Vertically Stacked Amorphous Ir/Ru/Ir Oxide Nanosheets for Boosted Acidic Water Splitting.

Integrating multiple functional components into vertically stacked heterostructures offers a prospective approach to manipulating the physicochemical properties of materials. The synthesis of vertically stacked heterogeneous noble metal oxides remains a challenge. Herein, we report a surface segregation approach to create vertically stacked amorphous Ir/Ru/Ir oxide nanosheets (NSs). Cross-sectional high-angle annular darkfield scanning transmission electron microscopy images demonstrate a three-layer heterostructure in the amorphous Ir/Ru/Ir oxide NSs, with IrOx layers located on the upper and lower surfaces, and a layer of RuOx sandwiched between the two IrOx layers. The vertically stacked heterostructure is a result of the diffusion of Ir atoms from the amorphous IrRuOx solid solution to the surface. The obtained A-Ir/Ru/Ir oxide NSs display an ultralow overpotential of 191 mV at 10 mA cm-2 toward acid oxygen evolution reaction and demonstrate excellent performance in a proton exchange membrane water electrolyzer, which requires only 1.63 V to achieve 1 A cm-2 at 60 °C, with virtually no activity decay observed after a 1300 h test.

Amorphization-Induced Cation Exchange in Indium Oxide Nanosheets for CO2-to-Ethanol Conversion.

Cation exchange (CE) in metal oxides under mild conditions remains an imperative yet challenging goal to tailor their composition and enable practical applications. Herein, we first develop an amorphization-induced strategy to achieve room-temperature CE for universally synthesizing single-atom doped In2O3 nanosheets (NSs). Density functional theory (DFT) calculations elucidate that the abundant coordination-unsaturated sites present in a-In2O3 NSs are instrumental in surmounting the energy barriers of CE reactions. Empirically, a-In2O3 NSs as the host materials successfully undergo exchange with unary cations (Cu2+, Co2+, Mn2+, Ni2+), binary cations (Co2+Mn2+, Co2+Ni2+, Mn2+Ni2+), and ternary cations (Co2+Mn2+Ni2+). Impressively, high-loading single-atom doped (over 10 atom %) In2O3 NSs were obtained. Additionally, Cu/a-In2O3 NSs exhibit an excellent ethanol yield (798.7 µmol g-1 h-1) with a high selectivity of 99.5% for the CO2 photoreduction. This work offers a new approach to induce CE reactions in metal oxides under mild conditions and constructs scalable single-atom doped catalysts for critical applications.

Spiral Square Nanosheets Assembled from Ru Clusters.

Spiral two-dimensional (2D) nanosheets exhibit unique physical and chemical phenomena due to their twisted structures. While self-assembly of clusters is an ideal strategy to form hierarchical 2D structures, it is challenging to form spiral nanosheets. Herein, we first report a screw dislocation involved assembled method to obtain 2D spiral cluster assembled nanosheets (CANs) with uniform square morphology. The 2D spiral Ru CANs with a length of approximately 4 µm and thickness of 20.7 ± 3.0 nm per layer were prepared via the assembly of 1-2 nm Ru clusters in the presence of molten block copolymer Pluronic F127. Cryo-electron microscopy (cryo-EM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) demonstrate the existence of screw dislocation in the spiral assembled structure. The X-ray absorption fine structure spectrum indicates that Ru clusters are Ru3+ species, and Ru atoms are mainly coordinated with Cl with a coordination number of 6.5. Fourier-transform infrared (FT-IR) spectra and solid-state nuclear magnetic resonance hydrogen spectra (1H NMR) indicate that the assembly process of Ru clusters is formed by noncovalent interactions, including hydrogen bonding and hydrophilic interactions. Additionally, the Ru-F127 CANs exhibit excellent photothermal conversion performance in the near-infrared (NIR) region.

Quaternary (Fe/Ni)(P/S) mesoporous nanorods templated on stainless steel mesh lead to stable oxygen evolution reaction for over two months.

Synthesis of mesoporous (Fe/Ni)(P/S) dendritic nanorods on commercial 304L stainless steel mesh (SSM) was accomplished by initial anodic oxidation and subsequent co-sulfuration/phosphorization process. The mesoporous (Fe/Ni)(P/S) dendritic nanorods were obtained as a freestanding and stable catalyst for oxygen evolution reaction (OER). The mechanism of formation of mesoprous structure with nanorods is due to in-situ removal of Cr atoms (from the hard template of SSM) while the O2 bubbles released during OER served as dynamic bubble template (soft template). The as-prepared sample exhibited overpotentials of 173 mV at 10 mA cm-2 and 270 mV at 100 mA cm-2, which exceeded those that were recently reported using surface modified stainless steel-based catalysts for OER in alkaline condition. Moreover, the (Fe/Ni)(P/S) nanorods showed a remarkable Tafel slope of 65.7 mV dec-1 with stable activity beyond two months with only 2.5% fluctuation. The above outstanding performance could be attributed to the unique morphology with highly exposed active sites and the control of electronic structure by co-treatment with P and S. This work presents an efficient way to modify SSM for use as an inexpensive and durable OER catalyst.

Self-Supportive Mesoporous Ni/Co/Fe Phosphosulfide Nanorods Derived from Novel Hydrothermal Electrodeposition as a Highly Efficient Electrocatalyst for Overall Water Splitting.

Low cost and highly efficient bifuctional catalysts for overall water electrolysis have drawn considerable interests over the past several decades. Here, rationally synthesized mesoporous nanorods of nickel-cobalt-iron-sulfur-phosphorus composites are tightly self-supported on Ni foam as a high-performance, low cost, and stable bifunctional electrocatalyst for water electrolysis. The targeted designing and rational fabrication give rise to the nanorod-like morphology with large surface area and excellent conductivity. The NiCoFe-PS nanorod/NF can reach 10 mA cm-2 at a small overpotential of 195 mV with a Tafel slope of 40.3 mV dec-1 for the oxygen evolution reaction and 97.8 mV with 51.8 mV dec-1 for the hydrogen evolution reaction. Thus, this bifunctional catalyst shows low potentials of 1.52 and 1.76 V at 10 and 50 mA cm-2 toward overall water splitting with excellent stability for over 200 h, which are superior to most non-noble metal-based bifunctional electrocatalysts recently. This work provides a new strategy to fabricate multiple metal-P/S composites with the mesoporous nanorod-like structure as bifunctional catalysts for overall water splitting.