Suxia Liang

Electroactive edge site-enriched nickel–cobalt sulfide into graphene frameworks for high-performance asymmetric supercapacitors

Tailor-made edge site-enriched inorganics coupled graphene hybrids hold a promising platform material for high-performance supercapacitors. Herein, we report a simple strategy for fabricating edge site-enriched nickel–cobalt sulfide (Ni–Co–S) nanoparticles decorated on graphene frameworks to form integrated hybrid architectures (Ni–Co–S/G) via an in situ chemically converted method. The Kirkendall effect-involved anion exchange reaction, e.g. the etching-like effort of the S2− ions, plays a crucial role for the formation of the edge site-enriched nanostructure. Density functional theory (DFT) calculations reveal that the Ni–Co–S edge sites have a high electrochemical activity and strong affinity for OH− in the electrolyte, which are responsible for the enhanced electrochemical performance. Benefiting from the integrated structures of Ni–Co–S nanoparticles and conductive graphene substrates, the resultant Ni–Co–S/G hybrid electrodes exhibit a high specific capacitance of 1492 F g−1 at the current density of 1 A g−1, a superior rate capability of 96% when the current density is increased to 50 A g−1, and excellent electrochemical stabilities. An asymmetric supercapacitor fabricated using the edge site-enriched Ni–Co–S/G hybrids as the positive electrode and porous carbon nanosheets (PCNS) as negative electrodes shows a high energy density of 43.3 W h kg−1 at a power density of 0.8 kW kg−1, and an energy density of 28.4 W h kg−1 can be retained even at a high power density of 22.1 kW kg−1.

The Power of Single‐Atom Catalysis

Single‐atom catalysts (SACs) with individual and isolated metal atoms anchored to supports can act as active centers. Single‐atom catalysis is powerful and attractive because SACs have demonstrated distinguishing performances, such as drastic cost‐reduction, notable catalytic activity, and selectivity. Herein, we firstly introduce SAC, including the concept and some key issues in synthesis and catalysis. Then, the power of single‐atom catalysis is highlighted and the most recent advances are summarized. It is very encouraging that in recent years our understanding of SACs has increased, owing to substantial studies regarding sample preparation, characterization, evaluation, and also mechanistic interpretation. On the other hand, great challenges still remain for SACs.

Single‐Atom Catalysis in Mesoporous Photovoltaics: The Principle of Utility Maximization

FeOx -supported single Pt atoms are used for the first time as counter electrodes (CEs) in dye-sensitized solar cells (DSCs), which are mesoporous photovoltaic devices. This system enables the investigation of the electrocatalytic behavior of a single-atom catalyst (SAC). Compared with conventional Pt CEs, the SAC-based CEs exhibit better reversibility as indicated by the peak-to-peak separation (Epp ). A high degree of atom utilization is demonstrated.

Electrocatalytic properties of iron chalcogenides as low-cost counter electrode materials for dye-sensitized solar cells

Developing cost-effective and highly electrocatalytic Pt-free counter electrode (CE) materials for triiodide reduction has become a major interest for dye-sensitized solar cells (DSCs). In a heterogeneous catalytic system, iron chalcogenides like FeS2 and FeSe2 have demonstrated excellent catalytic activity when serving as CE materials in DSCs. However, theoretical and experimental studies have yet to be conducted to investigate the catalytic activity of iron chalcogenides in energy conversion and storage devices under the same conditions. In this work, FeS2, FeSe2, and FeTe2 were selected as our research object to systematically investigate and compare the regulatory mechanisms of the changes in the catalytic activity of iron chalcogenides. Theoretical research reveals that the iodine adsorption and charge exchange of these three materials occurred efficiently in heterogeneous catalytic systems. Experimental results further show that these three materials exhibited excellent catalytic activities. The conversion efficiencies of the corresponding DSCs are comparable to those of the sputtered Pt CE. This study also provides a method to rationally screen cost-effective and highly efficient catalytic materials for electrocatalysis applications.

In-situ liquid cell transmission electron microscopy investigation on oriented attachment of gold nanoparticles

Inside a liquid solution, oriented attachment (OA) is now recognized to be as important a pathway to crystal growth as other, more conventional growth mechanisms. However, the driving force that controls the occurrence of OA is still poorly understood. Here, using in-situ liquid cell transmission electron microscopy, we demonstrate the ligand-controlled OA of citrate-stabilized gold nanoparticles at atomic resolution. Our data reveal that particle pairs rotate randomly at a separation distance greater than twice the layer thickness of adsorbed ligands. In contrast, when the particles get closer, their ligands overlap and guide the rotation into a directional mode until they share a common {111} orientation, when a sudden contact occurs accompanied by the simultaneous expulsion of the ligands on this surface. First-principle calculations confirm that the lower ligand binding energy on {111} surfaces is the intrinsic reason for the preferential attachment at this facet, rather than on other low-index facets.The non-classical oriented attachment crystallization pathway explains the growth of many nanocrystals. Here, the authors study citrate-stabilized gold nanoparticles by in-situ liquid transmission electron microscopy to reveal that surface ligands are a critical driving force in the oriented attachment process.