Electrodeposition of Inorganic Oxide/Nanocarbon Composites: Opportunities and Challenges

Conformal Coverage of ZnO Nanowire Arrays by ZnMnO3 : Room-temperature Photodeposition from Aqueous Solution

Compositionally and structurally complex semiconductor oxide nanostructures gain importance in many energy-related applications. Simple and robust synthesis routes ideally complying with the principles of modern green chemistry are therefore urgently needed. Here we report on the one-step, room-temperature synthesis of a crystalline-amorphous biphasic ternary metal oxide at the ZnO surface using aqueous precursor solutions. More specifically, conformal and porous ZnMnO3 shells are photodeposited from KMnO4 solution onto immobilized ZnO nanowires acting not only as the substrate but also as the Zn precursor. This water-based, low temperature process yields ZnMnO3 /ZnO composite electrodes featuring in 1 M Na2 SO4 aqueous solution capacitance values of 80-160 F g-1 (as referred to the total mass of the porous film i. e. the electroactive ZnMnO3 phase and the ZnO nanowire array). Our results highlight the suitability of photodeposition as a simple and green route towards complex functional materials.

Preparation of a High-Performance Asymmetric Supercapacitor by Recycling Aluminum Paper and Filter Components of Heated Tobacco

In this study, Al paper and cellulose acetate (CA) filters derived from heated tobacco waste were successfully converted into current collectors and active materials for a supercapacitor device. Typically, heated tobacco contains electrically discontinuous Al paper. First, Al was extracted from the tobacco waste using HCl to produce Lewis acid (AlCl3). This acid was then used in an Al electrodeposition process utilizing the chloroaluminate ionic liquid reaction between the acid and the base (RCl) at room temperature. To enhance the conductivity, a supplementary coating of Al metal was applied to the Al paper through electrodeposition, thus re-establishing the electrical continuity of the discontinuous parts and forming an Al-coated current collector. Moreover, the CA filters were carbonized under a nitrogen atmosphere, yielding carbon precursors (C-CA) for the supercapacitor electrodes. To further enhance the electrochemical performance, nickel oxide (NiO) was incorporated into C-CA, resulting in C-CA@NiO with pseudocapacitance. The specific surface area of CA increased with carbonization and the subsequent incorporation of NiO. The as-synthesized C-CA and C-CA@NiO materials were applied to an Al-coated current collector to obtain C-CA- and C-CA@NiO-based electrodes, exhibiting stable electrochemical behavior in the voltage range of -1.0 to 0 V and 0 to 1.0 V, respectively. An asymmetric supercapacitor (ASC) device was assembled with C-CA@NiO and C-CA as the positive and negative electrodes, respectively. This ASC device demonstrated a high specific capacitance of 40.8 F g-1, while widening the operating voltage window to 2.0 V. The high electrochemical performance of the device is attributed to the successful Al electrodeposition, which facilitates the electrical conductivity and increased porosity of the C-CA@NiO and C-CA materials. To the best of our knowledge, this is a pioneering study in regards to the conversion of biomass waste into current collectors and active materials to fabricate a practical ASC device. Our findings highlight the potential of reusing Al paper and CA filters from heated tobacco waste as essential components of energy storage devices.

Hybrid FeNiOOH/α-Fe2O3/Graphene Photoelectrodes with Advanced Water Oxidation Performance

In this study, the photoelectrochemical behavior of electrodeposited FeNiOOH/Fe2O3/graphene nanohybrid electrodes is investigated, which has precisely controlled structure and composition. The photoelectrode assembly is designed in a bioinspired manner where each component has its own function: Fe2O3 is responsible for the absorption of light, the graphene framework for proper charge carrier transport, while the FeNiOOH overlayer for facile water oxidation. The effect of each component on the photoelectrochemical behavior is studied by linear sweep photovoltammetry, incident photon-to-charge carrier conversion efficiency measurements, and long-term photoelectrolysis. 2.6 times higher photocurrents are obtained for the best-performing FeNiOOH/Fe2O3/graphene system compared to its pristine Fe2O3 counterpart. Transient absorption spectroscopy measurements reveal an increased hole-lifetime in the case of the Fe2O3/graphene samples. Long-term photoelectrolysis measurements in combination with Raman spectroscopy, however, prove that the underlying nanocarbon framework is corroded by the photogenerated holes. This issue is tackled by the electrodeposition of a thin FeNiOOH overlayer, which rapidly accepts the photogenerated holes from Fe2O3, thus eliminating the pathway leading to the corrosion of graphene.

Photoelectrochemical Behavior of PEDOT/Nanocarbon Electrodes: Fundamentals and Structure-Property Relationships

In this study, we investigated the photoelectrochemical behavior of poly(3,4-ethylenedioxythiophene) (PEDOT)/carbon nanotube (CNT) and PEDOT/graphene nanocomposite photoelectrodes for the first time. Electrodeposition allowed control of both the composition and the morphology (as demonstrated by both transmission and scanning electron microscopy images) and also ensured an intimate contact between the PEDOT film and the nanocarbon scaffold. The effect of CNT and graphene on the photoelectrochemical behavior of the nanocomposite samples was studied by linear sweep photovoltammetry, incident photon-to-charge-carrier conversion efficiency measurements, and long-term photoelectrolysis coupled with gas-chromatographic product analysis. We demonstrated that the nanocarbon framework facilitated efficient charge carrier transport, resulting in a 4-fold increase in the measured photocurrents for the PEDOT/CNT electrode, compared to the bare PEDOT counterpart. The presented results contribute to the better understanding of the enhanced photoelectrochemical behavior of organic semiconductor/nanocarbon electrode assemblies and might encourage other researchers to study these intriguing hybrid materials further.

Enhanced Photoelectrochemical Performance of Cuprous Oxide/Graphene Nanohybrids

Combination of an oxide semiconductor with a highly conductive nanocarbon framework (such as graphene or carbon nanotubes) is an attractive avenue to assemble efficient photoelectrodes for solar fuel generation. To fully exploit the possible synergies of the hybrid formation, however, precise knowledge of these systems is required to allow rational design and morphological engineering. In this paper, we present the controlled electrochemical deposition of nanocrystalline p-Cu2O on the surface of different graphene substrates. The developed synthetic protocol allowed tuning of the morphological features of the hybrids as deduced from electron microscopy. (Photo)electrochemical measurements (including photovoltammetry, electrochemical impedance spectroscopy, photocurrent transient analysis) demonstrated better performance for the 2D graphene containing photoelectrodes, compared to the bare Cu2O films, the enhanced performance being rooted in suppressed charge carrier recombination. To elucidate the precise role of graphene, comparative studies were performed with carbon nanotube (CNT) films and 3D graphene foams. These studies revealed, after allowing for the effect of increased surface area, that the 3D graphene substrate outperformed the other two nanocarbons. Its interconnected structure facilitated effective charge separation and transport, leading to better harvesting of the generated photoelectrons. These hybrid assemblies are shown to be potentially attractive candidates in photoelectrochemical energy conversion schemes, namely CO2 reduction.