production of pure H 2 ; this technique can be coupled with other instantaneous energy conversion techniques. [2] However, the sluggish reaction kinetics of both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) limit the application of water splitting. [3] So far, ruthenium-(Ru-), iridium-(Ir-), and platinum-(Pt-) based materials, such as noble metal oxides, [4] noble-metal single-atom catalysts, [5] and hetero-structured noblemetal-based catalysts [6] are still the most efficient HER and OER catalysts. However, their high costs and low stability greatly limit their practical application. Great efforts has been devoted to exploring novel inexpensive bifunctional catalysts for efficient overall water splitting. [7] In particular, the development of non-noble-metal-based catalysts under alkaline conditions, which require several-fold high catalytic activity due to the ultralow proton activity in alkaline solution, was found to be an attractive but challenging approach. [8] Dispersing ultralow-content noble metals on nonprecious material platforms is an effective improvement strategy. This approach not only improves the adsorption capabilities of hydrogen-and oxygencontaining intermediates and accelerates the reaction kinetics of both the HER and OER, [9] but also balances the performance and cost. Multimetal-based layered double hydroxides (LDHs) can be utilized as support materials owing to their low cost, Rational exploration of efficient, inexpensive, and robust electrocatalysts is critical for the efficient water splitting. Conjugated conductive metal-organic frameworks (cMOFs) with multicomponent layered double hydroxides (LDHs) to construct bifunctional heterostructure catalysts are considered as an efficient but complicated strategy. Here, the fabrication of a cMOF/ LDH hetero-nanotree array catalyst (CoNiRu-NT) coupled with monodispersed ruthenium (Ru) sites via a controllable grafted-growth strategy is reported. Rich-amino hexaiminotriphenylene linkers coordinate with the LDH nanotrunk to form cMOF nanobranches, providing numerous anchoring sites to precisely confine and stabilize RuN 4 sites. Moreover, mono dispersed and reduced Ru moieties facilitate H 2 O adsorption and dissociation, and the heterointerface between the cMOF and the LDH further modifies the chemical and electronic structures. Optimized CoNiRu-NT displays a significant increase in electrochemical water-splitting properties in alkaline media, affording low overpotentials of 22 mV at 10 mA cm −2 and 255 mV at 20 mA cm −2 for the hydrogen evolution reaction and oxygen evolution reaction, respectively. In an actual electrochemical system, CoNiRu-NT drives an overall water splitting at a low cell voltage of 1.47 V to reach 10 mA cm −2 . This performance is comparable to that of pure noble-metal-based materials and superior to most reported MOF-based catalysts.
Functionalized graphene dots attract glucose for effective photocatalytic reforming of glucose into H2 under visible light irradiation.
This paper presents a heteroatom doping strategy to manipulate the structure of graphene-based photocatalysts for effective hydrogen production from aqueous solution. Oxygenation of graphene creates a bandgap to produce semiconducting graphene oxide, nitrogen doping extends the resonant π-conjugation to prolong the charge lifetime, and sulfur doping breaks the electron neutrality to facilitate charge transfer. Accordingly, ammonia-treated sulfur-nitrogen-co-doped graphene oxide dots (A-SNGODs) are synthesized by annealing graphene oxide sheets in sulfur-ammonia, oxidizing the sheets into dots, and then hydrothermally treating the dots in ammonia. The A-SNGODs exhibit a high nitrogen content in terms of quaternary and amide groups that are formed through sulfur-mediated reactions. The peripheral amide facilitates orbital conjugations to enhance the photocatalytic activity, whereas the quaternary nitrogen patches vacancy defects to improve stability. The simultaneous presence of electron-withdrawing S and electron-donating N atoms in the A-SNGODs facilitates charge separation and results in reactive electrons. When suspended in an aqueous triethanolamine solution, Pt-deposited A-SNGODs demonstrate a hydrogen-evolution quantum yield of 29% under monochromatic 420 nm irradiation. The A-SNGODs exhibit little activity decay under 6-day visible-light irradiation. This study demonstrates the excellence of the heteroatom-doping strategy in producing stable and active graphene-based materials for photoenergy conversion.
The flexible triboelectric nanogenerator (TENG) has promising applications in portable electronic devices and micro wireless sensors. However, complex fabrication processes, high cost, and difficulty in coupling with the human body are still the challenges for the further development of TENG. Herein, a flexible double‐sided patterned titanium nitride/polydimethylsiloxane (DSP‐TiN/PDMS) composite film is prepared by a simple and low‐cost sandpaper template method. The double‐sided microporous structure on the PDMS increases the effective contact area and promotes more charge storage on the PDMS surface, thus improving the output performance of TENG. With the introduction of conductive TiN nanoparticles, the effective thickness of the composite film can be reduced, leading to the increase of the capacitance value of TENG. Therefore, the TENG fabricated under the conditions of optimized filling content and surface patterning microstructure can generate a high open‐circuit voltage of 51.8 V and a short‐circuit current of 36.8 μA, as well as a peak power of 11.25 μW. Furthermore, the proposed TENG can also achieve effective energy harvesting in human motions. This easy‐to‐prepare DSP‐TiN/PDMS composite film opens up a feasible way for the construction of high output performance TENG and presents promising applications in micro wearable devices.
The synergy between quantum confinement and chemical functionality in graphene-dot media produces high quantum yields in photocatalytic H2 evolution.
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