Nanotextured Spikes of α-Fe2O3/NiFe2O4 Composite for Efficient Photoelectrochemical Oxidation of Water.

We demonstrate for the first time the application of p-NiFe2O4/n-Fe2O3 composite thin films as anode materials for light-assisted electrolysis of water. The p-NiFe2O4/n-Fe2O3 composite thin films were deposited on planar fluorinated tin oxide (FTO)-coated glass as well as on 3D array of nanospike (NSP) substrates. The effect of substrate (planar FTO and 3D-NSP) and percentage change of each component (i.e., NiFe2O4 and Fe2O3) of composite was studied on photoelectrochemical (PEC) water oxidation reaction. This work also includes the performance comparison of p-NiFe2O4/n-Fe2O3 composite (planar and NSP) devices with pure hematite for PEC water oxidation. Overall, the nanostructured p-NiFe2O4/n-Fe2O3 device with equal molar 1:1 ratio of NiFe2O4 and Fe2O3 was found to be highly efficient for PEC water oxidation as compared with pure hematite, 1:2 and 1:3 molar ratios of composite. The photocurrent density of 1:1 composite thin film on planar substrate was equal to 1.07 mA/cm2 at 1.23 VRHE, which was 1.7 times higher current density as compared with pure hematite device (0.63 mA/cm2 at 1.23 VRHE). The performance of p-NiFe2O4/n-Fe2O3 composites in PEC water oxidation was further enhanced by their deposition over 3D-NSP substrate. The highest photocurrent density of 2.1 mA/cm2 at 1.23 VRHE was obtained for the 1:1 molar ratio p-NiFe2O4/n-Fe2O3 composite on NSP (NF1-NSP), which was 3.3 times more photocurrent density than pure hematite. The measured applied bias photon-to-current efficiency (ABPE) value of NF1-NSP (0.206%) was found to be 1.87 times higher than that of NF1-P (0.11%) and 4.7 times higher than that of pure hematite deposited on FTO-coated glass (0.044%). The higher PEC water oxidation activity of p-NiFe2O4/n-Fe2O3 composite thin film as compared with pure hematite is attributed to the Z-path scheme and better separation of electrons and holes. The increased surface area and greater light absorption capabilities of 3D-NSP devices result in further improvement in catalytic activities.

All Inorganic Cesium Lead Iodide Perovskite Nanowires with Stabilized Cubic Phase at Room Temperature and Nanowire Array-Based Photodetectors.

Alluring optical and electronic properties have made organometallic halide perovskites attractive candidates for optoelectronics. Among all perovskite materials, inorganic CsPbX3 (X is halide) in black cubic phase has triggered enormous attention recently owing to its comparable photovoltaic performance and high stability as compared to organic and hybrid perovskites. However, cubic phase stabilization at room temperature for CsPbI3 still survives as a challenge. Herein we report all inorganic three-dimensional vertical CsPbI3 perovskite nanowires (NWs) synthesized inside anodic alumina membrane (AAM) by chemical vapor deposition (CVD) method. It was discovered that the as-grown NWs have stable cubic phase at room temperature. This significant improvement on phase stability can be attributed to the effective encapsulation of NWs by AAM and large specific area of these NWs. To demonstrate device application of these NWs, photodetectors based on these high density CsPbI3 NWs were fabricated demonstrating decent performance. Our discovery suggests a novel and practical approach to stabilize the cubic phase of CsPbI3 material, which will have broad applications for optoelectronics in the visible wavelength range.

Lead-Free Perovskite Nanowire Array Photodetectors with Drastically Improved Stability in Nanoengineering Templates.

Organometal halide perovskite materials have triggered enormous attention for a wide range of high-performance optoelectronic devices. However, their stability and toxicity are major bottleneck challenges for practical applications. Substituting toxic heavy metal, that is, lead (Pb), with other environmentally benign elements, for example, tin (Sn), could be a potential solution to address the toxicity issue. Nevertheless, even worse stability of Sn-based perovskite material than Pb-based perovskite poses a great challenge for further device fabrication. In this work, for the first time, three-dimensional CH3NH3SnI3 perovskite nanowire arrays were fabricated in nanoengineering templates, which can address nanowire integration and stability issues at the same time. Also, nanowire photodetectors have been fabricated and characterized. Intriguingly, it was discovered that as the nanowires are embedded in mechanically and chemically robust templates, the material decay process has been dramatically slowed down by up to 840 times, as compared with a planar thin film. This significant improvement on stability can be attributed to the effective blockage of diffusion of water and oxygen molecules within the templates. These results clearly demonstrate a new and alternative strategy to address the stability issue of perovskite materials, which is the major roadblock for high-performance optoelectronics.

Impact of CeO2 modified cathode and PANI modified anode on tannery wastewater fed microbial fuel cell performance.

Microbial fuel cell (MFC) technology is getting acceptance as an emphatic, sustainable and energy efficient alternative of conventional wastewater treatment strategies. MFCs utilize exoelectrogens as biocatalysts to degrade the complex organic substances present in wastewater with simultaneous power generation. The present study was aimed at investigating the impact of MFC electrode's modification with CeO2 nanoparticles and polyaniline (PANI) on its performance characteristics. The hydrothermal approach was employed for the synthesis of CeO2 nanoparticles followed by their deposition on carbon cloth (CC) as MFC cathode, whereas MFC's anode i.e., CF/NF was modified by in-situe deposition of PANI. The synthesized material was characterized with FTIR, XRD, SEM, EDX and BET analysis. The experiments were performed using dual chambered MFC fed with leather tannery wastewater using modified and unmodified electrodes. The highest outcomes of power density and corresponding current density were observed with PANI@NF composite anode and CeO2@CC as cathode i.e., 279.3 mW/m2 corresponding to the current density of 581.8 mA/m2. The same MFC electrode configuration resulted in highest COD reduction, i.e., 80 % and coulombic efficiency of 19.86 %. On the other hand, MFC equipped with PANI@CF anode and CeO2@CC cathode also displayed comparable results. It was ascertained that modification of NF/CF anode with PANI (conductive polymer) and CC cathode with CeO2 nanoparticles have significantly improved the overall MFC operational performance regarding tannery wastewater treatment and bioelectricity generation.

An efficient controller design of a PV integrated single inductor multiple output DC-DC converter for dynamic voltage and low power applications.

In this article, a Single Inductor Multiple Output (SIMO) DC-DC boost converter for driving independent three outputs of dynamic voltage and low power is proposed. Compared with the traditional SIMO DC-DC converter, the proposed work accomplishes (i) independent control of power at each output, (ii) small switch count, (iii) relatively better scalability with increasing output channel, (iv) fast response time, and (v) relatively better efficiency. The core aim of the current article is to implement an efficient controller design of the SIMO DC converter circuit operating in continuous conduction mode for dynamic voltage applications. The SIMO circuit comprises a photovoltaic (PV) array as a renewable energy harvesting source at the input. A hysteretic controller based on direct control with seamless transition control topology is implemented in this model for SIMO operation. This scheme is popular due to its less cost, simple, easy-to-use design architecture, and fast speed of close loop control. The configuration of the solar array is designed to deliver maximum power on the input of the SIMO DC-DC converter. For tracking the maximum power point, incremental conductance with integral control configuration is applied on the PV array with fast speed and efficiency. The MATLAB/Simulink environment is utilized for model configuration. The simulation results show that the proposed SIMO configuration with the PV array provided 100.5 W and 21.7 W for 1000 W/m2 and 250 W/m2, respectively.

A non-catalytic vapor growth regime for organohalide perovskite nanowires using anodic aluminum oxide templates.

In this work, a novel and facile synthesis process to fabricate single crystalline organometal halide perovskite nanowires has been successfully developed. Nanowires were grown in a high density ordered array from metal nanoclusters inside anodic aluminum oxide templates using a non-catalytic chemical vapor deposition method. Specifically, perovskite NWs were grown as a result of the reaction between methylammonium iodide (MAI) and the Pb/Sn (Pb or Sn) metal in anodic aluminum oxide templates under optimal conditions. The characterization results show that there is a reaction zone at the interface between the perovskite material and metal, at the bottom of the anodic aluminum oxide nanochannels. In order to sustain perovskite NW growth, MAI molecules have to diffuse downward through the perovskite NWs to reach the reaction zone. In fact, the reaction is facilitated by the formation of an intermediate product of the metal iodide compound. This suggests that the Pb/Sn metal is converted to PbI2/SnI2 first and then perovskite NWs are formed as a result of the reaction between MAI and PbI2/SnI2 through a vapor-solid-solid process. The optical characterization results demonstrate that the as-synthesized NWs with an ultra-high nanostructure density can serve as ideal candidates for optoelectronic devices, such as solar cells, light-emitting didoes, photodetectors, etc. And the reported growth approach here is highly versatile combining the merits of excellent controllability, cost-effectiveness and tunability on material composition and physical properties.

A-Site Cation Effect on Growth Thermodynamics and Photoconductive Properties in Ultrapure Lead Iodine Perovskite Monocrystalline Wires.

Among the various building blocks beyond polycrystalline thin films, perovskite wires have attracted extensive attention for potential applications including nanolasers, waveguides, field-effect transistors, and more. In this work, millimeter-scale lead iodine-based perovskite wires employing various A-site substitutions, namely, Cs, methylammonium (MA), and formamidinium (FA), have been synthesized via a new type solution method with nearly 100% yield. All of the three millimeter scale perovskite wires (MPWs) compositions exhibit relatively high quality, and CsPbI3 is proven to be monocrystalline along its entire length. Furthermore, the growth thermodynamics of the APbI3 MPWs with respect to A-site cation effect were studied thoroughly by various characterization techniques. Finally, single MPW photodetectors have been fabricated utilizing the APbI3 MPWs for studying the photoconductive properties, which show different sensitivities under illumination. This systematic synthesis method of solution-processed APbI3 (Cs, MA, and FA) MPWs reveals a wide spectrum of additives with different coordination capability that mediates perovskite materials growth. It proved to serve as a new parameter that further aids in the rational process of the polycrystalline organic/inorganic hybrids materials. These MPWs also have the potential to open up new opportunities for integrated nanoelectronics ranging from the nanometer through millimeter length scales.

3D Arrays of 1024-Pixel Image Sensors based on Lead Halide Perovskite Nanowires.

Large-scale and highly ordered 3D perov-skite nanowire (NW) arrays are achieved in nanoengineering templates by a unique vapor-solid-solid reaction process. The excellent material properties, in conjunction with the high integration density of the NW arrays, make them promising for 3D integrated nanoelectronics/optoelectronics. Image sensors with 1024 pixels are assembled and characterized to demonstrate the technological potency.

Fabrication of CuFe2O4/α-Fe2O3 Composite Thin Films on FTO Coated Glass and 3-D Nanospike Structures for Efficient Photoelectrochemical Water Splitting.

Recently, photoelectrochemical conversion (PEC) of water into fuel is attracting great attention of researchers due to its outstanding benefits. Herein, a systematic study on PEC of water using CuFe2O4/ α-Fe2O3 composite thin films is presented. CuFe2O4/ α-Fe2O3 composite thin films were deposited on two different substrates; (1) planner FTO glass and (2) 3-dimensional nanospike (NSP). The films on both substrates were characterized and tested as anode material for photoelectrochemical water splitting reaction. During PEC studies, it was observed that the ratio between two components of composite is crucial and highest PEC activity results were achieved by 1:1 component ratio (CF-1) of CuFe2O4 and α-Fe2O3. The CF-1 ratio sample deposited on planar FTO substrate provided a photocurrent density of 1.22 mA/cm2 at 1.23 VRHE which is 1.9 times higher than bare α-Fe2O3 sample. A significant PEC activity outperformance was observed when CF-1 ratio composite thin films were deposited on 3D NSP. The highest photocurrent density of 2.26 mA/cm2 at 1.23 VRHE was achieved for 3D NSP sample which is around 3.6 times higher than photocurrent density generated by α-Fe2O3 thin film only. The higher photocurrent densities of 3D nanostructured devices compared to planar one are attributed to the enhanced light trapping and increased surface area for photoelectrochemical water oxidation on the surface. The difference between valence and conduction bands of CuFe2O4 and α-Fe2O3 allows better separation of photogenerated electrons and holes at the CuFe2O4/ α-Fe2O3 interface which makes it more active for photoelectrochemical water splitting.