Controlled Sn-Doping in TiO₂ Nanowire Photoanodes with Enhanced Photoelectrochemical Conversion

We demonstrate for the first time the controlled Sn-doping in TiO₂ nanowire (NW) arrays for photoelectrochemical (PEC) water splitting. Because of the low lattice mismatch between SnO₂ and TiO₂, Sn dopants are incorporated into TiO₂ NWs by a one-pot hydrothermal synthesis with different ratios of SnCl₄ and tetrabutyl titanate, and a high acidity of the reactant solution is critical to control the SnCl₄ hydrolysis rate. The obtained Sn-doped TiO₂ (Sn/TiO₂) NWs are single crystalline with a rutile structure, and the incorporation of Sn in TiO₂ NWs is well controlled at a low level, that is, 1–2% of Sn/Ti ratio, to avoid phase separation or interface scattering. PEC measurement on Sn/TiO₂ NW photoanodes with different Sn doping ratios shows that the photocurrent increases first with increased Sn doping level to >2.0 mA/cm² at 0 V vs Ag/AgCl under 100 mW/cm² simulated sunlight illumination up to ∼100% enhancement compared to our best pristine TiO₂ NW photoanodes and then decreases at higher Sn doping levels. Subsequent annealing of Sn/TiO₂ NWs in H₂ further improves their photoactivity with an optimized photoconversion efficiency of ∼1.2%. The incident-photon-to-current conversion efficiency shows that the photocurrent increase is mainly ascribed to the enhancement of photoactivity in the UV region, and the electrochemical impedance measurement reveals that the density of n-type charge carriers can be significantly increased by the Sn doping. These Sn/TiO₂ NW photoanodes are highly stable in PEC conversion and thus can serve as a potential candidate for pure TiO₂ materials in a variety of solar energy driven applications

All-Nanowire Based Li-Ion Full Cells Using Homologous Mn₂O₃ and LiMn₂O₄

We report an all-nanowire based flexible Li-ion battery full cell, using homologous Mn₂O₃ and LiMn₂O₄ nanowires for anodes and cathodes, respectively. The same precursors, MnOOH nanowires, are transformed from hydrothermally grown MnO₂ nanoflakes and directly attached on Ti foils via reaction with poly­(vinyl pyrrolidone). The Mn₂O₃ anode and LiMn₂O₄ cathode are subsequently formed by thermal annealing and reaction with lithium salt, respectively. The one-dimensional nanowire structures provide short lithium-ion diffusion path, good charge transport, and volume flexibility for Li⁺ intercalation/deintercalation, thus leading to good rate capability and cycling performance. As proof-of-concept, the Mn₂O₃ nanowire anode delivers an initial discharge capacity of 815.9 mA h g^–1 at 100 mA g^–1 and maintains a capacity of 502.3 mA h g^–1 after 100 cycles. The LiMn₂O₄ nanowire cathodes show a reversible capacity of 94.7 mA h g^–1 at 100 mA g^–1 and high capacity retention of ∼96% after 100 cycles. Furthermore, a flexible Mn₂O₃//LiMn₂O₄ lithium ion full cell is fabricated, with an output voltage of >3 V, low thickness of 0.3 mm, high flexibility, and a specific capacity of 99 mA h g^–1 based on the total weight of the cathode material. It also exhibits good cycling stability with a capacity of ∼80 mA h g^–1 after 40 charge/discharge cycles

Automated in Vivo Nanosensing of Breath-Borne Protein Biomarkers

Toxicology and bedside medical condition monitoring is often desired to be both ultrasensitive and noninvasive. However, current biomarker analyses for these purposes are mostly offline and fail to detect low marker quantities. Here, we report a system called dLABer (detection of living animal’s exhaled breath biomarker) that integrates living rats, breath sampling, microfluidics, and biosensors for the automated tracking of breath-borne biomarkers. Our data show that dLABer could selectively detect (online) and report differences (of up to 10³-fold) in the levels of inflammation agent interleukin-6 (IL-6) exhaled by rats injected with different ambient particulate matter (PM). The dLABer system was further shown to have an up to 10⁴ higher signal-to-noise ratio than that of the enzyme-linked immunosorbent assay (ELISA) when analyzing the same breath samples. In addition, both blood-borne IL-6 levels analyzed via ELISA in rats injected with different PM extracts and PM toxicity determined by a dithiothreitol (DTT) assay agreed well with those determined by the dLABer system. Video recordings further verified that rats exposed to PM with higher toxicity (according to a DTT assay and as revealed by dLABer) appeared to be less physically active. All the data presented here suggest that the dLABer system is capable of real-time, noninvasive monitoring of breath-borne biomarkers with ultrasensitivity. The dLABer system is expected to revolutionize pollutant health effect studies and bedside disease diagnosis as well as physiological condition monitoring at the single-protein level

Single-Atomic Cu with Multiple Oxygen Vacancies on Ceria for Electrocatalytic CO₂ Reduction to CH₄

The electrocatalytic reduction of CO₂ into value-added chemicals such as hydrocarbons has the potential for supplying fuel energy and reducing environmental hazards, while the accurate tuning of electrocatalysts at the ultimate single-atomic level remains extremely challenging. In this work, we demonstrate an atomic design of multiple oxygen vacancy-bound, single-atomic Cu-substituted CeO₂ to optimize the CO₂ electrocatalytic reduction to CH₄. We carried out theoretical calculations to predict that the single-atomic Cu substitution in CeO₂(110) surface can stably enrich up to three oxygen vacancies around each Cu site, yielding a highly effective catalytic center for CO₂ adsorption and activation. This theoretical prediction is consistent with our controlled synthesis of the Cu-doped, mesoporous CeO₂ nanorods. Structural characterizations indicate that the low concentration (<5%) Cu species in CeO₂ nanorods are highly dispersed at single-atomic level with an unconventionally low coordination number ∼5, suggesting the direct association of 3 oxygen vacancies with each Cu ion on surfaces. This multiple oxygen vacancy-bound, single atomic Cu-substituted CeO₂ enables an excellent electrocatalytic selectivity in reducing CO₂ to methane with a faradaic efficiency as high as 58%, suggesting strong capabilities of rational design of electrocatalyst active centers for boosting activity and selectivity

Automated in Vivo Nanosensing of Breath-Borne Protein Biomarkers

Toxicology and bedside medical condition monitoring is often desired to be both ultrasensitive and noninvasive. However, current biomarker analyses for these purposes are mostly offline and fail to detect low marker quantities. Here, we report a system called dLABer (detection of living animal’s exhaled breath biomarker) that integrates living rats, breath sampling, microfluidics, and biosensors for the automated tracking of breath-borne biomarkers. Our data show that dLABer could selectively detect (online) and report differences (of up to 10³-fold) in the levels of inflammation agent interleukin-6 (IL-6) exhaled by rats injected with different ambient particulate matter (PM). The dLABer system was further shown to have an up to 10⁴ higher signal-to-noise ratio than that of the enzyme-linked immunosorbent assay (ELISA) when analyzing the same breath samples. In addition, both blood-borne IL-6 levels analyzed via ELISA in rats injected with different PM extracts and PM toxicity determined by a dithiothreitol (DTT) assay agreed well with those determined by the dLABer system. Video recordings further verified that rats exposed to PM with higher toxicity (according to a DTT assay and as revealed by dLABer) appeared to be less physically active. All the data presented here suggest that the dLABer system is capable of real-time, noninvasive monitoring of breath-borne biomarkers with ultrasensitivity. The dLABer system is expected to revolutionize pollutant health effect studies and bedside disease diagnosis as well as physiological condition monitoring at the single-protein level

Surface Plasmon Resonance Enhanced Real-Time Photoelectrochemical Protein Sensing by Gold Nanoparticle-Decorated TiO₂ Nanowires

Recently developed photoelectrochemical (PEC) sensing systems represent a unique potential detection method for real-time analysis of chemical/biological molecules, while the low absorption of TiO₂ nanomaterials in the visible wavelength region and the slow surface charge transfer efficiency limit the ultimate sensitivity. Here we develop a gold nanoparticle-decorated TiO₂ nanowire sensor for PEC detection of protein binding. The direct attachment of Au nanoparticles to TiO₂ nanowires offers strong surface plasmon resonance for electrochemical field effect amplification, yielding a ∼100% increase of photocurrent density. In addition, the surface functionalization of gold nanoparticles allows for direct capturing of target proteins near the Au/TiO₂ interface and thus substantially enhances the capability of attenuation of energy coupling between Au and TiO₂, leading to much-improved sensor performance. As a proof of concept, cholera toxin subunit B has been robustly detected by the TiO₂–Au nanowire sensor functionalized with ganglioside GM1, with a high sensitivity of 0.167 nM and excellent selectivity. Furthermore, the real-time feature of photoelectrochemical sensing enables direct measurement of binding kinetics between cholera toxin subunit B and GM1, yielding association and disassociation rate constants and an equilibrium constant <i>K</i>_d of 4.17 nM. This surface plasmon resonance-enhanced real-time, photoelectrochemical sensing design may lead to exciting biodetection capabilities with high sensitivity and real-time kinetic studies

Weak-Field Electro-Flash Induced Asymmetric Catalytic Sites toward Efficient Solar Hydrogen Peroxide Production

Borocarbonitride (BCN), in a mesoscopic asymmetric state, is regarded as a promising photocatalyst for artificial photosynthesis. However, BCN materials reported in the literature primarily consist of symmetric N-[B]3 units, which generate highly spatial coupled electron–hole pairs upon irradiation, thus kinetically suppressing the solar-to-chemical conversion efficiency. Here, we propose a facile and fast weak-field electro-flash strategy, with which structural symmetry breaking is introduced on key nitrogen sites. As-obtained double-substituted BCN (ds-BCN) possesses high-concentration asymmetric [B]2–N-C coordination, which displays a highly separated electron–hole state and broad visible-light harvesting, as well as provides electron-rich N sites for O2 affinity. Thereby, ds-BCN delivers an apparent quantum yield of 7.6% at 400 nm and a solar-to-chemical conversion efficiency of 0.3% for selective 2e-reduction of O2 to H2O2, over 4-fold higher than that of the traditional calcined BCN analogue and superior to the metal-free C3N4-based photocatalysts reported so far. The weak-field electro-flash method and as-induced catalytic site symmetry-breaking methodologically provide a new method for the fast and low-cost fabrication of efficient nonmetallic catalysts toward solar-to-chemical conversions

High-Performance Perovskite Photoanode Enabled by Ni Passivation and Catalysis

Lead halide perovskites have achieved phenomenal successes in photovoltaics due to their suitable bandgaps, long diffusion lengths, and balanced charge transport. However, the extreme susceptibility of perovskites to water or air has imposed a seemingly insurmountable barrier for leveraging these unique materials into solar-to-fuel applications such as photoelectrochemical conversion. Here we developed a CH₃NH₃PbI₃-based photoanode with an ultrathin Ni surface layer, which functions as both a physical passivation barrier and a hole-transferring catalyst. Remarkably, a much enhanced photocurrent density, an unassisted photoelectrochemical conversion capability, and a substantially better stability against water have been achieved, which are exceeding most of the previously reported photoanodes as well as a similar CH₃NH₃PbI₃-based device structure but without the Ni surface layer. Our study suggests many exciting opportunities of developing perovskite-based solar-to-fuel conversion

Carbon-Coated Co³⁺-Rich Cobalt Selenide Derived from ZIF-67 for Efficient Electrochemical Water Oxidation

Oxygen evolution reaction (OER) electrocatalysts are confronted with challenges such as sluggish kinetics, low conductivity, and instability, restricting the development of water splitting. In this study, we report an efficient Co³⁺-rich cobalt selenide (Co_0.85Se) nanoparticles coated with carbon shell as OER electrocatalyst, which are derived from zeolitic imidazolate framework (ZIF-67) precursor. It is proposed that the organic ligands in the ZIF-67 can effectively enrich and stabilize the Co³⁺ ions in the inorganic–organic frameworks and subsequent carbon-coated nanoparticles. In alkaline media, the catalyst exhibits excellent OER performances, which are attributed to its abundant active sites, high conductivity, and superior kinetics

WO₃ Nanoflakes for Enhanced Photoelectrochemical Conversion

We developed a postgrowth modification method of two-dimensional WO₃ nanoflakes by a simultaneous solution etching and reducing process in a weakly acidic condition. The obtained dual etched and reduced WO₃ nanoflakes have a much rougher surface, in which oxygen vacancies are created during the simultaneous etching/reducing process for optimized photoelectrochemical performance. The obtained photoanodes show an enhanced photocurrent density of ∼1.10 mA/cm² at 1.0 V <i>vs</i> Ag/AgCl (∼1.23 V <i>vs</i> reversible hydrogen electrode), compared to 0.62 mA/cm² of pristine WO₃ nanoflakes. The electrochemical impedance spectroscopy measurement and the density functional theory calculation demonstrate that this improved performance of dual etched and reduced WO₃ nanoflakes is attributed to the increase of charge carrier density as a result of the synergetic effect of etching and reducing