The practical application of the Zn‐metal anode for aqueous batteries is greatly restricted by catastrophic dendrite growth, intricate hydrogen evolution, and parasitic surface passivation. Herein, a ...polyanionic hydrogel film is introduced as a protective layer on the Zn anode with the assistance of a silane coupling agent (denoted as Zn–SHn). The hydrogel framework with zincophilic –SO3− functional groups uniformizes the zinc ions flux and transport. Furthermore, such a hydrogel layer chemically bonded on the Zn surface possesses an anti‐catalysis effect, which effectively suppresses both the hydrogen evolution reaction and formation of Zn dendrites. As a result, stable and reversible Zn stripping/plating at various currents and capacities is achieved. A full cell by pairing the Zn–SHn anode with a NaV3O8·1.5 H2O cathode shows a capacity of around 176 mAh g−1 with a retention around 67% over 4000 cycles at 10 A g−1. This polyanionic hydrogel film protection strategy paves a new way for future Zn‐anode design and safe aqueous batteries construction.
A unique polyanionic hydrogel is employed as an artificial protective layer for reversible Zn‐metal anodes. The polyanions in the hydrogel framework facilitate a homogeneous zinc‐ion flux, and the Zn–O bonding strengthens the interface and suppresses surface corrosion and irregular Zn dendrites growth. This strategy could apply also to other aqueous metal batteries.
The gradually increased concentration of carbon dioxide (CO2) in the atmosphere has been recognized as the primary culprit for the rise of the global mean temperature. In recent years, development of ...routes for highly efficient conversion of CO2 has received much attention. This Review describes recent progress on the design and synthesis of solid‐state catalysts for the electrochemical reduction of CO2. The significance of this catalytic conversion is presented, followed by the general parameters for CO2 electroreduction and a summary of the reaction apparatus. We also discuss various types of solid catalysts based on their CO2 conversion mechanisms. We summarize the crucial factors (particle size, surface structure, composition, etc.) determining the performance for electroreduction.
CO2 can do: Electroreduction of CO2 is an important CO2 conversion route because of its high environmental compatibility and good combination with other renewable energy sources. Nanostructured materials exhibit outstanding performances for heterogeneous electrocatalytic CO2 reduction. This Review describes recent advances for these nanostructured heterogeneous catalysts.
A facile photoetching approach is described that alleviates the negative effects from bulk defects by confining the oxygen vacancy (Ovac) at the surface of BiVO4 photoanode, by 10‐minute ...photoetching. This strategy could induce enriched Ovac at the surface of BiVO4, which avoids the formation of excessive bulk defects. A mechanism is proposed to explain the enhanced charge separation at the BiVO4 /electrolyte interface, which is supported by density functional theory (DFT) calculations. The optimized BiVO4 with enriched surface Ovac presents the highest photocurrent among undoped BiVO4 photoanodes. Upon loading FeOOH/NiOOH cocatalysts, photoetched BiVO4 photoanode reaches a considerable water oxidation photocurrent of 3.0 mA cm−2 at 0.6 V vs. reversible hydrogen electrode. An unbiased solar‐to‐hydrogen conversion efficiency of 3.5 % is realized by this BiVO4 photoanode and a Si photocathode under 1 sun illumination.
Surface oxygen vacancies play a significant role in BiVO4 photoanodes during the solar water splitting. Photoetching effectively introduce the surface oxygen vacancies on BiVO4 photoanodes, which enhances the charge separation at the BiVO4/electrolyte interface.
A hundred years on, the energy‐intensive Haber–Bosch process continues to turn the N2 in air into fertilizer, nourishing billions of people while causing pollution and greenhouse gas emissions. The ...urgency of mitigating climate change motivates society to progress toward a more sustainable method for fixing N2 that is based on clean energy. Surface oxygen vacancies (surface Ovac) hold great potential for N2 adsorption and activation, but introducing Ovac on the very surface without affecting bulk properties remains a great challenge. Fine tuning of the surface Ovac by atomic layer deposition is described, forming a thin amorphous TiO2 layer on plasmon‐enhanced rutile TiO2/Au nanorods. Surface Ovac in the outer amorphous TiO2 thin layer promote the adsorption and activation of N2, which facilitates N2 reduction to ammonia by excited electrons from ultraviolet‐light‐driven TiO2 and visible‐light‐driven Au surface plasmons. The findings offer a new approach to N2 photofixation under ambient conditions (that is, room temperature and atmospheric pressure).
Surface oxygen vacancies play a promotional role in the outer amorphous TiO2 (a‐TiO2) thin layer during the adsorption and activation of N2. The process facilitates N2 reduction to ammonia by excited electrons derived from UV‐light‐driven rutile TiO2 nanorod arrays and visible‐light‐driven gold surface plasmons.
Intelligent reflecting surface (IRS) has drawn a lot of attention recently as a promising new solution to achieve high spectral and energy efficiency for future wireless networks. By utilizing ...massive low-cost passive reflecting elements, the wireless propagation environment becomes controllable and thus can be made favorable for improving the communication performance. Prior works on IRS mainly rely on the instantaneous channel state information (I-CSI), which, however, is practically difficult to obtain for IRS-associated links due to its passive operation and large number of reflecting elements. To overcome this difficulty, we propose in this paper a new two-timescale (TTS) transmission protocol to maximize the achievable average sum-rate for an IRS-aided multiuser system under the general correlated Rician channel model. Specifically, the passive IRS phase shifts are first optimized based on the statistical CSI (S-CSI) of all links, which varies much slowly as compared to their I-CSI; while the transmit beamforming/precoding vectors at the access point (AP) are then designed to cater to the I-CSI of the users' effective fading channels with the optimized IRS phase shifts, thus significantly reducing the channel training overhead and passive beamforming design complexity over the existing schemes based on the I-CSI of all channels. Besides, for ease of practical implementation, we consider discrete phase shifts at each reflecting element of the IRS. For the single-user case, an efficient penalty dual decomposition (PDD)-based algorithm is proposed, where the IRS phase shifts are updated in parallel to reduce the computational time. For the multiuser case, we propose a general TTS stochastic successive convex approximation (SSCA) algorithm by constructing a quadratic surrogate of the objective function, which cannot be explicitly expressed in closed-form. Simulation results are presented to validate the effectiveness of our proposed algorithms and evaluate the impact of S-CSI and channel correlation on the system performance.
Supported vanadium oxides are one of the most promising alternative catalysts for propane dehydrogenation (PDH) and efforts have been made to improve its catalytic performance. However, unlike ...Pt‐based catalysts, the nature of the active site and surface structure of the supported vanadium catalysts under reductive reaction conditions still remain elusive. This paper describes the surface structure and the important role of surface‐bound hydroxyl groups on VOx / γ‐Al2O3 catalysts under reaction conditions employing in situ DRIFTS experiments and DFT calculations. It is shown that hydroxyl groups on the VOx /Al2O3 catalyst (V−OH) are produced under H2 pre‐reduction, and the catalytic performance for PDH is closely connected to the concentration of V−OH species on the catalyst. The hydroxyl groups are found to improve the catalyst that leads to better stability by suppressing the coke deposition.
Lending support: The effect of surface hydroxyl groups, on supported vanadium catalysts, on the activity of propane dehydrogenation is studied. Although surface OH groups slightly suppress its dehydrogenation activity, the catalyst stability is increased. DFT calculations confirm that the existence of OH groups block the exposed V3+, on which there is a strong tendency to form coke.
Copper can efficiently electro‐catalyze carbon dioxide reduction to C2+ products (C2H4, C2H5OH, n‐propanol). However, the correlation between the activity and active sites remains ambiguous, impeding ...further improvements in their performance. The facet effect of copper crystals to promote CO adsorption and C−C coupling and consequently yield a superior selectivity for C2+ products is described. We achieve a high Faradaic efficiency (FE) of 87 % and a large partial current density of 217 mA cm−2 toward C2+ products on Cu(OH)2‐D at only −0.54 V versus the reversible hydrogen electrode in a flow‐cell electrolyzer. With further coupled to a Si solar cell, record‐high solar conversion efficiencies of 4.47 % and 6.4 % are achieved for C2H4 and C2+ products, respectively. This study provides an in‐depth understanding of the selective formation of C2+ products on Cu and paves the way for the practical application of electrocatalytic or solar‐driven CO2 reduction.
The facet effect of copper crystals to promote CO adsorption and C−C coupling and consequently yield a superior selectivity (87 % Faradaic efficiency) for C2+ products is described. Record‐high solar conversion efficiencies of 4.47 % and 6.4 % are achieved for C2H4 and C2+ products, respectively.
It is of great significance to reveal the detailed mechanism of neighboring effects between monomers, as they could not only affect the intermediate bonding but also change the reaction pathway. This ...paper describes the electronic effect between neighboring Zn/Co monomers effectively promoting CO2 electroreduction to CO. Zn and Co atoms coordinated on N doped carbon (ZnCoNC) show a CO faradaic efficiency of 93.2 % at −0.5 V versus RHE during a 30‐hours test. Extended X‐ray absorption fine structure measurements (EXAFS) indicated no direct metal–metal bonding and X‐ray absorption near‐edge structure (XANES) showed the electronic effect between Zn/Co monomers. In situ attenuated total reflection‐infrared spectroscopy (ATR‐IR) and density functional theory (DFT) calculations further revealed that the electronic effect between Zn/Co enhanced the *COOH intermediate bonding on Zn sites and thus promoted CO production. This work could act as a promising way to reveal the mechanism of neighboring monomers and to influence catalysis.
The electronic effect between neighboring Zn/Co monomers that effectively enhances the *COOH adsorption and thus boosts CO2 electroreduction to CO is described.
The exploration of highly efficient electrocatalysts for both oxygen and hydrogen generation via water splitting is receiving considerable attention in recent decades. Up till now, Pt‐based catalysts ...still exhibit the best hydrogen evolution reaction (HER) performance and Ir/Ru‐based oxides are identified as the benchmark for oxygen evolution reaction (OER). However, the high cost and rarity of these materials extremely hinder their large‐scale applications. This paper describes the construction of the ultrathin defect‐enriched 3D Se‐(NiCo)Sx/(OH)x nanosheets for overall water splitting through a facile Se‐induced hydrothermal treatment. Via Se‐induced fabrication, highly efficient Se‐(NiCo)Sx/(OH)x nanosheets are successfully fabricated through morphology optimization, defect engineering, and electronic structure tailoring. The as‐prepared hybrids exhibit relatively low overpotentials of 155 and 103 mV at the current density of 10 mA cm−2 for OER and HER, respectively. Moreover, an overall water‐splitting device delivers a current density of 10 mA cm−2 for ≈66 h without obvious degradation.
The construction of ultrathin defectenriched Se‐(NiCo)Sx/(OH)x nanosheets through a facile Se‐induced hydrothermal treatment is described. Benefiting from morphological optimization, defect engineering, and tailoring of the electronic structure, Se‐(NiCo)Sx/(OH)x exhibits highly efficient activity and long‐term stability for oxygen evolution, hydrogen evolution, and overall water splitting.
Chirp waveform plays a significant role in radar and communication systems for its ability of pulse compression and spread spectrum. This paper presents a principle of multiplexing a bank of ...orthogonal chirps, termed orthogonal chirp-division multiplexing (OCDM) for high-speed communication. As Fourier transform is the kernel of orthogonal frequency-division multiplexing (OFDM), which achieves the maximum spectral efficiency (SE) of frequency-division multiplexing, Fresnel transform underlies the proposed OCDM system, which achieves the maximum SE of chirp spread spectrum. By using discrete Fresnel transform, digital implementation of OCDM is introduced. According to the properties of Fresnel transform, the transmission of OCDM signal in linear time-invariant channel is studied. Efficient digital signal processing is proposed for channel dispersion compensation. The implementation of the OCDM system is discussed with the emphasis on its compatibility to the OFDM system; it is shown that it can be easily integrated into the existing OFDM systems. Finally, the simulations are provided to validate the feasibility of the proposed OCDM. It is shown that the OCDM system can efficiently exploit multipath diversity and thus outperforms the OFDM, and that it is more resilient against the interference due to insufficient guard interval than single-carrier frequency-domain equalization.
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