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Different environmental and industrial technologies seek for fast and automatic ammonia detection systems, capable of the selective measurement of the concentration of its isotopes at sub-ppm levels, without any interference with the common contaminants. In this work, we report the quasi-simultaneous measurement ofsup14/supNHsub3/subandsup15/supNHsub3/subconcentrations based on a near-infrared diode laser-based photoacoustic system. Using a widely tunable external cavity diode laser, four nearby wavelengths within the range of 1531.3-1531.8 nm were optimal circumstances for sensitive detection, while avoiding interference with water vapor. Subsequently, a more robust distributed feedback diode laser was employed to tune the laser wavelength on the sub-second timescale by varying its driving current rather than using much slower temperature tuning. The detection limit of our system is 0.15 and 0.73 ppm forsup14/supNHsub3/subandsup15/supNHsub3/sub(with an accuracy below 0.1%), respectively, and the response time is 3.5 s.

Electrocatalytic CO2 reduction reaction (CO2RR) in membrane electrode assembly (MEA) systems is a promising technology. Gaseous CO2 can be directly transported to the cathode catalyst layer, leading to enhanced reaction rate. Meanwhile, there is no liquid electrolyte between the cathode and the anode, which can help to improve the energy efficiency of the whole system. The remarkable progress achieved recently points out the way to realize industrially relevant performance. In this review, we focus on the principles in MEA for CO2RR, focusing on gas diffusion electrodes and ion exchange membranes. Furthermore, anode processes beyond the oxidation of water are considered. Besides, the voltage distribution is scrutinized to identify the specific losses related to the individual components. We also summarize the progress on the generation of different reduced products together with the corresponding catalysts. Finally, the challenges and opportunities are highlighted for future research.

Tailoring the hydrophobicity of the cathode gas diffusion electrode mitigates flooding in parallel with enhancing the selectivity of the electrochemical carbon monoxide reduction reaction.

A major goal within the CO2 electrolysis community is to replace the generally used Ir anode catalyst with a more abundant material, which is stable and active for water oxidation under process conditions. Ni is widely applied in alkaline water electrolysis, and it has been considered as a potential anode catalyst in CO2 electrolysis. Here we compare the operation of electrolyzer cells with Ir and Ni anodes and demonstrate that, while Ir is stable under process conditions, the degradation of Ni leads to a rapid cell failure. This is caused by two parallel mechanisms: (i) a pH decrease of the anolyte to a near neutral value and (ii) the local chemical environment developing at the anode (i.e., high carbonate concentration). The latter is detrimental for zero-gap electrolyzer cells only, but the first mechanism is universal, occurring in any kind of CO2 electrolyzer after prolonged operation with recirculated anolyte.

Here, we describe a strategy for preparing CdS/MoS2 heterostructures using initially electrodeposited MoSx on a polycrystalline gold substrate. The excess sulfur intrinsic to the electrodeposited MoS3 surface was derivatized with Cd to form spherical CdS/MoS2 particles by judicious adjustment of the medium pH and interfacial electrochemistry. The progression of this conversion was monitored by a combination of cyclic/linear sweep voltammetry coupled with electrochemical quartz crystal nanogravimetry. The electrodeposited MoSx and CdS/MoS2 films were further characterized by scanning electron microscopy, energy-dispersive X-ray analysis, laser Raman spectroscopy, and X-ray photoelectron spectroscopy. Heterojunction formation between MoS2 and CdS particles was confirmed by high-resolution transmission electron microscopy as well as via Kelvin probe measurements of the contact potential differences, with and without the presence of CdS on the MoS2 surface. The nonoptimized CdS/MoS2 heterostructures showed improved photoelectrochemical response compared with CdS or MoS2 for oxidation of sulfite species.

Titanium dioxide (TiO2) is often employed as a light absorber, electron-transporting material and catalyst in different energy and environmental applications. Heat treatment in a hydrogen atmosphere generates black TiO2 (b-TiO2), allowing better absorption of visible light, which placed this material in the forefront of research. At the same time, hydrogen treatment also introduces trap states, and the question of whether these states are beneficial or harmful is rather controversial and depends strongly on the application. We employed combined surface science and in situ electrochemical methods to scrutinize the effect of these states on the photoelectrochemical (PEC), electrocatalytic (EC), and charge storage properties of b-TiO2. Lower photocurrents were recorded with the increasing number of defect sites, but the EC and charge storage properties improved. We also found that the PEC properties can be enhanced by trap state passivation through Li+ ion intercalation in a two-step process. This passivation can only be achieved by utilizing small size cations in the electrolyte (Li+) but not with bulky ones (Bu4N+). The presented insights will help to resolve some of the controversies in the literature and also provide rational trap state engineering strategies.

Photo-electrochemical production of solar fuels from carbon dioxide, water, and sunlight is an appealing approach. Nevertheless, it remains challenging to scale despite encouraging demonstrations at low power input. Higher current densities require notable voltage input as ohmic losses and activation overpotentials become more significant, resulting in lower solar-to-CO conversion efficiencies. A concentrated photovoltaic cell is integrated into a custom-made heat managed photo-electrochemical device. The heat is transferred from the photovoltaic module to the zero-gap electrolyzer cell by the stream of anodic reactant and produce synergetic effects on both sides. With solar concentrations up to 450suns (i.e., 450kWm−2) applied for the first time to photo-electrochemical reduction of CO2, a partial current for CO production of 4A is achieved. At optimal conditions, the solar-to-CO conversion efficiency reaches 17% while maintaining a current density of 150mAcm−2in the electrolyzer and a CO selectivity above 90%, representing an overall 19% solar-to-fuel conversion efficiency. This study represents a first demonstration of photo-electrochemical CO2reduction under highly concentrated light, paving the way for resource efficient solar fuel production at high power input.

Here, we demonstrate a two-step electrosynthesis approach for the preparation of silver pyrovanadate, Ag4V2O7 in thin-film form. In the first, cathodic step, polycrystalline Ag was deposited on fluorine doped tin oxide (FTO) substrate from a non-aqueous bath. Aqueous pyrovanadate species were then generated by aging of a CO2-infused sodium orthovanadate (Na3VO4) solution for three weeks. Silver ions were subsequently generated in situ in this medium using anodic stripping of the Ag/ITO films from the first step. Interfacial precipitation of the Ag+ ions with the pyrovanadate species afforded the targeted product in phase pure form. The various stages of the electrosynthesis were monitored in situ via the combined use of voltammetry, electrochemical quartz crystal nanogravimetry (EQCN), and coulometry. The Ag4V2O7 thin films were characterized by a variety of experimental techniques, including X-ray diffraction, laser Raman spectroscopy, diffuse reflectance spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. Surface photovoltage spectroscopy, ambient-pressure photoemission spectroscopy, and Kelvin probe contact potential difference (work function) measurements afforded information on the energy band structure of the p-type Ag4V2O7 semiconductor. Finally, the electrochemical and photoelectrochemical properties of the electrosynthesized Ag4V2O7 thin films were studied in both aqueous and non-aqueous electrolytes.

N-doped carbon (N-C) materials are increasingly popular in different electrochemical and catalytic applications. Due to the structural and stoichiometric diversity of these materials, however, the role of different functional moieties is still controversial. We have synthesized a set of N-C catalysts, with identical morphologies (∼27 nm pore size). By systematically changing the precursors, we have varied the amount and chemical nature of N-functions on the catalyst surface. The CO

Interest in silver-based semiconductors dates to the early years of analog photography. On the other hand, the recent discovery of new silver oxide-based ternary semiconductors has caused a resurge...

Visible light irradiation of a mixed halide perovskite film in contact with a solvent (dichloromethane, DCM) in which the film otherwise is stable leads to selective expulsion of iodide (I) from th...

The field of electrochemical carbon dioxide reduction has developed rapidly during recent years. At the same time, the role of the anodic half-reaction has received considerably less attention. In this Perspective, we scrutinize the reports on the best-performing CO2 electrolyzer cells from the past 5 years, to shed light on the role of the anodic oxygen evolution catalyst. We analyze how different cell architectures provide different local chemical environments at the anode surface, which in turn determines the pool of applicable anode catalysts. We uncover the factors that led to either a strikingly high current density operation or an exceptionally long lifetime. On the basis of our analysis, we provide a set of criteria that have to be fulfilled by an anode catalyst to achieve high performance. Finally, we provide an outlook on using alternative anode reactions (alcohol oxidation is discussed as an example), resulting in high-value products and higher energy efficiency for the overall process.

A major goal within the CO2 electrolysis community is to replace the generally used Ir anode catalyst with a more abundant material, which is stable and active for water oxidation under process conditions. Ni is widely applied in alkaline water electrolysis, and it has been considered as a potential anode catalyst in CO2 electrolysis. Here we compare the operation of electrolyzer cells with Ir and Ni anodes and demonstrate that, while Ir is stable under process conditions, the degradation of Ni leads to a rapid cell failure. This is caused by two parallel mechanisms: (i) a pH decrease of the anolyte to a near neutral value and (ii) the local chemical environment developing at the anode (i.e., high carbonate concentration). The latter is detrimental for zero-gap electrolyzer cells only, but the first mechanism is universal, occurring in any kind of CO2 electrolyzer after prolonged operation with recirculated anolyte.

This study focuses on a solid solution series, Ca(La1–xCex)2S4 (0 ≤ x ≤ 1), where the f electron density is absent in CaLa2S4 and is progressively increased until it is maximized in CaCe2S4. Corres...

Solution combustion synthesis (SCS) is shown to be versatile for the rapid-one-pot synthesis of three compounds and four polymorphs in the Cu–V–O ternary family: α-CuV2O6, α- and β-Cu2V2O7, and γ-Cu3V2O8. These compounds feature copper/vanadium stoichiometric ratios ranging from 1:1 to 3:1; their structural, electronic, optoelectronic, and photoelectrochemical attributes were comprehensively characterized by a combination of theoretical and experimental techniques. The main contribution of the present study is the demonstration that a range of stoichiometries in this compound family can be derived simply by tuning the precursor mole ratio in the SCS procedure. The Cu–V–O family of samples, derived by SCS, is shown to exemplify the strong effect of compound stoichiometry on the optoelectronic and photoelectrochemical properties. Overall, α-CuV2O6 showed the best performance, rooted in the direct nature of the optical transition in this material. Finally, SCS is very time-efficient and the various compositi...

Owing to its high hole conductivity and ease of preparation, CuI was among the first inorganic hole-transporting materials that were introduced early on in metal halide perovskite solar cells, but its full potential as a semiconductor material is still to be realized. We have now performed ultrafast spectroelectrochemical experiments on ITO/CuI electrodes to show the effect of applied bias on the excited-state dynamics in CuI. Under operating conditions, the recombination of excitons is dependent on the applied bias, and it can be accelerated by decreasing the potential from +0.6 to −0.1 V vs Ag/AgCl. Prebiasing experiments show the persistent and reversible “memory” effect of electrochemical bias on charge carrier lifetimes. The excitation of CuI in a CuI/CsPbBr3 film provides synergy between both CuI and CsPbBr3 in dictating the charge separation and recombination.

The exfoliation of layered materials into two-dimensional (2D) semiconductors creates new structural domains, for example, basal planes, defect-rich in-planes, and edge sites. These surface species affect the photoelectrochemical (PEC) performance, which in turn determines their applicability in solar energy conversion technologies. In this study, a custom-designed microdroplet cell-based spatially resolved PEC approach was employed to identify the structural parts and to measure the PEC activity of the mechanically exfoliated MoSe2 and WSe2 nanosheets for bulk, few-layer, and monolayer specimens. The PEC performance decreased with the decreasing thickness of nanoflakes, and the relative PEC activity (photo/total current) reduced by introducing more defects to the 2D flakes: 1–3% loss was found for in-plane defects and 30–40% for edge defects. While edge sites act as charge carrier recombination centers, their electrocatalytic activity is higher than that of the basal planes. The comparison of PEC activity of micromechanically and liquid phase exfoliated bulk and few-layer MoSe2 and WSe2 flakes further confirmed that the PEC performance of 2D flakes decreases with an increasing number of edge sites.

Lead halide perovskites (LHPs) have emerged as perspective materials for light harvesting, due to their tunable band gap and optoelectronic properties. Photocatalytic and photoelectrochemical (PEC) studies, employing LHP/liquid junctions, are evolving, where sacrificial reagents are often used. In this study, we found that a frequently applied electron scavenger (TCNQ) has dual roles: while it leads to rapid electron transfer from the electrode to TCNQ, enhancing the PEC performance, it also accelerates the decomposition of the CsPbBr3 photoelectrode. The instability of the films is caused by the TCNQ-mediated halide exchange between the dichloromethane solvent and the LHP film, during PEC operation. Charge transfer and halide exchange pathways were proposed on the basis of in situ spectroelectrochemical and ex situ surface characterization methods, also providing guidance on planning PEC experiments with such systems.

Studying the effect of nanoscale morphology on the photoelectrochemical performance of semiconductor electrodes has been in the forefront of research for over a decade, there are still major inconsistencies and controversies in the literature. Here we aimed to resolve some of these issues, by the controlled preparation of TiO2 photoelectrodes from nanoparticles, nanorods, and nanosheets, where the nano dimension of the 0D, 1D, and 2D structures was kept similar (about 10 nm). XRD, Raman spectroscopy, XPS and UPS were employed to confirm that the chemical nature of the nanostructures is nearly identical, they only differ in their morphology. Photoelectrodes were prepared keeping the loading amount, surface area, or the film thickness identical, to deconvolute all trivial effects, and only scrutinize the role of morphology. TiO2 nanorod (NR) films exhibited the best photoelectrochemical performance in all comparisons, achieving ~4 mA cm−2 at 0.2 V vs. Ag/AgCl (under 100 mW cm−2, Xe-lamp illumination). In stark contrast, TiO2 nanosheet (NS) film showed the lowest performance owing to the small amount of active sites on the basal plane of the NSs and the insufficient charge carrier transport through the film. Overall, we have demonstrated that under carefully controlled conditions, it is possible to compare the PEC behavior of TiO2 photoelectrodes, and that the 1D nanostructures outperformed its 0D and 2D counterparts.

According to the currently accepted structure-property relationships, aceno-pentalenes with angular shape (fused to the 1,2-bond of the acene) exhibit higher antiaromaticity than those with linear shape (fused to the 2,3-bond of the acene). To explore and expand the current view, we designed and synthesized molecules where two isomeric, yet, different, 8π antiaromatic subunits, a benzocyclobutadiene (BCB) and a pentalene are combined into, respectively, an angular and a linear topology via an unsaturated 6-membered ring. The antiaromatic character of the molecules are supported experimentally by 1H NMR, UV-Vis and cyclic voltammetry measurements and X-ray crystallography. The experimental results are further confirmed by theoretical studies including the calculation of several aromaticity indices (NICS, ACID, HOMA, FLU, MCI). In the case of the angular molecule, double bond-localization within the connecting 6-membered ring resulted in reduced antiaromaticity of both the BCB and pentalene subunits, while the linear structure provided a competitive situation for the two unequal [4n]π subunits. We found that in the latter case pentalene drew the shorter straw. The BCB unit alleviated its unfavorable antiaromaticity more efficiently, leaving the pentalene with enhanced antiaromaticity. Thus, a reversed structure-antiaromaticity relationship when compared to aceno-pentalenes was achieved.

This is a perspective of the role that combustion synthesis, specifically solution combustion synthesis, has played in the development of ternary and quaternary metal oxide semiconductors, and materials derived from these compounds such as composites, solid solutions, and doped samples. The attributes of materials, collectively termed ‘complex oxides’ within the context of this discussion, are discussed in terms of their applicability in the generation of solar fuels from water splitting and CO2 reduction, and environmental pollution remediation via heterogeneous photocatalysis.

Electrochemistry, as an analytical tool is gaining its foothold in the characterization of organic metal lead halide per-ovskites, however electrosynthetic applications are yet to be explored fully. Electrochemical deposition of hole-transport layers with desired properties could be an attractive tool to assemble complex solar cell architectures. We have now successfully electropolymerized PEDOT (Poly(3,4-ethylenedioxythiophene)), a hole-transporting material on the surface of methyl-ammonium lead iodide perovskite in a controlled fashion and evaluated its performance in perovskite solar cells. The electrochemical post-treatment protocol is shown to be important to maximize the photo-voltaic performance of the solar cells. The proposed electrochemical deposition methodology expands the pool of tech-niques available for hole transporting layer deposition in perovskite solar cells.

Solar fuel generation is a promising avenue to mitigate the harmful effects of the increasing carbon dioxide concentration in the atmosphere. Both photoelectrochemical water splitting and carbon dioxide reduction are viable pathways to utilize solar irradiation, however, there is a strong need for novel photoelectrode materials with enhanced properties. Copper-based delafossites (CuMO2, where M: Cr, Al, Fe, Rh, etc.) are attractive photocathode candidates because their conduction band position lies at a sufficiently negative potential for both carbon dioxide reduction and hydrogen evolution. In this study copper chromium delafossite (CuCrO2) nanostructures were prepared by solution combustion synthesis; which yielded an almost phase pure, partially crystalline product within five minutes. The nanocrystalline samples were characterized by powder X-ray diffraction, transmission and scanning electron microscopy, UV–vis diffuse reflectance, FT-IR, and Raman spectroscopy. Linear sweep photovoltammograms indicated a promising photoelectrochemical performance (especially after thermal annealing), which is rooted in the interconnected porous structure of the samples. Long-term photoelectrolysis proved that CuCrO2 can reduce carbon dioxide to carbon monoxide, methane, formic acid, and methanol, while hydrogen was co-generated from water splitting. What is further important, CuCrO2 was more resistant to photocorrosion (i.e., metallic copper formation) than its monometallic Cu2O counterpart.

This article focuses on variation in the values for the optical bandgaps ( E g ) experimentally reported for fourteen oxide semiconductors that have been studied for solar photoelectrochemical and photocatalytic environmental remediation applications. Both binary and ternary compounds have been included in this study. The variance in the reported values is much more severe for the ternary compounds relative to the binary counterparts. Factors related to semiconductor doping and size quantization have been carefully removed from playing a role in the presented data. Instead the variability is attributed to intrinsic errors associated with the extraction of E g values from spectral data (for example, via Tauc plots), and to other sample-related factors such as surface functional groups and compound non-stoichiometry. Finally, suggestions for future, follow-up study are also given.