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1. Nanostructured core–shell metal borides–oxides as highly efficient electrocatalysts for photoelectrochemical water oxidation

   https://doi.org/10.1039/c9nr09818f  

   Lu, Can ; Jothi, Palani R. ; Thersleff, Thomas ; Budnyak, Tetyana M. ; Rokicinska, Anna ; Yubuta, Kunio ; Dronskowski, Richard ; Kuśtrowski, Piotr ; Fokwa, Boniface P. ; Slabon, Adam ( February 2020 , Nanoscale)

   null (Ed.)

   Oxygen evolution reaction (OER) catalysts are critical components of photoanodes for photoelectrochemical (PEC) water oxidation. Herein, nanostructured metal boride MB (M = Co, Fe) electrocatalysts, which have been synthesized by a Sn/SnCl 2 redox assisted solid-state method, were integrated with WO 3 thin films to build heterojunction photoanodes. As-obtained MB modified WO 3 photoanodes exhibit enhanced charge carrier transport, amended separation of photogenerated electrons and holes, prolonged hole lifetime and increased charge carrier density. Surface modification of CoB and FeB significantly enhances the photocurrent density of WO 3 photoanodes from 0.53 to 0.83 and 0.85 mA cm −2 , respectively, in transient chronoamperometry (CA) at 1.23 V vs. RHE (V RHE ) under interrupted illumination in 0.1 M Na 2 SO 4 electrolyte (pH 7), corresponding to an increase of 1.6 relative to pristine WO 3 . In contrast, the pristine MB thin film electrodes do not produce noticeable photocurrent during water oxidation. The metal boride catalysts transform in situ to a core–shell structure with a metal boride core and a metal oxide (MO, M = Co, Fe) surface layer. When coupled to WO 3 thin films, the CoB@CoO x nanostructures exhibit a higher catalytic enhancement than corresponding pure cobalt borate (Co-B i ) and cobalt hydroxide (Co(OH) x ) electrocatalysts. Our results emphasize the role of the semiconductor–electrocatalyst interface for photoelectrodes and their high dependency on materials combination. 

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2. Scalable Core–Shell MoS 2 /Sb 2 Se 3 Nanorod Array Photocathodes for Enhanced Photoelectrochemical Water Splitting

   https://doi.org/10.1002/solr.201900442  

   Guo, Liping ; Shinde, Pravin S. ; Ma, Yanxiao ; Li, Lin ; Pan, Shanlin ; Yan, Feng ( November 2019 , Solar RRL)

   Photoelectrochemical (PEC) hydrogen generation is a promising solar energy harvesting technique to address the concerns about the ongoing energy crisis. Antimony selenide (Sb₂Se₃) with van der Waals‐bonded quasi‐1D (Q1D) nanoribbons, for instance, (Sb₄Se₆)_n, has attracted considerable interest as a light absorber with Earth‐abundant elements, suitable bandgap, and a desired sunlight absorption coefficient. By tuning its anisotropic growth behavior, it is possible to achieve Sb₂Se₃films with nanostructured morphologies that can improve the light absorption and photogenerated charge carrier separation, eventually boosting the PEC water‐splitting performance. Herein, high‐quality Sb₂Se₃films with nanorod (NR) array surface morphologies are synthesized by a low‐cost, high‐yield, and scalable close‐spaced sublimation technique. By sputtering a nonprecious and scalable crystalline molybdenum sulfide (MoS₂) film as a cocatalyst and a protective layer on Sb₂Se₃NR arrays, the fabricated core–shell structured MoS₂/Sb₂Se₃NR PEC devices can achieve a photocurrent density as high as −10 mA cm⁻²at 0 V_RHEin a buffered near‐neutral solution (pH 6.5) under a standard simulated air mass 1.5 solar illumination. The scalable manufacturing of nanostructured MoS₂/Sb₂Se₃NR array thin‐film photocathode electrodes for efficient PEC water splitting to generate solar fuel is demonstrated.

    

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3. Simultaneous Enhancement of Charge Separation and Hole Transportation in a TiO 2 –SrTiO 3 Core–Shell Nanowire Photoelectrochemical System

   https://doi.org/10.1002/adma.201701432  

   Wu, Fei ; Yu, Yanhao ; Yang, Huang ; German, Lazarus N. ; Li, Zhenquan ; Chen, Jianguo ; Yang, Weiguang ; Huang, Lu ; Shi, Weimin ; Wang, Linjun ; et al ( May 2017 , Advanced Materials)

   Efficient charge separation and transportation are key factors that determine the photoelectrochemical (PEC) water‐splitting efficiency. Here, a simultaneous enhancement of charge separation and hole transportation on the basis of ferroelectric polarization in TiO₂–SrTiO₃core–shell nanowires (NWs) is reported. The SrTiO₃shell with controllable thicknesses generates a considerable spontaneous polarization, which effectively tunes the electrical band bending of TiO₂. Combined with its intrinsically high charge mobility, the ferroelectric SrTiO₃thin shell significantly improves the charge‐separation efficiency (η_separation) with minimized influence on the hole‐migration property of TiO₂photoelectrodes, leading to a drastically increased photocurrent density (J_ph). Specifically, the 10 nm‐thick SrTiO₃shell yields the highestJ_phand η_separationof 1.43 mA cm⁻²and 87.7% at 1.23 V versus reversible hydrogen electrode, respectively, corresponding to 83% and 79% improvements compared with those of pristine TiO₂NWs. The PEC performance can be further manipulated by thermal treatment, and the control of SrTiO₃film thicknesses and electric poling directions. This work suggests a material with combined ferroelectric and semiconducting features could be a promising solution for advancing PEC systems by concurrently promoting the charge‐separation and hole‐transportation properties.

    

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4. Surface‐Plasmon‐Assisted Photoelectrochemical Reduction of CO 2 and NO 3 − on Nanostructured Silver Electrodes

   https://doi.org/10.1002/aenm.201800363  

   Kim, Youngsang ; Creel, Erin B. ; Corson, Elizabeth R. ; McCloskey, Bryan D. ; Urban, Jeffrey J. ; Kostecki, Robert ( May 2018 , Advanced Energy Materials)

   Electrochemical reduction of carbon dioxide (CO₂) typically suffers from low selectivity and poor reaction rates that necessitate high overpotentials, which impede its possible application for CO₂capture, sequestration, or carbon‐based fuel production. New strategies to address these issues include the utilization of photoexcited charge carriers to overcome activation barriers for reactions that produce desirable products. This study demonstrates surface‐plasmon‐enhanced photoelectrochemical reduction of CO₂and nitrate (NO₃⁻) on silver nanostructured electrodes. The observed photocurrent likely originates from a resonant charge transfer between the photogenerated plasmonic hot electrons and the lowest unoccupied molecular orbital (MO) acceptor energy levels of adsorbed CO₂, NO₃⁻, or their reductive intermediates. The observed differences in the resonant effects at the Ag electrode with respect to electrode potential and photon energy for CO₂versus NO₃⁻reduction suggest that plasmonic hot‐carriers interact selectively with specific MO acceptor energy levels of adsorbed surface species such as CO₂, NO₃⁻, or their reductive intermediates. This unique plasmon‐assisted charge generation and transfer mechanism can be used to increase yield, efficiency, and selectivity of various photoelectrochemical processes.

    

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5. Chemical composition tuning induced variable and enhanced dielectric properties of polycrystalline Ga2‐2xWxO3 ceramics

   https://doi.org/10.1002/eng2.12300  

   Zade, Vishal B. ; Rajkumar, Mohan R. ; Broner, Ron ; Ramana, Chintalapalle V. ( December 2020 , Engineering Reports)

   We report on the tunable and enhanced dielectric properties of tungsten (W) incorporated gallium oxide (Ga₂O₃) polycrystalline electroceramics for energy and power electronic device applications. The W‐incorporated Ga₂O₃(Ga_2−2xW_xO₃, 0.00 ≤ x ≤ 0.20; GWO) compounds were synthesized by the high‐temperature solid‐state chemical reaction method by varying the W‐content. The fundamental aspects of the dielectric properties in correlation with the crystal structure, phase, and microstructure of the GWO polycrystalline compounds has been investigated in detail. A detailed study performed ascertains the W‐induced changes in the dielectric constant, loss tangent (tanδ) and ac conductivity. It was found that the dielectric constant increases with addition of W in the system as a function of temperature (25°C‐500°C). Frequency dependence (10²‐10⁶ Hz) of the dielectric constant follows the modified Debye model with a relaxation time of ∼20 to 90 μs and a spreading factor of 0.39 to 0.65. The dielectric constant of GWO is temperature independent almost until ∼300°C, and then increases rapidly in the range of 300°C to 500°C. W‐induced enhancement in the dielectric constant of GWO is fully evident in the frequency and temperature dependent dielectric studies. The frequency and temperature dependent tanδreveals the typical behavior of relaxation loses in GWO. Small polaron hopping mechanism is evident in the frequency dependent electrical transport properties of GWO. The remarkable effect of W‐incorporation on the dielectric and electrical transport properties of Ga₂O₃is explained by a two‐layer heterogeneous model consisting of thick grains separated by very thin grain boundaries along with the formation of a Ga₂O₃‐WO₃composite was able to account for the observed temperature and frequency dependent electrical properties in GWO. The results demonstrate that the structure, electrical and dielectric properties can be tailored by tuning W‐content in the GWO compounds.

    

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