Electrocatalytic reduction of nitric oxide on Pt nanocrystals of different shape in sulfuric acid solutions

Vacancy-triggered and dopant-assisted NO electrocatalytic reduction over MoS2

Nitric oxide electroreduction reaction (NOER) is an efficient method for NH₃ synthesis and NO_x-related pollutant treatment. However, current research on NOER catalysts mainly focuses on noble metals and single atom catalysts, while low-cost transition metal dichalcogenides (TMDCs) are rarely considered. Herein, by applying density functional theory (DFT) calculations, we study the catalytic performance of NOER over 2H-MoS₂ monolayers with the most common S vacancies and some Mo atoms substituted by transition metal atoms (denoted as TM-MoS₂@V_S). Our results show that an S vacancy and a heteroatom substitution tend to form a first nearest neighbour (1NN) pair, which greatly improves the NOER catalytic performance of 2H-MoS₂. The S vacancy site can trigger NOER by strongly adsorbing a NO molecule and elongating the NO bond, while the heteroatom dopant can assist NOER by tuning the electron donating capability of 2H-MoS₂ which breaks the linear scaling relations among key reaction intermediates. At low NO coverage, NH₃ can be correspondingly yielded at -0.06 and -0.38 V onset potentials over the Pt- and Au-doped MoS₂ catalysts with S vacancies (Pt-MoS₂@V_S and Au-MoS₂@V_S). At high NO coverage, N₂O/N₂ is thermodynamically favored. Meanwhile, the competing hydrogen evolution reaction (HER) is suppressed. Thus, the Pt-MoS₂@V_S catalysts are promising candidates for NOER. In addition, coupling the substitutional doping of Mo atoms to S vacancies presents great potential in improving the catalytic activity and selectivity of MoS₂ for other reactions. In general, the strategy of coupling hetero-metal doping and chalcogen vacancy can be extended to enhance the catalytic activity of other TMDCs.

Nanoporous platinum electrode grown on anodic aluminum oxide membrane: Fabrication, characterization, electrocatalytic activity toward reactive oxygen and nitrogen species

A new type of nanoelectrode, nanoporous platinum (NPt) electrode was prepared on aluminum oxide membrane by thermal evaporation deposition. The morphology, conductivity and electrocatalytic activity of NPt electrode were characterized and compared with those of nanofilm-Pt electrode through scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques, respectively. SEM images showed that "nanocavities" observed in NPt electrode were actually 2-dimensional enclosures by linked nanoparticles. It was different from the conventional arrays of "nanocavities" formed on homogeneous metal films. EIS data indicated that NPt electrode possesses higher conductivity. Compared with that on nanofilm-Pt electrode (14.05 Ω·cm²), the impedance spectrum on NPt electrode exhibits a semicircle portion with much smaller diameters (1.24 Ω·cm² for NPt-100, 1.48 Ω·cm² for NPt-200). Meanwhile, the response sensitivity of NPt electrode to O₂ is 0.85 mA cm^-2, which is larger than that of nanofilm-Pt electrode (0.54 mA cm^-2). The largest catalytic current for nitric oxide (NO) was obtained in buffer with pH value of 9.4 while for Angeli^'s salt (AS) was obtained in buffer with pH value of 5.4. Additionally, electrocatalytic mechanisms of NPt electrode toward NO and AS were proposed, which indicating it depended on pH value of buffer solution.

Nanomaterials of high surface energy with exceptional properties in catalysis and energy storage

The properties of nanomaterials for use in catalytic and energy storage applications strongly depends on the nature of their surfaces. Nanocrystals with high surface energy have an open surface structure and possess a high density of low-coordinated step and kink atoms. Possession of such features can lead to exceptional catalytic properties. The current barrier for widespread industrial use is found in the difficulty to synthesise nanocrystals with high-energy surfaces. In this critical review we present a review of the progress made for producing shape-controlled synthesis of nanomaterials of high surface energy using electrochemical and wet chemistry techniques. Important nanomaterials such as nanocrystal catalysts based on Pt, Pd, Au and Fe, metal oxides TiO(2) and SnO(2), as well as lithium Mn-rich metal oxides are covered. Emphasis of current applications in electrocatalysis, photocatalysis, gas sensor and lithium ion batteries are extensively discussed. Finally, a future synopsis about emerging applications is given (139 references).

Structure sensitivity and nanoscale effects in electrocatalysis

This review discusses the role of the detailed nanoscale structure of catalytic surfaces on the activity of various electrocatalytic reactions of importance for fuel cells, hydrogen production, and other environmentally important catalytic reactions, such as carbon monoxide oxidation, methanol and ethanol oxidation, ammonia oxidation, nitric oxide reduction, hydrogen evolution, and oxygen reduction. Specifically, results and insights obtained from surface-science single-crystal-based model experiments are linked to experiments on well-defined shape-controlled nanoparticles. A classification of structure sensitive effects in electrocatalysis is suggested, based both on empirical grounds and on quantum-chemical viz. thermochemical considerations. The mutual relation between the two classification schemes is also discussed. The review underscores the relevance of single-crystal modeling of nanoscale effects in catalysis, and points to the special role of two kinds of active sites for electrocatalysis on nanoparticulate surfaces: (i) steps and defects in (111) terraces or facets, and (ii) long-range (100) terraces or facets.