes, metal-organic frameworks (MOFs) with ultrafine porosity have received tremendous attention as precursors or self-sacrificing templates for preparing porous SACs. Here, the recent advances toward the synthesis strategies for using MOF precursors/templates to construct SACs are systematically summarized with special emphasis on the types of central metal sites. The electrochemical applications of these recently emerged MOF-derived SACs for various energy-conversion processes, such as oxygen reduction/evolution reaction (ORR/OER), hydrogen evolution reaction (HER), and CO 2 reduction reaction (CO 2 RR), are also discussed and reviewed. Finally, the current challenges and prospects regarding the development of MOF-derived SACs are proposed.

Exploring efficient and cost-effective catalysts to replace precious metal catalysts, such as Pt, for electrocatalytic oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) holds great promise for renewable energy technologies. Herein, we prepare a type of Co catalyst with single-atomic Co sites embedded in hierarchically ordered porous N-doped carbon (Co-SAS/HOPNC) through a facile dual-template cooperative pyrolysis approach. The desirable combination of highly dispersed isolated atomic Co-N4 active sites, large surface area, high porosity, and good conductivity gives rise to an excellent catalytic performance. The catalyst exhibits outstanding performance for ORR in alkaline medium with a half-wave potential (E1/2) of 0.892 V, which is 53 mV more positive than that of Pt/C, as well as a high tolerance of methanol and great stability. The catalyst also shows a remarkable catalytic performance for HER with distinctly high turnover frequencies of 0.41 and 3.8 s−1 at an overpotential of 100 and 200 mV, respectively, together with a long-term durability in acidic condition. Experiments and density functional theory (DFT) calculations reveal that the atomically isolated single Co sites and the structural advantages of the unique 3D hierarchical porous architecture synergistically contribute to the high catalytic activity.

By the in situ X-ray absorption results, the gradually decrease of Cu oxidation state under applied potential implied that low-valence Cu (+1) species in the atomic interface of Cu–N4–C8S2 may work as the catalytic sites during an ORR process.

Herein, we report efficient single copper atom catalysts that consist of dense atomic Cu sites dispersed on a three-dimensional carbon matrix with highly enhanced mesoporous structures and improved active site accessibility (Cu-SA/NC­(meso)). The ratio of +1 to +2 oxidation state of the Cu sites in the Cu-SA/NC­(meso) catalysts can be controlled by varying the urea content in the adsorption precursor, and the activity for ORR increases with the addition of Cu1+ sites. The optimal Cu1+-SA/NC­(meso)-7 catalyst with highly accessible Cu1+ sites exhibits superior ORR activity in alkaline media with a half-wave potential (E 1/2) of 0.898 V vs RHE, significantly exceeding the commercial Pt/C, along with high durability and enhanced methanol tolerance. Control experiments and theoretical calculations demonstrate that the superior ORR catalytic performance of Cu1+-SA/NC­(meso)-7 catalyst is attributed to the atomically dispersed Cu1+ sites in catalyzing the reaction and the advantage of the introduced mesoporous structure in enhancing the mass transport.

We report the preparation and use of the three-dimensionally ordered mesoporous Ni sphere arrays (3D-OMNiSA) as a highly effective OER catalyst in alkaline electrolyte. The 3D-OMNiSA is fabricated through lyotropic liquid crystal templating within a polymer inverse opal. The prepared 3D-OMNiSA catalyst exhibits a low overpotential of 254 mV at 10 mA cm −2 and a small Tafel slope of 39 mV decade −1 , better than the commercial precious RuO 2 catalyst. The mass activity (166.5 A g −1 ) and turnover frequency (0.0281 s −1 ) of 3D-OMNiSA are about 4.3 and 2.2 times that of RuO 2 , respectively. Additionally, this 3D-OMNiSA catalyst shows a high durability under harsh water oxidation cycling test. The outstanding OER performance of the 3D-OMNiSA could be attributed to the large surface area, efficient mass and charge transport, and high structural stability arising from the unique 3D hierarchical porous structure of the 3D-OMNiSA consisting of ordered close-packed mesoporous spheres.

The serious shuttle effect, sluggish reduction kinetics of polysulfides and the difficult oxidation reaction of Li 2 S have hindered LiS battery practical application. Herein, a 3D hierarchical structure composed of NiMoO 4 nanosheets in situ anchored on NS doped carbon clothes (NiMoO 4 @NSCC) as the free-standing host is creatively designed and constructed for LiS battery. Dual transitional metal oxide (NiMoO 4 ) increases the electrons density near the Fermi level due to the contribution of the incorporating molybdenum (Mo), leading to the smaller bandgap, and thus stronger metallic properties compared with NiO. Furthermore, as a bidirectional catalyst, NiMoO 4 is proposed to facilitate reductions of polysulfides through lengthening the SS bond distance of Li 2 S 4 and reducing the free energy of polysulfides conversion, meanwhile promote critical oxidation of insulative discharge product (Li 2 S) via lengthening LiS bond distance of Li 2 S and decreasing Li 2 S decomposition barrier. Therefore, after loading sulfur (2 mg cm −2 ), NiMoO 4 @NSCC/S as the self-supporting cathode for the LiS battery exhibits impressive long cycle stability. This study proposes a concept of a bidirectional catalyst with dual metal oxides, which would supply a novel vision to construct the high-performance LiS battery.