Nonprecious transition-metal phosphides (TMPs) are versatile materials with tunable electronic and structural properties that could be promising as catalysts for energy conversion applications. Despite the facts, TMPs are not explored thoroughly to understand the chemistry behind their rich catalytic properties for the water splitting reaction. Herein, spiky ball-shaped monodispersed TMP nanoparticles composed of Fe, Co, and Ni are developed and used as efficient electrocatalysts for hydrogen and oxygen evolution reaction (HER, OER), and overall water splitting in alkaline medium; and their surface chemistry was explored to understand the reaction mechanism. The optimized Fe0.5CoNi0.5P catalyst shows attractive activities of HER and OER with low overpotentials and Tafel slopes, and with high mass activities, turnover frequencies, and exchange current densities. When applied to overall water splitting, the electrolyzer Fe0.5CoNi0.5P||Fe0.5CoNi0.5P cell can reach a 10 mA cm–2 current density at cell voltages of only 1.52 and 1.56 V in 1.0 M and 30 wt % KOH, respectively, much lower than those of commercial IrO2||Pt/C. The optimized electrolyzer with sizable numbers of chemically active sites exhibits superior durability up to 70 h and 5000 cycles in 1.0 M KOH and can attain a current density as high as 1000 mA cm–2, showing a class of efficient bifunctional electrocatalysis. Experimental and density functional theory-based mechanistic analyses reveal that surface reconstruction takes place in the presence of KOH to form the TMP precatalyst, which results in high coverage of oxygen active species for the OER with a low apparent activation energy (Ea) for conversion of *OOH to O2. These also evidenced the thermoneutral adsorption of H* for the efficient HER half-reaction.
Carbon Aerogels Subhajit Kundu, Debarati Mitra, Mahuya Das Aerogel is a porous solid material derived from gel in which the liquid is replaced by gas. The wide application of aerogel in the field of adsorbent is due to its macro dimension. It can be removed very easily from an aqueous reaction medium in comparison to […]
An eco-friendly approach for fabrication of AuPd–rGO–PEG nanocomposites and their excellent activity towards in vitro photothermal ablation of HeLa cells.
Graphene is one of the most interesting materials in the field of nanoscience and nanotechnology. Metal oxide nanoparticles exhibit unique physical and chemical properties due to their reduced size and high density of corner or edge surface sites. The metal oxide-graphene nanocomposites not only possess favorable properties of graphene and metal oxide, but also greatly enhance the intrinsic properties due to the synergistic effect between them. These composites are used for catalysis, supercapacitors, lithium ion batteries, solar cells, sensors, removal of pollutants from water, etc. There is a very broad scope of further research for the development of metal oxide-graphene nanocomposites with enhanced properties for different applications. This chapter deals with a comprehensive review of the current research activities from the viewpoint of chemistry and materials science with a special focus on the synthesis, characterization, and applications of metal oxide-graphene nanocomposite materials.
Nanoheterostructures (NHSs) based on lead halide perovskites (LHPs) and chalcogenide quantum dots have proved to be promising candidates for photovoltaic device applications. However, understanding the defect chemistry at the interfaces of LHPs and chalcogenides is essential to stabilize them and further tune their optoelectronic properties. Here, we demonstrate a route for designing CsPbBr3–PbSe NHSs and other derivatives of LHP-based NHSs using defect-rich MoSe2 nanosheets (NSs) and study the effect of the size of PbSe NPs on their optical properties. In this synthesis route, PbSe nanoparticles (NPs) are formed at an early stage of the reaction through a unique cation displacement reaction, over which CsPbBr3 nanocrystals (NCs) are epitaxially grown. Using this methodology, a nearly 3-fold enhancement in photoluminescence (PL) is achieved, whereas other selenium precursors, which form larger PbSe NPs, result in negligible PL enhancement with respect to the pure CsPbBr3 NCs. Detailed density functional theory (DFT) calculations suggest that the PbSe NPs are responsible for passivating the surface defects that consequently enhance the PL intensity. However, in the case of larger PbSe NPs, the associated valence and conduction bands lie within the band-gap region of CsPbBr3, creating a type-I heterostructure between the two materials, thereby affecting the luminescence properties. Strong passivation of surface defects in CsPbBr3–PbSe NHSs is also evidenced from low-temperature PL studies. Furthermore, the resulting CsPbBr3–PbSe NHSs demonstrate enhanced stability in the presence of water and do not degrade under ambient conditions for several months.
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