9 research outputs found
Enhanced solar evaporation of water from porous media, through capillary mediated forces and surface treatment
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<p>The relative influence of the capillary, Marangoni, and hydrophobic forces in mediating the evaporation of water from carbon foam based porous media, in response
to incident solar radiation, are investigated. It is indicated that inducing hydrophilic
interactions on the surface, through nitric acid treatment of the foams, has a similar
effect to reduced pore diameter and the ensuing capillary forces. The efficiency of
water evaporation may be parameterized through the Capillary number (Ca), with
a lower Ca being preferred. The proposed study is of much relevance to efficient
solar energy utilization. Â </p>
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Lithiation of Rutile TiO<sub>2</sub>‑Coated Si NWs Observed by in Situ TEM
Lithiation of Rutile TiO<sub>2</sub>‑Coated
Si NWs Observed by in Situ TE
Lithiation of Rutile TiO<sub>2</sub>‑Coated Si NWs Observed by in Situ TEM
Lithiation of Rutile TiO<sub>2</sub>‑Coated
Si NWs Observed by in Situ TE
ZnO/CuO Heterojunction Branched Nanowires for Photoelectrochemical Hydrogen Generation
We report a facile and large-scale fabrication of three-dimensional (3D) ZnO/CuO heterojunction branched nanowires (b-NWs) and their application as photocathodes for photoelectrochemical (PEC) solar hydrogen production in a neutral medium. Using simple, cost-effective thermal oxidation and hydrothermal growth methods, ZnO/CuO b-NWs are grown on copper film or mesh substrates with various ZnO and CuO NWs sizes and densities. The ZnO/CuO b-NWs are characterized in detail using high-resolution scanning and transmission electron microscopies exhibiting single-crystalline defect-free b-NWs with smooth and clean surfaces. The correlation between electrode currents and different NWs sizes and densities are studied in which b-NWs with longer and denser CuO NW cores show higher photocathodic current due to enhanced reaction surface area. The ZnO/CuO b-NW photoelectrodes exhibit broadband photoresponse from UV to near IR region, and higher photocathodic current than the ZnO-coated CuO (core/shell) NWs due to improved surface area and enhanced gas evolution. Significant improvement in the photocathodic current is observed when ZnO/CuO b-NWs are grown on copper mesh compared to copper film. The achieved results offer very useful guidelines in designing b-NWs mesh photoelectrodes for high-efficiency, low-cost, and flexible PEC cells using cheap, earth-abundant materials for clean solar hydrogen generation at large scales
3D Branched Nanowire Photoelectrochemical Electrodes for Efficient Solar Water Splitting
We report the systematic study of 3D ZnO/Si branched nanowire (b-NW) photoelectrodes and their application in solar water splitting. We focus our study on the correlation between the electrode design and structures (including Si NW doping, dimension of the trunk Si and branch ZnO NWs, and b-NW pitch size) and their photoelectrochemical (PEC) performances (efficiency and stability) under neutral conditions. Specifically, we show that for b-NW electrodes with lightly doped p-Si NW core, larger ZnO NW branches and longer Si NW cores give a higher <i>photocathodic</i> current, while for b-NWs with heavily doped p-Si NW trunks smaller ZnO NWs and shorter Si NWs provide a higher <i>photoanodic</i> current. Interestingly, the photocurrent turn-on potential decreases with longer p-Si NW trunks and larger ZnO NW branches resulting in a significant photocathodic turn-on potential shift of ∼600 mV for the optimized ZnO/p-Si b-NWs compared to that of the bare p-Si NWs. A photocathode energy conversion efficiency of greater than 2% at −1 V <i>versus</i> Pt counter electrode and in neutral solution is achieved for the optimized ZnO/p-Si b-NW electrodes. The PEC performances or incident photon-to-current efficiency are further improved using Si NW cores with smaller pitch size. The photoelectrode stability is dramatically improved by coating a thin TiO<sub>2</sub> protection layer using atomic-layer deposition method. These results provide very useful guidelines in designing photoelectrodes for selective solar water oxidation/reduction and overall spontaneous solar fuel generation using low cost earth-abundant materials for practical clean solar fuel production
Solution-Processed CoFe<sub>2</sub>O<sub>4</sub> Nanoparticles on 3D Carbon Fiber Papers for Durable Oxygen Evolution Reaction
We report CoFe<sub>2</sub>O<sub>4</sub> nanoparticles (NPs) synthesized using a facile hydrothermal growth
and their attachment on 3D carbon fiber papers (CFPs) for efficient
and durable oxygen evolution reaction (OER). The CFPs covered with
CoFe<sub>2</sub>O<sub>4</sub> NPs show orders of magnitude higher
OER performance than bare CFP due to high activity of CoFe<sub>2</sub>O<sub>4</sub> NPs, leading to a small overpotential of 378 mV to
get a current density of 10 mA/cm<sup>2</sup>. Significantly, the
CoFe<sub>2</sub>O<sub>4</sub> NPs-on-CFP electrodes exhibit remarkably
long stability evaluated by continuous cycling (over 15 h) and operation
with a high current density at a fixed potential (over 40 h) without
any morphological change and with preservation of all materials within
the electrode. Furthermore, the CoFe<sub>2</sub>O<sub>4</sub> NPs-on-CFP
electrodes also exhibit hydrogen evolution reaction (HER) performance,
which is considerably higher than that of bare CFP, acting as a bifunctional
electrocatalyst. The achieved results show promising potential for
efficient, cost-effective, and durable hydrogen generation at large
scales using earth-abundant materials and cheap fabrication processes
Solution-Processed CoFe<sub>2</sub>O<sub>4</sub> Nanoparticles on 3D Carbon Fiber Papers for Durable Oxygen Evolution Reaction
We report CoFe<sub>2</sub>O<sub>4</sub> nanoparticles (NPs) synthesized using a facile hydrothermal growth
and their attachment on 3D carbon fiber papers (CFPs) for efficient
and durable oxygen evolution reaction (OER). The CFPs covered with
CoFe<sub>2</sub>O<sub>4</sub> NPs show orders of magnitude higher
OER performance than bare CFP due to high activity of CoFe<sub>2</sub>O<sub>4</sub> NPs, leading to a small overpotential of 378 mV to
get a current density of 10 mA/cm<sup>2</sup>. Significantly, the
CoFe<sub>2</sub>O<sub>4</sub> NPs-on-CFP electrodes exhibit remarkably
long stability evaluated by continuous cycling (over 15 h) and operation
with a high current density at a fixed potential (over 40 h) without
any morphological change and with preservation of all materials within
the electrode. Furthermore, the CoFe<sub>2</sub>O<sub>4</sub> NPs-on-CFP
electrodes also exhibit hydrogen evolution reaction (HER) performance,
which is considerably higher than that of bare CFP, acting as a bifunctional
electrocatalyst. The achieved results show promising potential for
efficient, cost-effective, and durable hydrogen generation at large
scales using earth-abundant materials and cheap fabrication processes
High-Performance <i>a</i>‑Si/c-Si Heterojunction Photoelectrodes for Photoelectrochemical Oxygen and Hydrogen Evolution
Amorphous Si (<i>a</i>-Si)/crystalline
Si (c-Si) heterojunction (SiHJ) can serve as highly efficient and
robust photoelectrodes for solar fuel generation. Low carrier recombination
in the photoelectrodes leads to high photocurrents and photovoltages.
The SiHJ was designed and fabricated into both photoanode and photocathode
with high oxygen and hydrogen evolution efficiency, respectively,
by simply coating of a thin layer of catalytic materials. The SiHJ
photoanode with sol–gel NiO<sub><i>x</i></sub> as
the catalyst shows a current density of 21.48 mA/cm<sup>2</sup> at
the equilibrium water oxidation potential. The SiHJ photocathode with
2 nm sputter-coated Pt catalyst displays excellent hydrogen evolution
performance with an onset potential of 0.640 V and a solar to hydrogen
conversion efficiency of 13.26%, which is the highest ever reported
for Si-based photocathodes
Tailoring n‑ZnO/p-Si Branched Nanowire Heterostructures for Selective Photoelectrochemical Water Oxidation or Reduction
We
report the fabrication of three-dimensional (3D) branched nanowire
(NW) heterostructures, consisting of periodically ordered vertical
Si NW trunks and ZnO NW branches, and their application for solar
water splitting. The branched NW photoelectrodes show orders of magnitudes
higher photocurrent compared to the bare Si NW electrodes. More interestingly,
selective photoelectrochemical cathodic or anodic behavior resulting
in either solar water oxidation or reduction was achieved by tuning
the doping concentration of the p-type Si NW core. Specifically, n-ZnO/p-Si
branched NW array electrodes with lightly doped core show broadband
absorption from UV to near IR region and photocathodic water reduction,
while n-ZnO/p<sup>+</sup>-Si branched NW arrays show photoanodic water
oxidation with photoresponse only to UV light. The photoelectrochemical
stability for over 24 h under constant light illumination and fixed
biasing potential was achieved by coating the branched NW array with
thin layers of TiO<sub>2</sub> and Pt. These studies not only reveal
the promise of 3D branched NW photoelectrodes for high efficiency
solar energy harvesting and conversion to clean chemical fuels, but
also developing understanding enabling rational design of high efficiency
robust photocathodes and photoanodes from low-cost and earth-abundant
materials allowing practical applications in clean renewable energy