Ultrathin Ce-doped La2O3nanofilm electrocatalysts for efficient oxygen evolution reactions.

It is still highly desired to develop efficient, resource-abundant and inexpensive electrocatalysts to improve the sluggish kinetics of oxygen evolution reaction (OER) in electrochemical water splitting systems. In this work, the large-area ultrathin (2.52 nm thick) Ce-doped La2O3nanofilms were developed via a facile and reliable ionic layer epitaxy method with different Ce content. The ultrathin Ce-doped La2O3nanofilm with optimum composition of La1.22Ce0.78O3exhibited an excellent OER performance with a very low overpotential of 221 mV at 10 mA cm-2and a small Tafel slope of 33.7 mV dec-1. A remarkable high mass activity of 6263.2 A g-1was also obtained from ultrathin La1.22Ce0.78O3nanofilm at the overpotential of 221 mV. Such a high mass activity was three orders of magnitude higher than state-of-the-art commercial IrO2powders (3.8 A g-1) and more than 30 times higher than La2O3nanofilm (196.7 A g-1) without Ce doping at the same overpotential. This high mass activity was even significantly higher than other recently reported typical OER catalysts. The substantial OER performance gain by the Ce doping was attributed to the improved conductivity and electrochemical active surface areas of nanofilms as a result of favorable tuning on the charge transfer and electronic structures. This work provides a promising approach to develop high-performance two-dimensional (2D) electrocatalysts by effective heteroatom doping strategy.

Mesoporous Ultrathin In2O3 Nanosheet Cocatalysts on a Silicon Nanowire Photoanode for Efficient Photoelectrochemical Water Splitting.

Vertical Si nanowire (NW) arrays are a promising photoanode material in the photoelectrochemical (PEC) water splitting field because of their highly efficient light absorption capability and large surface areas for PEC reactions. However, Si NW arrays always suffer from high overpotential, low photocurrent density, and low applied bias photon-to-current efficiency (ABPE) due to their low surface catalytic activity and intense charge recombination. Here, we report an efficient oxygen evolution cocatalyst of optically transparent, mesoporous ultrathin (2.47 nm thick) In2O3 nanosheets, which are coupled on the top of Si NW arrays. Combined with a conformal TiO2 thin film as an intermediate protective layer, this Si NW/TiO2/In2O3 (2.47 nm) heterostructured photoanode exhibited an extremely low onset potential of 0.6 V vs reversible hydrogen electrode (RHE). The Si NW/TiO2/In2O3 (2.47 nm) photoanode also showed a high photocurrent density of 27 mA cm-2 at 1.23 V vs RHE, more than 1 order of magnitude higher than that of the Si NW/TiO2 photoanodes. This improvement in solar water splitting performance was attributed to the significantly promoted charge injection efficiency as a result of the In2O3 nanosheet coupling. This work presents a promising pathway for developing efficient Si-based photoanodes by coupling ultrathin 2D cocatalysts.

Nanoparticle-Decorated Ultrathin La2O3 Nanosheets as an Efficient Electrocatalysis for Oxygen Evolution Reactions.

Electrochemical catalysts for oxygen evolution reaction are a critical component for many renewable energy applications. To improve their catalytic kinetics and mass activity are essential for sustainable industrial applications. Here, we report a rare-earth metal-based oxide electrocatalyst comprised of ultrathin amorphous La2O3 nanosheets hybridized with uniform La2O3 nanoparticles (La2O3@NP-NS). Significantly improved OER performance is observed from the nanosheets with a nanometer-scale thickness. The as-synthesized 2.27-nm La2O3@NP-NS exhibits excellent catalytic kinetics with an overpotential of 310 mV at 10 mA cm-2, a small Tafel slope of 43.1 mV dec-1, and electrochemical impedance of 38 Ω. More importantly, due to the ultrasmall thickness, its mass activity, and turnover frequency reach as high as 6666.7 A g-1 and 5.79 s-1, respectively, at an overpotential of 310 mV. Such a high mass activity is more than three orders of magnitude higher than benchmark OER electrocatalysts, such as IrO2 and RuO2. This work presents a sustainable approach toward the development of highly efficient electrocatalysts with largely reduced mass loading of precious elements.

Enhanced Ferromagnetism from Organic-Cerium Oxide Hybrid Ultrathin Nanosheets.

Room-temperature ferromagnetism in two-dimensional (2D) oxide materials is an intriguing phenomenon for spintronic applications. Here, we report significantly enhanced room-temperature ferromagnetism observed from ultrathin cerium oxide nanosheets hybridized with organic surfactant molecules. The hybrid nanosheets were synthesized by ionic layer epitaxy over a large area at the water-air interface. The nanosheets exhibited a saturation magnetization of 0.149 emu/g as their thickness reduced to 0.67 nm. This value was 5 times higher than that for CeO2 thin films and more than 20 times higher than that for CeO2 nanoparticles. The magnetization was attributed to the high concentration (15.5%) of oxygen vacancies stabilized by surfactant hybridization as well as electron transfer between organic and oxide layers. This work brings an effective strategy of introducing strong ferromagnetism to functional oxide materials, which leads to a promising route toward exploring new physical properties in 2D hybrid nanomaterials.