Shape-Controlled Synthesis of Platinum-Based Nanocrystals and Their Electrocatalytic Applications in Fuel Cells.

To achieve environmentally benign energy conversion with the carbon neutrality target via electrochemical reactions, the innovation of electrocatalysts plays a vital role in the enablement of renewable resources. Nowadays, Pt-based nanocrystals (NCs) have been identified as one class of the most promising candidates to efficiently catalyze both the half-reactions in hydrogen- and hydrocarbon-based fuel cells. Here, we thoroughly discuss the key achievement in developing shape-controlled Pt and Pt-based NCs, and their electrochemical applications in fuel cells. We begin with a mechanistic discussion on how the morphology can be precisely controlled in a colloidal system, followed by highlighting the advanced development of shape-controlled Pt, Pt-alloy, Pt-based core@shell NCs, Pt-based nanocages, and Pt-based intermetallic compounds. We then select some case studies on models of typical reactions (oxygen reduction reaction at the cathode and small molecular oxidation reaction at the anode) that are enhanced by the shape-controlled Pt-based nanocatalysts. Finally, we provide an outlook on the potential challenges of shape-controlled nanocatalysts and envision their perspective with suggestions.

A NiCoP nanocluster-anchored porous Ti3C2Tx monolayer as high performance hydrogen evolution reaction electrocatalysts.

MXenes have received much attention as promising candidates for noble metal-free hydrogen evolution reaction (HER) electrocatalysts due to their high electrical conductivity, surface hydrophilicity, abundant surface functional groups, and great potential for rational hybridization with other materials. Herein, a novel porous monolayered-Ti3C2Tx@NiCoP (P-Ti3C2Tx@NiCoP) nanostructure was synthesized with uniform distribution of bimetallic compounds for improved charge transfer capability and electrocatalytic activity. In experiments, H2O2-utilized oxidation formed a highly mesoporous structure with a maximized surface area of monolayered MXenes as the support. A subsequent solvothermal process followed by phosphidation enabled successful anchoring of highly HER-active NiCoP nanoclusters onto abundantly exposed terminal edges of the P-Ti3C2Tx support. The structural porosity of the P-Ti3C2Tx nanoflakes played an important role in creating additional room for embedding catalytically active species while stably imparting high electrical conductivity to accelerate charge transfer to NiCoP nanoclusters. With structural modification and effective hybridization, P-Ti3C2Tx@NiCoP showed highly enhanced HER activity with significantly lower overpotentials of 115 and 101 mV at a current density of -10 mA cm-2 in 0.5 M H2SO4 and 1.0 M KOH, respectively, along with showing long-term stability over 60 h. As such, our approach of designing structurally modified-Ti3C2Tx and hybridizing with other electrocatalytically active species would function as a solid platform for implementing Ti3C2Tx-based hetero-nanostructures to achieve state-of-the-art performance in next-generation energy conversion applications.

Reduced graphene oxide-mediated Z-scheme BiVO4/CdS nanocomposites for boosted photocatalytic decomposition of harmful organic pollutants.

The efficient photocatalytic degradation of harmful organic pollutants (isoniazid (ISN) and 1,4-dioxane (DX)) via the Z-scheme electron transfer mechanism was accomplished using a photostable composite photocatalyst consisting of BiVO4, CdS, and reduced graphene oxide (RGO). Compared to their pristine counterparts, the RGO-mediated Z-scheme CdS/BiVO4 (CdS/RGO-BiVO4) nanocomposites exhibited superior degradation activities, mainly attributed to the prolonged charge separation. RGO was found to be involved in visible-light harvesting and acted as a solid-state electron mediator at the CdS/BiVO4 interface to realize an effective Z-scheme electron transfer pathway, avoid photocatalyst self-oxidation, and lengthen the life span of charge carriers. The results of reactive species scavenging experiments, photoluminescence measurements, and transient photocurrent measurements, as well as the calculated band potentials of the synthesized photocatalysts, supported the Z-scheme electron/hole pair separation mechanism. Additionally, the intermediates formed during the degradation of ISN and DX were identified, and a possible fragmentation pattern was proposed. This systematic work aims to develop photostable Z-scheme composites as unique photocatalytic systems for the efficient removal of harmful organic pollutants.

Enhanced visible light-driven photocatalytic performance of ZnO-g-C3N4 coupled with graphene oxide as a novel ternary nanocomposite.

This article reports a novel ternary nanocomposite consisting of ZnO, g-C3N4, and graphene oxide (GO) that provides enhanced photocatalytic performance and stability. The ZnO nanospheres disperse evenly and embed themselves in the porous g-C3N4. Composites with various g-C3N4 and GO to ZnO weight ratios were synthesized and characterized systematically. The results indicated that the absorption of binary g-C3N4/ZnO nanocomposites shifted to a lower energy compared to pure ZnO in a fashion consistent with the loading content of g-C3N4. Notably, the loading content of GO in the ZnO-g-C3N4 composite resulted in increased absorption in the visible range and improved charge separation efficiency, thereby drastically improving photocatalytic activity. Successful hybridization of ternary nanocomposite was confirmed by drastic quenching of fluorescence and broader visible light absorption. The optimal content of g-C3N4 in the ZnO-g-C3N4 composite was 50%, which exhibited the effective hybridization between ZnO and g-C3N4, and high photocatalytic efficiency. However, the photocatalytic degradation of the ternary nanocomposite showed performance that was two times greater than ZnO-g-C3N4, exhibiting 99.5% degradation efficiency after just 15 min of light irradiation. The combined heterojunction and synergistic effects of this composite account for the improved photocatalytic activity.

Comparative studies on influence of morphology and La doping on structural, optical, and photocatalytic properties of zinc oxide nanostructures.

A simple, low temperature co-precipitation method was developed to synthesize ZnO nanomaterials with different morphologies such as nanoflakes, spherical nanoparticles (SNPs), and nanorods. The concentration of the capping agent, Triton X-100, is a key factor in the morphological control of ZnO nanostructures. The formation of different morphologies of ZnO was confirmed by HR-SEM and HR-TEM. XRD data showed the formation of single-phase ZnO with the wurtzite crystal structure. The influence of La contents on the structure, morphology, absorption, emission, and photocatalytic activity of ZnO SNPs was investigated systematically. The influence of the ZnO morphologies on the photocatalytic degradation (PCD) of Bisphenol A (BPA) as a model reaction is evaluated and discussed in terms of surface area, crystal growth habits, particle size, and oxygen defects. The results indicated that the particle size is an important factor for the enhancement of PCD. Furthermore, the effect of different photocatalytic reaction parameters on the resulting PCD efficiency of ZnO SNPs was investigated.