Hierarchical Porous Activated Carbon Derived from Coconut Shell for Ultrahigh-Performance Supercapacitors.

In this research, we successfully produced hierarchical porous activated carbon from biowaste employing one-step KOH activation and applied as ultrahigh-performance supercapacitor electrode materials. The coconut shell-derived activated carbon (CSAC) features a hierarchical porous structure in a honeycomb-like morphology, leading to a high specific surface area (2228 m2 g-1) as well as a significant pore volume (1.07 cm3 g-1). The initial test with the CSAC electrode, conducted in a 6 M KOH loaded symmetric supercapacitor, demonstrated an ultrahigh capacitance of 367 F g-1 at a current density of 0.2 A g-1 together with 92.09% retention after 10,000 cycles at 10 A g-1. More impressively, the zinc-ion hybrid supercapacitor using CSAC as a cathode achieves a high-rate capability (153 mAh g-1 at 0.2 A g-1 and 75 mAh g-1 at 10 A g-1), high energy density (134.9 Wh kg-1 at 175 W kg-1), as well as exceptional cycling stability (93.81% capacity retention after 10,000 cycles at 10 A g-1). Such work thus illuminates a new pathway for converting biowaste-derived carbons into materials for ultrahigh-performance energy storge applications.

Construction of WO3 quantum dots/TiO2 nanowire arrays type II heterojunction via electrostatic self-assembly for efficient solar-driven photoelectrochemical water splitting.

Construction of a heterojunction between quantum dots and TiO2 nanowire arrays via electrostatic self-assembly is rarely reported. In this work, mercury lamp irradiation was used to change the surface potential of WO3 quantum dots and TiO2 nanowire arrays, resulting in WO3 quantum dots tightly attached on the surface of TiO2 nanowire through electrostatic self-assembly. Photoelectrochemical measurements showed that the WO3 quantum dots formed a type II heterojunction with the TiO2 nanowire arrays rather than serving as carrier-trapping sites. In the self-assembly system, the TiO2 nanowire arrays provide a charge-transfer channel for the WO3 quantum dots, greatly improving the contribution of the WO3 quantum dots to the photocurrent. Quantitative calculations showed that the improvement of the bulk carrier-separation efficiency was the reason for the enhanced photoelectrochemical performance of the self-assembled system. The photocurrent density of the optical self-assembled system at 1.23 V (vs. RHE) was ∼5.5 times as high as that of the TiO2 nanowire arrays. More importantly, the self-assembled system exhibited excellent photoelectrochemical stability.

Synergistic effects of the Rh-S bond and spatially separated dual cocatalysts on photocatalytic overall water splitting activity of ZnIn2S4 nanosheets under visible light irradiation.

Photodeposition of dual-cocatalysts Pt-Cr or Rh-Cr on the surface of ZnIn2S4 is used to achieve overall water splitting. Compared with the hybrid loading of the Pt element and Cr element, the formation of the Rh-S bond results in space separation of the Rh element and Cr element. The Rh-S bond and space separation of cocatalysts promote the transfer of bulk carriers to the surface and inhibit self-corrosion.

Facile Chemical Vapor Modification Strategy to Construct Surface Cyano-Rich Polymer Carbon Nitrides for Highly Efficient Photocatalytic H2 Evolution.

The surface grafting of electro-negative cyano groups on polymer carbon nitrides (PCNs) is an effective way to tail their electronic structure. Despite the significant progress in the synthesis of cyano group-enriched PCN, developing a simple and efficient method remains challenging. Here, a facile strategy was developed for fabricating surface cyano-rich PCN (PCN-DM) with a porous structure via chemical vapor modification using diaminomaleonitrile. The cyano groups of diaminomaleonitrile substituted the amino groups on PCN surface via a deamination. The hydrogen production rate of the PCN-DM was approximately 17 times higher than that of pristine PCN. This significant increase in photocatalytic performance could be assigned to the fusion of cyano groups in the surface of PCN, forming new gap states that broadened the visible-light harvesting and accelerated charge separation for photoredox reactions. This study unveils a promising approach for incorporating functional units in the design of novel photocatalysts for efficient hydrogen production.

Stable and efficient solar-driven photoelectrochemical water splitting into H2 and O2 based on a BaTaO2N photoanode decorated with CoO microflowers.

Stable and efficient photoelectrochemical water splitting has been achieved using a BaTaO2N photoanode decorated with CoO microflowers. The CoO microflowers effectively collect holes from BaTaO2N which kinetically protects BaTaO2N against photocorrosion. A Faraday efficiency of almost unity (99.2%) has been recorded for O2 evolution reactions. The tips of the CoO microflowers are the most active sites for water oxidation reactions.

Selective Cocatalyst Deposition on ZnTiO3-x Ny Hollow Nanospheres with Efficient Charge Separation for Solar-Driven Overall Water Splitting.

Pt and RhOx cocatalysts are selectively deposited at inner and outer surface of ZnTiO3-x Ny hollow nanospheres, respectively. The resulting photocatalytic systems exhibit promising activity for photocatalytic overall water splitting with stoichiometric H2 /O2 ratio under simulated solar insolation. Selective deposition of Pt and RhOx cocatalysts at different surfaces not only mitigates back reactions of the products but also induces strong potential gradient within nanospheres that promotes efficient dissociation and fast migration of photocarriers to the surface.

Enhanced photocatalytic hydrogen production of MoS2 sheet/carbon nanofiber using rapid electron transport of Mo6+ and carbon nanofiber.

Normal MoS2 exhibits a low photocatalytic performance for H2 production owing to the deficiency of the active sites and the poor electrical conductance. In this work, MoS2 anchored on the surface of the carbon nanofibers was designed to enhance the activity of the exposed edge and the electrical conductivity at the same time. The oxidation of the surface Mo atoms increases the activity of the exposed edge of the MoS2. The introduction of carbon nanofibers facilitates the effective transportation of the electron-hole pairs by enhancing the electrical conductivity. As a result, the introduction of carbon nanofibers and Mo6+ can facilitate the electron-hole pair separation to enhance the photocatalytic hydrogen evolution reaction (HER) performance (to eight fold more than normal MoS2).

Ultrathin Lanthanum Tantalate Perovskite Nanosheets Modified by Nitrogen Doping for Efficient Photocatalytic Water Splitting.

Ultrathin nitrogen-doped perovskite nanosheets LaTa2O6.77N0.15- have been fabricated by exfoliating Dion-Jacobson-type layered perovskite RbLaTa2O6.77N0.15. These nanosheets demonstrate superior photocatalytic activities for water splitting into hydrogen and oxygen and remain active with photon wavelengths as far as 600 nm. Their apparent quantum efficiency under visible-light illumination (λ ≥ 420 nm) approaches 1.29% and 3.27% for photocatalytic hydrogen and oxygen production, being almost 4-fold and 8-fold higher than bulk RbLaTa2O6.77N0.15. Their outstanding performance likely stems from their tiny thickness (single perovskite slab) that essentially removes bulk charge diffusion steps and extends the lifetime of photogenerated charges. Theoretical calculations reveal a peculiar 2D charge transportation phenomenon in RbLaTa2O6.77N0.15; thus, exfoliating RbLaTa2O6.77N0.15 into LaTa2O6.77N0.15- nanosheets has limited impact on charge transportation properties but significantly enhances the surface areas which contributes to more reaction sites.

Development of High Sensitivity Humidity Sensor Based on Gray TiO2/SrTiO3 Composite.

A gray TiO2/SrTiO3 composite nanocrystalline sensor with narrow band-gap was successfully prepared through a facile wet chemical method. The precursor was calcined in N2 flow under atmospheric pressure and thereafter, a humidity sensor based on the composite was fabricated. The sensor showed high resistive sensitivity and varied by more than four orders of magnitude with an increase in relative humidity (RH) from 11% to 95%. The response and recovery time were about 3.1 s and 76 s, respectively with maximum hysteresis at 1% RH. In comparison with pure SrTiO3 and black TiO2, the gray composite based device exhibits a higher sensitivity. These results demonstrate the potential of gray TiO2/SrTiO3 for humidity sensing applications.

Black and yellow anatase titania formed by (H,N)-doping: strong visible-light absorption and enhanced visible-light photocatalysis.

Black and yellow anatase TiO2 doped with hydrogen and nitrogen elements annealed under a N2/Ar/air atmosphere are produced. More interestingly, one kind of black TiO2 has excellent performance for degradation of methylene blue under visible-light irradiation but photodegradation of the other is quite limited.