Showing papers on "Mesoporous material published in 2022"

Conformal quantum dot–SnO2 layers as electron transporters for efficient perovskite solar cells

Abstract: Improvements to perovskite solar cells (PSCs) have focused on increasing their power conversion efficiency (PCE) and operational stability and maintaining high performance upon scale-up to module sizes. We report that replacing the commonly used mesoporous–titanium dioxide electron transport layer (ETL) with a thin layer of polyacrylic acid–stabilized tin(IV) oxide quantum dots (paa-QD-SnO2) on the compact–titanium dioxide enhanced light capture and largely suppressed nonradiative recombination at the ETL–perovskite interface. The use of paa-QD-SnO2 as electron-selective contact enabled PSCs (0.08 square centimeters) with a PCE of 25.7% (certified 25.4%) and high operational stability and facilitated the scale-up of the PSCs to larger areas. PCEs of 23.3, 21.7, and 20.6% were achieved for PSCs with active areas of 1, 20, and 64 square centimeters, respectively. Description Tailoring tin oxide layers Mesoporous titanium dioxide is commonly used as the electron transport layer in perovskite solar cells, but electron transport layers based on tin(IV) oxide quantum dots could be more efficient, with a better-aligned conduction band and a higher carrier mobility. Kim et al. show that such quantum dots could conformally coat a textured fluorine-doped tin oxide electrode when stabilized with polyacrylic acid. Improved light trapping and reduced nonradiative recombination resulted in a certified power conversion efficiency of 25.4% and high operational stability. In larger-area minimodules, active areas as high as 64 square centimeters maintained certified power conversion efficiencies of more than 20%. —PDS Polymer-stabilized tin oxide nanoparticles suppress recombination at the electron-transport layer–perovskite interface.

Lattice‐Matching Formed Mesoporous Transition Metal Oxide Heterostructures Advance Water Splitting by Active Fe–O–Cu Bridges

Abstract: Developing efficient bifunctional electrocatalysts toward oxygen/hydrogen evolution reactions is crucial for electrochemical water splitting toward hydrogen production. The high‐performance electrocatalysts depend on the catalytically active and highly accessible reaction sites and their structural robustness, while the rational design of such electrocatalysts with desired features avoiding tedious manufacture is still challenging. Here, a facile method is reported to synthesize mesoporous and heterostructured transition metal oxides strongly anchored on a nickel skeleton (MH‐TMO) containing identified Fe–Cu oxide interfaces with high intrinsic activity, easy accessibility for reaction intermediates, and long‐term stability for alkaline oxygen/hydrogen evolution reactions. The MH‐TMO with the electrocatalytically active Fe–O–Cu bridge has an optimal oxygen binding energy to facilitate adsorption/desorption of oxygen intermediates for oxygen molecules. Associated with the high mass transport through the nanoporous structure, MH‐TMO exhibits impressive oxygen evolution reaction catalysis, with an extremely low overpotential of around 0.22 V at 10 mA cm−2 and low Tafel slope (44.5 mV dec−1) in 1.0 M KOH, realizing a current density of 100 mA cm−2 with an overpotential as low as 0.26 V. As a result, the alkaline electrolyzer assembled by the bifunctional MH‐TMO catalysts operates with an outstanding overall water‐splitting output (1.49 V@10 mA cm−2), outperforming one assembled with noble‐metal‐based catalysts.

Charge‐Enriched Strategy Based on MXene‐Based Polypyrrole Layers Toward Dendrite‐Free Zinc Metal Anodes

Abstract: Although zinc metal anodes have some intrinsic advantages for aqueous zinc ion batteries, the notorious dendrites hamper its practical applications. Herein, a charge‐enriched strategy through MXene‐based polypyrrole (MXene‐mPPy) layers is explored toward dendrite‐free Zn metal anode. The MXene‐mPPy layers composed of mesoporous PPy on both sides of Ti3C2Tx‐MXene exhibit an exceptional charge enrichment ability (149 F g−1, 5 mV s−1), which is beneficial not onlying terms of accumulating the charge levels, but also to homogenize the dispersions of electric field and ion flux as used as an artificial interface on a Zn anode. Thus, a dendrite‐free Zn anode with an ultralong cycling lifespan up to 2500 h and superior rate capability is achieved, which is further applied as an anode for aqueous zinc ion batteries with a long‐term span over 3000 cycles at 10 A g−1.

Sandwich‐Shell Structured CoMn2O4/C Hollow Nanospheres for Performance‐Enhanced Sodium‐Ion Hybrid Supercapacitor

Abstract: Sodium hybrid supercapacitors (Na‐HSCs) are regarded as one promising electrochemical energy storage device, because of the low price of sodium, prolonged life cycle, and high‐energy/power density. Nonetheless, the imparity between the fast capacitive reactions at cathode and the sluggish Faradaic reactions at the anode leads to an imbalance in the electrochemical reaction kinetics, limiting the development of Na‐HSCs. Therefore, it is urgent to develop suitable anode materials for performance‐enhanced Na‐HSCs. Herein, sandwich‐shell‐structured CoMn2O4/C hollow spheres are synthesized by a facile hydrothermal reaction and subsequent calcination, where mesoporous carbon hollow spheres (CHSs) serve as nonsacrificial hard templates. CHSs with numerous mesoporous channels are beneficial for the penetration of reactant ions. Therefore, CoMn2O4 nanosheets are successfully deposited on the inner and outer surfaces of CHSs, generating sandwich‐shell‐structured CoMn2O4/C hollow spheres. Benefiting from the unique design, CoMn2O4/C HSs exhibit excellent sodium storage performance, including a high‐specific capacity of 290 mAh g–1 at 0.1 A g–1 and prolonged cycling durability. A Na‐HSC assembled by CoMn2O4/C HSs anode and activated carbon cathode exhibits a high‐energy density (265 Wh kg–1) and a wide‐operating voltage range (0.01–4.0 V).

Spatial Confinement Strategy for Micelle-Size-Mediated Modulation of Mesopores in Hierarchical Porous Carbon Nanosheets with an Efficient Capacitive Response.

Abstract: Commercial supercapacitors using available carbon products have long been criticized for the under-utilization of their prominent specific surface area (SSA). In terms of carbonaceous electrode optimization, excessive improvement in SSA observed in the gaseous atmosphere might have little effect on the final performance because cracked/inaccessible pore alleys considerably block the direct electrolyte ion transport in a practical electrochemical environment. Herein, mesopore-adjustable hierarchically porous carbon nanosheets are fabricated based on a micelle-size-mediated spatial confinement strategy. In this strategy, hydrophobic trimethylbenzene in different volumes of the solvent can mediate the interfacial assembly with a carbon precursor and porogen segment through π-π bonding and van der Waals interaction to yield micelles with good dispersity and the diameter varying from 119 to 30 nm. With an increasing solvent volume, the corresponding diffusion coefficient (3.1-14.3 m2 s-1) of as-obtained smaller micelles increases, which makes adjacent micelles gather rapidly and then grow along the radial direction of oligomer aggregates to eventually form mesopores on hierarchically porous carbon nanosheets (MNC150-4.5). Thanks to the pore-expansion effect of trimethylbenzene, the mesoporous volume can be adjusted from 28.8 to 40.0%. Mesopores on hierarchically porous carbon nanosheets endow MNC150-4.5 with an enhanced electrochemically active surface area of 819.5 m2 g-1, which gives rise to quick electrolyte accessibility and a correspondingly immediate capacitive response of 338 F g-1 at 0.5 A g-1 in a three-electrode system. Electrolyte transport through pathways within MNC150-4.5 ultimately enables the symmetric cell to deliver a high energy output of 50.4 Wh kg-1 at 625 W kg-1 in a 14 m LiOTF electrolyte and 95% capacitance retention after 100,000 cycles, which show its superior electrochemical performance over representative carbon-based supercapacitors with aqueous electrolytes in recent literature.

Self-Assembly of Ir-Based Nanosheets with Ordered Interlayer Space for Enhanced Electrocatalytic Water Oxidation.

Abstract: Iridium (Ir)-based electrocatalysts are widely explored as benchmarks for acidic oxygen evolution reactions (OERs). However, further enhancing their catalytic activity remains challenging due to the difficulty in identifying active species and unfavorable architectures. In this work, we synthesized ultrathin Ir-IrOx/C nanosheets with ordered interlayer space for enhanced OER by a nanoconfined self-assembly strategy, employing block copolymer formed stable end-merged lamellar micelles. The interlayer distance of the prepared Ir-IrOx/C nanosheets was well controlled at ∼20 nm and Ir-IrOx nanoparticles (∼2 nm) were uniformly distributed within the nanosheets. Importantly, the fabricated Ir-IrOx/C electrocatalysts display one of the lowest overpotential (η) of 198 mV at 10 mA cm-2geo during OER in an acid medium, benefiting from their features of mixed-valence states, rich electrophilic oxygen species (O(II-δ)-), and favorable mesostructured architectures. Both experimental and computational results reveal that the mixed valence and O(II-δ)- moieties of the 2D mesoporous Ir-IrOx/C catalysts with a shortened Ir-O(II-δ)- bond (1.91 Å) is the key active species for the enhancement of OER by balancing the adsorption free energy of oxygen-containing intermediates. This strategy thus opens an avenue for designing high performance 2D ordered mesoporous electrocatalysts through a nanoconfined self-assembly strategy for water oxidation and beyond.

Fabrication of Flexible Mesoporous Black Nb2O5 Nanofiber Films for Visible‐Light‐Driven Photocatalytic CO2 Reduction into CH4

Abstract: Achieving high selectivity and conversion efficiency simultaneously is a challenge for visible‐light‐driven photocatalytic CO2 reduction into CH4. Here, a facile nanofiber synthesis method and a new defect control strategy at room‐temperature are reported for the fabrication of flexible mesoporous black Nb2O5 nanofiber catalysts that contain abundant oxygen‐vacancies and unsaturated Nb dual‐sites, which are efficient towards photocatalytic production of CH4. The oxygen‐vacancy decreases the bandgap width of Nb2O5 from 3.01–2.25 eV, which broadens the light‐absorption range from ultraviolet to visible‐light, and the dual sites in the mesopores can easily adsorb CO2, so that the intermediate product of CO* can be spontaneously changed into *CHO. The formation of a highly stable NbCHO* intermediate at the dual sites is proposed to be the key feature determining selectivity. The preliminary results show that without using sacrificial agents and photosensitizers, the nanofiber catalyst achieves 64.8% selectivity for CH4 production with a high evolution rate of 19.5 µmol g−1 h−1 under visible‐light. Furthermore, the flexible catalyst film can be directly used in devices, showing appealing and broadly commercial applications.

Crystalline-amorphous interface of mesoporous Ni2P@FePOxHy for oxygen evolution at high current density in alkaline-anion-exchange-membrane water-electrolyzer

Abstract: For industrial high-purity hydrogen production, it is essential to develop low-cost, earth-abundant, highly-efficient, and stable electrocatalysts which deliver high current density (j) at low overpotential (η) for oxygen evolution reaction (OER). Herein, we report an active mesoporous Ni 2 P @ FePO x H y pre-electrocatalyst, which delivers high j = 1 A cm −2 at η = 360 mV in 1 M KOH with long-term durability (12 days), fulfilling all the desirable commercial criteria for OER. The electrocatalyst shows abundant interfaces between crystalline metal phosphide and amorphous phosphorus-doped metal-oxide, improving charge transfer capability and providing access to rich electroactive sites. Combined with an excellent non-noble metal-based HER catalyst, we achieve commercially required j = 500/1000 mA cm −2 at 1.65/1.715 V for full water-splitting with excellent stability in highly corrosive alkaline environment (30% KOH). The alkaline-anion-exchange-membrane water-electrolyzer (AAEMWE) fabricated for commercial viability exhibits high j of 1 A cm −2 at 1.84 V with long-term durability as an economical hydrogen production method, outperforming the state-of-the-art Pt/C – IrO 2 catalyst. • Noble-metal free catalysts for oxygen evolution reactions are investigated. • Crystalline (Ni 2 P) and amorphous (FePO x H y ) phases in Ni 2 P @ FePO x H y catalyst provide more electrocatalytic active sites. • The Ni 2 P @ FePO x H y catalyst shows excellent AAEMWE cell performance with a low overpotential and good stability. • The Ni 2 P @ FePO x H y catalyst exhibits a low overpotential of 360 mV for OER to deliver a high current density of 1 A cm −2 .

Covalent organic framework–based porous ionomers for high-performance fuel cells

Abstract: Lowering platinum (Pt) loadings without sacrificing power density and durability in fuel cells is highly desired yet challenging because of the high mass transport resistance near the catalyst surfaces. We tailored the three-phase microenvironment by optimizing the ionomer by incorporating ionic covalent organic framework (COF) nanosheets into Nafion. The mesoporous apertures of 2.8 to 4.1 nanometers and appendant sulfonate groups enabled the proton transfer and promoted oxygen permeation. The mass activity of Pt and the peak power density of the fuel cell with Pt/Vulcan (0.07 mg of Pt per square centimeter in the cathode) both reached 1.6 times those values without the COF. This strategy was applied to catalyst layers with various Pt loadings and different commercial catalysts. Description Helping fuel cells breathe In proton exchange membrane fuel cells, the Nafion ionomer usually overencapsulates and inhibits the platinum catalyst and can impede gas transport in the catalyst layer. Q. Zhang et al. showed that adding a sulfonated covalent organic framework (COF) to Nafion could improve the activity based on platinum by up to 60% (see the Perspective by Ma and Lutkenhaus). The hexagonal pores of the COF improve gas transport, and the sulfonic acid groups anchored on the pore walls decrease binding to platinum, which inhibits its activity. —PDS Adding a sulfonated ionic covalent organic framework into the Nafion ionomer improves gas transport to the catalyst layer.

A hierarchically porous Fe-N-C synthesized by dual melt-salt-mediated template as advanced electrocatalyst for efficient oxygen reduction in zinc-air battery

Abstract: The reasonable design of porous structures is important but usually overlooked for nonprecious metal ORR catalysts. In this study, a facile dual melt-salt-mediated templating method is developed to prepare a Fe-N-C catalyst with tailored porous framework. The ZnCl2 and NaCl are employed to construct abundant micropores and promote the transformation of partial micropores to mesopores, respectively, reasonably forming a 3D hierarchically porous framework. The catalyst demonstrates a satisfactory surface area (1605 m2/g), promoting mass transport and exposure of FeN4 sites. Interestingly, the dual melt-salt templates avoid rapid loss of nitrogen during pyrolysis, thus enhancing Fe-N4 active center density. Therefore, the obtained Fe-N-C material presents outstanding ORR performance in both alkaline and acid media, as well as good stability. The advances of this catalyst are further proved in liquid and solid-state Zn-air battery, with nice discharge stability and high peak power densities.

Selective ligand removal to improve accessibility of active sites in hierarchical MOFs for heterogeneous photocatalysis

Abstract: Abstract Metal-organic frameworks (MOFs) are commended as photocatalysts for H 2 evolution and CO 2 reduction as they combine light-harvesting and catalytic functions with excellent reactant adsorption capabilities. For dynamic processes in liquid phase, the accessibility of active sites becomes a critical parameter as reactant diffusion is limited by the inherently small micropores. Our strategy is to introduce additional mesopores by selectively removing one ligand in mixed-ligand MOFs via thermolysis. Here we report photoactive MOFs of the MIL-125-Ti family with two distinct mesopore architectures resembling either large cavities or branching fractures. The ligand removal is highly selective and follows a 2-step process tunable by temperature and time. The introduction of mesopores and the associated formation of new active sites have improved the HER rates of the MOFs by up to 500%. We envision that this strategy will allow the purposeful engineering of hierarchical MOFs and advance their applicability in environmental and energy technologies.

Covalent Organic Frameworks with Record Pore Apertures.

Abstract: The pore apertures dictate the guest accessibilities of the pores, imparting diverse functions to porous materials. It is highly desired to construct crystalline porous polymers with predesignable and uniform mesopores that can allow large organic, inorganic, and biological molecules to enter. However, due to the ease of the formation of interpenetrated and/or fragile structures, the largest pore aperture reported in the metal-organic frameworks is 8.5 nm, and the value for covalent organic frameworks (COFs) is only 5.8 nm. Herein, we construct a series of COFs with record pore aperture values from 7.7 to 10.0 nm by designing building blocks with large conformational rigidness, planarity, and suitable local polarity. All of the obtained COFs possess eclipsed stacking structures, high crystallinity, permanent porosity, and high stability. As a proof of concept, we successfully employed these COFs to separate pepsin that is ∼7 nm in size from its crudes and to protect tyrosinase from heat-induced deactivation.

Shielding Protection by Mesoporous Catalysts for Improving Plasma-Catalytic Ambient Ammonia Synthesis

Abstract: Plasma catalysis is a promising technology for decentralized small-scale ammonia (NH3) synthesis under mild conditions using renewable energy, and it shows great potential as an alternative to the conventional Haber–Bosch process. To date, this emerging process still suffers from a low NH3 yield due to a lack of knowledge in the design of highly efficient catalysts and the in situ plasma-induced reverse reaction (i.e., NH3 decomposition). Here, we demonstrate that a bespoke design of supported Ni catalysts using mesoporous MCM-41 could enable efficient plasma-catalytic NH3 production at 35 °C and 1 bar with >5% NH3 yield at 60 kJ/L. Specifically, the Ni active sites were deliberately deposited on the external surface of MCM-41 to enhance plasma–catalyst interactions and thus NH3 production. The desorbed NH3 could then diffuse into the ordered mesopores of MCM-41 to be shielded from decomposition due to the absence of plasma discharge in the mesopores of MCM-41, that is, “shielding protection”, thus driving the reaction forward effectively. This promising strategy sheds light on the importance of a rational design of catalysts specifically for improving plasma-catalytic processes.