A three-dimensional hexagonal fluorine-doped tin oxide nanocone array: a superior light harvesting electrode for high performance photoelectrochemical water splitting

<div> Photonic nanostructures hold great promise in promoting light harvesting. Here&nbsp;</div> <div> &nbsp;</div> <div> we report the first design and construction of a three-dimensional (3D) hexagonal&nbsp;</div> <div> &nbsp;</div> <div> nanocone array of fluorine-doped tin oxide (FTO) on glass as an excellent electrode&nbsp;</div> <div> &nbsp;</div> <div> for photoelectrochemical (PEC) water splitting. The PEC current density with&nbsp;</div> <div> &nbsp;</div> <div> suitably deposited Ti-doped hematite at 1.23 V vs. the reversible hydrogen electrode&nbsp;</div> <div> &nbsp;</div> <div> (RHE) was increased by 86% to 2.24 +/- 0.02 mA cm(-2) compared to that with the&nbsp;</div> <div> &nbsp;</div> <div> planar counterpart, mainly ascribable to the special light harvesting effect and the&nbsp;</div> <div> &nbsp;</div> <div> electrode surface area provided by 3D FTO. Upon the embedment of a gold layer to&nbsp;</div> <div> &nbsp;</div> <div> concentrate the incident light onto the hematite layer and the deposition of the&nbsp;</div> <div> &nbsp;</div> <div> Co-Pi catalyst with a modified procedure, the photocurrent experienced a large&nbsp;</div> <div> &nbsp;</div> <div> cathodic shift of onset potential by 360 mV and soared to a high value of 3.39 +/-&nbsp;</div> <div> &nbsp;</div> <div> 0.01 mA cm(-2) (at 1.23 V), yielding a power conversion efficiency of 0.70% at a&nbsp;</div> <div> &nbsp;</div> <div> potential as low as 0.88 V vs. RHE.&nbsp;</div

Efficient Photoelectrochemical Water Splitting with Ultrathin films of Hematite on Three-Dimensional Nanophotonic Structures

<span lang="EN-US" style="font-family: &quot;Calibri&quot;,&quot;sans-serif&quot;; font-size: 10.5pt; mso-bidi-font-size: 11.0pt; mso-ascii-theme-font: minor-latin; mso-fareast-font-family: 宋体; mso-fareast-theme-font: minor-fareast; mso-hansi-theme-font: minor-latin; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-bidi-theme-font: minor-bidi; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;"><font color="#000000">Photoelectrochemical (PEC) solar water splitting represents a clean and sustainable approach for hydrogen (H-2) production and substantial research are being performed to improve the conversion efficiency. Hematite (alpha-Fe2O3) is considered as a promising candidate for PEC water splitting due to its chemical stability, appropriate band structure, and abundance. However, PEC performance based on hematite is hindered by the short hole diffusion length that put a constraint on the active layer thickness and its light absorption capability. In this work, we have designed and fabricated novel PEC device structure with ultrathin hematite film deposited on three-dimensional nanophotonic structure. In this fashion, the nanophotonic structures can largely improve the light absorption in the ultrathin active materials. In addition, they also provide large surface area to accommodate the slow surface water oxidation process. As the result, high current density of 3.05 mA cm(-2) at 1.23 V with respect to the reversible hydrogen electrode (RHE) has been achieved on such nanophotonic structure, which is about three times of that for a planar photoelectrode. More importantly, our systematic analysis with experiments and modeling revealed that the design of high performance PEC devices needs to consider not only total optical absorption, but also the absorption profile in the active material, in addition to electrode surface area and carrier collection.</font></span

Three-dimensional metal/oxide nanocone arrays for high-performance electrochemical pseudocapacitors

Three-dimensional (3D) electrodes are critical for enabling high-performance power sources. We report here on the design and fabrication, by combining imprint and soft-printing technologies, of 3D nanocone arrays as a novel platform for high performance pseudocapacitors. Such purpose-built 3D nanocone arrays have the advantages of simplicity/versatility/reliability of fabrication, generality to a vast range of active materials, high electrode surface area, and ease of electrolyte permeation. As a demonstration of principle, Au and MnO2 were sequentially deposited forming a 3D Au/MnOx nanocone array electrode for a pseudocapacitor device. This device achieved a specific mass (areal) capacitance of 840.3 F g(-1) (88.2 mF cm(-2)) at a current density of 2 A g(-1). Additionally, the asymmetric supercapacitor using the Au/MnOx nanocone array as the positive electrode and a carbon-based material as the negative electrode achieved a capacitance of 108.5 F g(-1) at a current density of 1 A g(-1), corresponding to an energy density of as high as 46.8 W h kg(-1) at a power density of 0.72 kW kg(-1). The cell still preserved 96.5% of the initial capacitance even after 2000 cycles at a current density of 2 A g(-1). The initial result is at least on a par with those of the best asymmetric supercapacitors reported so far, and thus bolsters the development value of the conductive nanocone arrays for high-performance supercapacitors and other energy-storage devices