Ammonia has emerged as a promising energy carrier owing to its carbon neutral content and low expense in long-range transportation. Therefore, development of a specific pathway to release the energy stored in ammonia is therefore in urgent demand. Electrochemical oxidation provides a convenient and reliable route to attain efficient utilization of ammonia. Here, we report that the high entropy (Mn, Fe, Co, Ni, Cu)₃O₄ oxides can achieve high electrocatalytic activity for ammonia oxidation reaction (AOR) in non-aqueous solutions. The AOR onset overpotential of (Mn, Fe, Co, Ni, Cu)₃O₄ is 0.70 V, which is nearly 0.2 V lower than that of their most active single metal cation counterpart. The mass spectroscopy study reveals that (Mn, Fe, Co, Ni, Cu)₃O₄ preferentially oxidizes ammonia to environmentally friendly diatomic nitrogen with a Faradic efficiency of over 85%. The X-ray photoelectron spectroscopy (XPS) result indicates that the balancing metal d-band of Mn and Cu cations helps retain a long-lasting electrocatalytic activity. Overall, this work introduces a new family of earth-abundant transition metal high entropy oxide electrocatalysts for AOR, thus heralding a new paradigm of catalyst design for enabling ammonia as an energy carrier.

Plasmonic photocatalysis represents the synergetic union of two active fields of research: plasmonic effects in illuminated metallic nanoparticles and catalytic effects in tailored metallic nanoparticles. Traditionally, metallic nanoparticles that excel for one application are limited for the other, but recent developments have shown that desirable catalytic behaviors, such as reduced activation barriers and improved product selectivity, derive from nonthermal behaviors uniquely produced by this synergy. After examining such findings, this review will address a specific debate that has recently surfaced: what is the relative degree of contributions of thermal and nonthermal effects in plasmonic photocatalysis? We demonstrate the importance of correctly accounting for thermal effects before characterizing nonthermal contributions. We show that another synergy occurs: these desirable nonthermal behaviors have a temperature dependence, and the resulting temperature-dependent reaction rates far exceed what can be explained from purely thermal effects alone. Thus, the synergy of plasmonic photocatalysis offers an exciting new contribution to the quest for efficient, selective, sustainable methods for chemical synthesis and energy conversion.

We reported the growth of horizontally aligned nitrogen-doped single-walled carbon nanotubes (SWNTs) on quartz substrates. The synthesized SWNTs were comprehensively characterized at the single nanotube level. Owing to the highly aligned nature of the nanotubes, we were able to investigate the diameter dependent doping mechanism through systematic resonant Raman spectroscopy studies. Other than the formerly found narrowing effect by N-doping, we proposed that the nanotube diameter affects the introduction of N atoms into the carbon lattice in an elaborate way. The obtained doping level increased along with the nanotube diameter but lost the increasing trend when the diameter became larger and experienced a slight decrease after reaching the local peak value. These insights about the heteroatom doping into the carbon nanotubes could benefit the development of the carbon nanotube based functional materials and extend their application in a broad range of areas.

In some cases, illumination of traditional thermal catalysts and tailored plasmonic photocatalysts may synergistically combine thermal and nonthermal mechanisms to enhance reaction rates and improve product selectivity at reduced temperatures. To understand how these attributes are achieved in plasmon-driven catalysis, these intertwined thermal and nonthermal effects must be untangled. Here, we show how a novel indirect illumination technique, in conjunction with precisely monitored thermal profiles of the catalyst, can confirm and clarify the role of nonthermal effects in plasmon-enhanced carbon dioxide methanation on a Rh/TiO₂ photocatalyst. We find that the extracted nonthermal methane production rate has a linear dependence on the top surface temperature, distinctly different from an exponential dependence for thermal catalysis. We also find that the apparent quantum efficiency from the nonthermal contribution has no dependence on light intensity but maintains a linear dependence on top surface temperatures between 200 and 350 ℃. The clear exposition of nonthermal effects in the Rh/TiO₂ plasmonic photocatalyst illustrates how this methodology may be applied for the quantitative evaluation of thermal and nonthermal light effects in other plasmon-enhanced catalytic reactions.

We demonstrated the controlled growth of two-dimensional (2D) hexagonal tin disulfide (SnS₂) nanoflakes with stacked monolayer atomic steps. The morphology was similar to flat-topped and step-sided mesa plateaus or step pyramids. The SnS₂ nanoflakes were grown on mica substrates via an atmospheric-pressure chemical vapor deposition process using tin monosulfide and sulfur powder as precursors. Atomic force microscopy (AFM), electron microscopy, and Raman characterizations were performed to investigate the structural features, and a sequential layer-wise epitaxial growth mechanism was revealed. In addition, systematic Raman characterizations were performed on individual SnS₂ nanoflakes with a wide range of thicknesses (1–100 nm), indicating that the A_1g peak intensity and Raman shifts were closely related to the thickness of the SnS₂ nanoflakes. Moreover, photoconductive AFM was performed on the monolayer-stepped SnS₂ nanoflakes, revealing that the flat surface and the edges of the SnS₂ atomic steps had different electrical conductive properties and photoconductive behaviors. This is ascribed to the dangling bonds and defects at the atomic step edges, which caused a height difference of the Schottky barriers formed at the interfaces between the PtIr-coated AFM tip and the step edges or the flat surface of the SnS₂ nanoflakes. The 2D SnS₂ crystals with regular monolayer atomic steps and fast photoresponsivity are promising for novel applications in photodetectors and integrated optoelectronic circuits.

High-quality carbon nanotubes (CNTs) are promising materials in many applications. However, current chemical vapor deposition (CVD) methods for CNT synthesis suffer from the discrepancy between the quality and yield of CNTs: Low-quality CNTs can be synthesized with high yield, while high-quality CNTs can only be synthesized with low yield. Here a CVD method has been designed to synthesize both high-quality and low-quality CNTs using the same combination of catalyst and precursor. As a result, we were able to understand the reasons for the low yield in high-quality CNT synthesis and a method was derived to improve their yield. This understanding is an important step towards high-yield synthesis of high-quality CNTs.

We present a bottom-up synthesis, spectroscopic characterization, and ab initio simulations of star-shaped hexagonal zinc oxide (ZnO) nanowires. The ZnO nanostructures were synthesized by a low-temperature hydrothermal growth method. The cross-section of the ZnO nanowires transformed from a hexagon to a hexagram when sulfur dopants from thiourea [SC(NH₂)₂] were added into the growth solution, but no transformation occurred when urea (OC(NH₂)₂) was added. Comparison of the X-ray photoemission and photoluminescence spectra of undoped and sulfur-doped ZnO confirmed that sulfur is responsible for the novel morphology. Large-scale theoretical calculations were conducted to understand the role of sulfur doping in the growth process. The ab initio simulations demonstrated that the addition of sulfur causes a local change in charge distribution that is stronger at the vertices than at the edges, leading to the observed transformation from hexagon to hexagram nanostructures.

We present a chemical vapor deposition (CVD) method for the growth of uniform single-walled carbon nanotube (SWNT) arrays on a stable temperature (ST)-cut single crystal quartz substrate using a mixture of methanol and ethanol as carbon source. It is found that introducing methanol during the growth can improve the density and the length of the well-aligned SWNTs in the arrays as well as increase the SWNT/quartz interaction. Obvious "up-shifts" of G-band frequencies in the Raman spectra have been found for the aligned SWNTs. A well-designed control experiment shows that the G-band "up-shifts" originate from the strong interaction between SWNTs and the quartz substrate. It is believed that exploring this interaction will help to elucidate the growth mechanism; ultimately, this will help realize the promise of controlling the chirality of SWNTs.

We demonstrate the role of catalysts in the surface growth of single-walled carbon nanotubes (SWNTs) by reviewing recent progress in the surface synthesis of SWNTs. Three effects of catalysts on surface synthesis are studied: type of catalyst, the relationship between the size of catalyst particles and carbon feeding rates, and interactions between catalysts and substrates. Understanding of the role of catalysts will contribute to our ability to control the synthesis of SWNTs on various substrates and facilitate the fabrication of nanotube-based devices.