Effects of Anions and pH on the Stability of ZnO Nanorods for Photoelectrochemical Water Splitting
23 Mar 2018-Vol. 3, Iss: 3, pp 3429-3439
TL;DR: This work demonstrates the improved stability of zinc oxide nanorods (ZnO NRs) for the photoanode of solar water splitting under voltage biases by the addition of borate or carbonate ions in the aqueous electrolyte with suitable pH ranges and proposes a possible mechanism for the protective behavior of ZnO in borate and carbonate solutions.
Abstract: This work demonstrates the improved stability of zinc oxide nanorods (ZnO NRs) for the photoanode of solar water splitting under voltage biases by the addition of borate or carbonate ions in the aqueous electrolyte with suitable pH ranges. The ZnO NRs prepared by the hydrothermal method are highly active and stable at pH 10.5 in both borate and carbonate buffer solutions, where a photocurrent higher than 99% of the initial value has been preserved after 1 h polarization at 1.5 V (vs reversible hydrogen electrode) under AM 1.5G. The optimal pH ranges with a minimum morphological change of ZnO NRs for photoelectrochemical (PEC) water splitting in borate and carbonate buffer solutions are 9-13 and 10-12, respectively. The working pH range for PEC water splitting on ZnO NR photoanodes can be extended to 8.5-12.5 by the combination of borate and carbonate anions. The lifetime of ZnO NR photoanodes can be synergistically prolonged for over an order of magnitude when the electrolyte is the binary electrolyte consisting of borate and carbonate in comparison with these two anions used individually. On the basis of the experimental results, a possible mechanism for the protective behavior of ZnO in borate and carbonate solutions is proposed. These findings can be used to improve the lifetime of other high-performance ZnO-based catalysts and to understand the photocorrosive and protective behaviors of ZnO NRs in the borate and carbonate solutions.
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TL;DR: Detailed electrochemical impedance spectroscopy studies confirm enhanced charge-transfer kinetics and improved conductivity under illumination with minimal effect of interfacial phenomena and establishes MOF materials as favorable candidates for sustainable and efficient design of electrodes for water splitting.
Abstract: The structural diversity of Co(II) metal centers is known to influence their physicochemical properties. A novel two-dimensional (2D) Co(II)-MOF {[Co5(HL)4(dpp)2(H2O)2(μ-OH)2]·21H2O} n has been designed and synthesized by adopting a mixed-ligand strategy, using 1,3-di(4-pyridyl)propane (dpp) colinker with a flexible spacer H3L (H3L: 5-(2 carboxybenzyloxy)isophthalic acid). Co(II)-MOF features a 2D network, which is further interpenetrated among the equivalent sets and therefore results in a 3D supramolecular network. Topologically, the entire network can be viewed as a (3,4,8)-connected three-nodal net with the extended point symbol of {4.5.7}4{412.52.710.94}{52.8.92.10}2, duly assigned to the novel topological type smm2. The functional utility of Co(II)-MOF is demonstrated by employing it toward oxygen evolution reaction (OER) in a photoelectrochemical cell, exhibiting appreciable photocurrents of up to 5.89 mA/cm2 when used as an anode in a photoelectrochemical cell, while also displaying encouraging electrocatalytic currents of 9.32 mA/cm2 (at 2.01 V vs RHE) for the OER. Moreover, detailed electrochemical impedance spectroscopy studies confirm enhanced charge-transfer kinetics and improved conductivity under illumination with minimal effect of interfacial phenomena. This work provides a reference for the expanding field of research into applications of MOF materials and establishes MOF materials as favorable candidates for sustainable and efficient design of electrodes for water splitting.
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References
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TL;DR: Water photolysis is investigated by exploiting the fact that water is transparent to visible light and cannot be decomposed directly, but only by radiation with wavelengths shorter than 190 nm.
Abstract: ALTHOUGH the possibility of water photolysis has been investigated by many workers, a useful method has only now been developed. Because water is transparent to visible light it cannot be decomposed directly, but only by radiation with wavelengths shorter than 190 nm (ref. 1).
27,819 citations
TL;DR: The biggest challenge is whether or not the goals need to be met to fully utilize solar energy for the global energy demand can be met in a costeffective way on the terawatt scale.
Abstract: Energy harvested directly from sunlight offers a desirable approach toward fulfilling, with minimal environmental impact, the need for clean energy. Solar energy is a decentralized and inexhaustible natural resource, with the magnitude of the available solar power striking the earth’s surface at any one instant equal to 130 million 500 MW power plants.1 However, several important goals need to be met to fully utilize solar energy for the global energy demand. First, the means for solar energy conversion, storage, and distribution should be environmentally benign, i.e. protecting ecosystems instead of steadily weakening them. The next important goal is to provide a stable, constant energy flux. Due to the daily and seasonal variability in renewable energy sources such as sunlight, energy harvested from the sun needs to be efficiently converted into chemical fuel that can be stored, transported, and used upon demand. The biggest challenge is whether or not these goals can be met in a costeffective way on the terawatt scale.2
8,037 citations
TL;DR: The rational synthesis of nitrogen-doped zinc oxide (ZnO:N) nanowire arrays, and their implementation as photoanodes in photoelectrochemical (PEC) cells for hydrogen generation from water splitting applications suggest substantial potential of metal oxide nanowires arrays with controlled doping in PEC water splitting Applications.
Abstract: We report the rational synthesis of nitrogen-doped zinc oxide (ZnO:N) nanowire arrays, and their implementation as photoanodes in photoelectrochemical (PEC) cells for hydrogen generation from water splitting. Dense and vertically aligned ZnO nanowires were first prepared from a hydrothermal method, followed by annealing in ammonia to incorporate N as a dopant. Nanowires with a controlled N concentration (atomic ratio of N to Zn) up to ∼4% were prepared by varying the annealing time. X-ray photoelectron spectroscopy studies confirm N substitution at O sites in ZnO nanowires up to ∼4%. Incident-photon-to-current-efficiency measurements carried out on PEC cell with ZnO:N nanowire arrays as photoanodes demonstrate a significant increase of photoresponse in the visible region compared to undoped ZnO nanowires prepared at similar conditions. Mott−Schottky measurements on a representative 3.7% ZnO:N sample give a flat-band potential of −0.58 V, a carrier density of ∼4.6 × 1018 cm−3, and a space-charge layer of ∼...
1,047 citations
877 citations
01 Jan 2012
TL;DR: In this article, the basic principles of photoelectrochemical cells and their properties and properties are discussed. And a discussion of emerging trends in Water Photoelectrolysis is presented.
Abstract: Part I: Basic Principles: Introduction.- Principles of Photoelectrochemical Cells.- Photoelectrochemical Measurements.- Part II: Materials Properties and Synthesis: Nanostructured alpha-Fe2O3 Photoanodes.- Mixed Metal Oxide Photoelectrodes and Photocatalysts.- Combinatorial Identification and Optimization of New Oxide Semiconductors.- Part III: Devices and Device Characterization.- Multijunction Approaches to Photo-electrochemical Water Splitting.- Part IV: Future Perspectives.- Economic and Business Perspectives.- Emerging Trends in Water Photoelectrolysis.
512 citations