Defective 3D vertical graphene (VG) with a relatively large surface area, high defect density, and increased surface electrons is synthesized via a scalable plasma enhanced chemical vapor deposition ...method, together with a postsynthesis Ar‐plasma treatment (VG‐Ar). Subsequently, Cu@CuxO nanoparticles are deposited onto VG‐Ar (Cu/VG‐Ar) through a galvanostatic pulsed electrodeposition method. These Cu@CuxO nanocatalyst systems exhibit a superior electrochemical CO2 reduction performance when compared to Cu‐based catalysts supported on commercial graphene paper or pristine VG without postsynthesis Ar‐plasma treatment. The Cu/VG‐Ar achieves the highest CO2 reduction Faradaic efficiency of 60.6% (83.5% of which are attributed to liquid products, i.e., formate, ethanol, and n‐propanol) with a 5.6 mA cm−2 partial current density at −1.2 V versus reversible hydrogen electrode (RHE). The improved CO2 reduction performance of Cu/VG‐Ar originates from the well‐dispersed Cu@CuxO nanoparticles deposited on the defective VG‐Ar. The intrinsic carbon defects on VG‐Ar can suppress the hydrogen evolution reaction as well as tune the interaction between VG and Cu@CuxO, thus impeding the excessive oxidation of Cu2O species deposited on VG‐Ar. The defective VG‐Ar and stabilized Cu@CuxO enhances CO2 adsorption and promotes electron transfer to the adsorbed CO2 and intermediates on the catalyst surface, thus improving the overall CO2 reduction performance.
Defective 3D vertical graphene (VG‐Ar) with sp3‐type intrinsic carbon defects is synthesized via a plasma enhanced chemical vapor deposition method followed by a postsynthesis Ar‐plasma treatment. The sp3‐type intrinsic carbon defects improve the electrochemical CO2 reduction performance of Cu/VG‐Ar by stabilizing the Cu2O species, suppressing the hydrogen evolution reaction process, and channeling electrons to the adsorbed CO2 and intermediates.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Photoelectrocatalysis
The cover image, highlighting the work by Fatwa Firdaus Abdi, Yun Hau Ng, and co‐workers in article number 2102023, shows the photoelectrochemical water oxidation on an ...illuminated plate‐like bismuth tungstate photoanode thin film. The tungsten concentration is modulated to tune the photoexcited charge transportation of the thin film. This “self‐doped” of tungsten leads to the higher carrier density and improved conductivity for oxygen evolution from water.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Pulsed electrodeposition has been introduced to deposit ultrathin flakes of Co3O4 nanocrystals on ZnO nanorods. By fixing the seeding process, the scaffolding function of ZnO nanorods was studied by ...varying deposition times (30 s, 60 s, and 90 s) of Co3O4 at a nucleation current of −1.0 mA cm−2. The amount of deposited Co3O4 has a strong influence on the oxygen evolution performance with ZnO scaffolds. To deliver a current density of 10.0 mA cm−2 in neutral solutions (0.5 M K2SO4), the presence of ZnO scaffold electrodes negatively shifted the overpotential by ∼200 mV. In particular, the Co3O4/ZnO hybrid nanostructured electrode (60 s) exhibits the lowest onset potential of 1.5 V (vs. reversible hydrogen electrode, RHE). Electrochemical impedance spectra and double layer capacitance showed that the enhanced oxygen evolution activities originated from the improved charge transfer capability and the increased electrochemically active interface between Co3O4 and ZnO.
ZnO nanorods arrays serve as an effective scaffold for highly dispersed pulsed‐electrodeposited Co3O4. The increased electrochemically active area at the intimate interface between Co3O4 and ZnO accounts for the material‘s excellent performance in the oxygen evolution reaction.
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FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
In the field of solar water splitting, searching for and modifying bulk compositions have been the conventional approaches to enhancing visible-light activity. In this work, manipulation of ...heterointerfaces in ZnS–GaP multilayer films is demonstrated as a successful alternative approach to achieving visible-light-active photoelectrodes. The photocurrent measured under visible light increases with the increasing number of interfaces for ZnS–GaP multilayer films with the same total thickness, indicating it to be a predominantly interface-driven effect. The activity extends to long wavelengths (650 nm), much longer than those expected for pure ZnS and also longer than those previously reported for GaP. Density functional theory calculations of ZnS–GaP multilayers predict the presence of electronic states associated with atoms at the interfaces between ZnS and GaP that are different from those found within the layers away from the interfaces; these states, formed due to unique bonding environments found at the interfaces, lead to a lowering of the band gap and hence the observed visible-light activity. The presence of these electronic states attributed to the interfaces is confirmed by depth-resolved X-ray photoelectron spectroscopy. Thus, we show that interface engineering is a promising route for overcoming common deficiencies of individual bulk materials caused by both wide band gaps and indirect band gaps and hence enhancing visible-light absorption and photoelectrochemical performance.
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IJS, KILJ, NUK, PNG, UL, UM
Herein, we demonstrate a method used to tune the selectivity of LaNiO3 (LNO) perovskite catalysts through the substitution of La with K cations. LNO perovskites were synthesised using a simple ...sol-gel method, which exhibited 100% selectivity towards the methanation of CO2 at all temperatures investigated. La cations were partially replaced by K cations to varying degrees via control of precursor metal concentration during synthesis. It was demonstrated that the reaction selectivity between CO2 methanation and the reverse water gas shift (rWGS) could be tuned depending on the initial amount of K substituted. Tuning the selectivity (i.e., ratio of CH4 and CO products) between these reactions has been shown to be beneficial for downstream hydrocarbon reforming, while valorizing waste CO2. Spectroscopic and temperature-controlled desorption characterizations show that K incorporation on the catalyst surface decrease the stability of C-based intermediates, promoting the desorption of CO formed via the rWGS prior to methanation.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Highlights
A rational design of metal halide perovskites for achieving efficient CO
2
reduction reaction was demonstrated.
The stability of CsPbI
3
perovskite nanocrystal (NCs) in aqueous electrolyte ...was improved by compositing with reduced graphene oxide (rGO).
The CsPbI
3
/rGO catalyst exhibited > 92% Faradaic efficiency toward formate production with high current density which was associated with the synergistic effects between the CsPbI
3
NCs and rGO.
Transformation of greenhouse gas (CO
2
) into valuable chemicals and fuels is a promising route to address the global issues of climate change and the energy crisis. Metal halide perovskite catalysts have shown their potential in promoting CO
2
reduction reaction (CO
2
RR), however, their low phase stability has limited their application perspective. Herein, we present a reduced graphene oxide (rGO) wrapped CsPbI
3
perovskite nanocrystal (NC) CO
2
RR catalyst (CsPbI
3
/rGO), demonstrating enhanced stability in the aqueous electrolyte. The CsPbI
3
/rGO catalyst exhibited > 92% Faradaic efficiency toward formate production at a CO
2
RR current density of ~ 12.7 mA cm
−2
. Comprehensive characterizations revealed the superior performance of the CsPbI
3
/rGO catalyst originated from the synergistic effects between the CsPbI
3
NCs and rGO, i.e., rGO stabilized the α-CsPbI
3
phase and tuned the charge distribution, thus lowered the energy barrier for the protonation process and the formation of *HCOO intermediate, which resulted in high CO
2
RR selectivity toward formate. This work shows a promising strategy to rationally design robust metal halide perovskites for achieving efficient CO
2
RR toward valuable fuels.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
•Cuprous oxide has great potential in photocatalysis but suffering from photocorrosion.•Photocorrosion can be induced by photo-reduction or photo-oxidation, respectively.•Strategies can be formulated ...for photocorrosion suppression but understandings of the charge dynamics are also important.
The emergence of cuprous oxide (Cu2O) as a visible light active semiconductor for photocatalytic and photoelectrochemical applications has elevated significantly over the past decade. With photocorrosion identified as a severe issue for Cu2O, its photoactivity has been greatly restricted. Given that Cu2O redox potentials are located in between its band gap, the possible occurrence of self-photoreduction or self-oxidation upon illumination is inevitable. Various efforts have been directed to implement effective strategies in enhancing the photostability of Cu2O. In particular, most of the studies focused on improving the charge transfer from Cu2O to reactants or co-catalyst to avoid accumulation of charge within the particles. This review presents recent research progresses for the development of strategies to suppress Cu2O photocorrosion in regards to its intrinsic properties and charge kinetics. It is shown that effective transport of electrons or holes out of Cu2O photocatalyst by engineering its crystal structure, tuning its reaction environment or depositing secondary elements could effectively inhibit Cu2O from experiencing self-photodecomposition. Understanding of the charge dynamics with respect to its photocorrosion is pivotal to optimize the design of Cu2O photocatalyst for enhanced performance in the future.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Invited for this month's cover are the collaborative groups of Dr. Yun Hau Ng at University of New South Wales, Australia and Dr. Yiming Tang at South China Normal University, China. The front cover ...picture shows ultrathin Co3O4 nanoflakes that are deposited on ZnO nanorods by pulsed electrodeposition. The performance of the nanostructured hybrid Co3O4/ZnO anode in electrochemical O2 evolution is better than that of neat Co3O4. Well‐aligned one‐dimensional ZnO nanorod arrays are integrated as a scaffold which functions as a “highway” to facilitate improved charge transfer, while the porosity of the anode material allows the penetration of the electrolyte, thus promoting efficient utilization of the catalytically active species. Read the full text of the article at 10.1002/cplu.201800218.
“This unique pulsed‐electrodeposition method is not limited to the fabrication of electrodes for efficient oxygen evolution reaction (OER) as demonstrated in this paper; it has shown its versatility in the preparation of nanostructured thin films for different applications, including electrochemical sensing, photoelectrochemical water splitting and solar cells.” Read more about the story behind the cover in the Cover Profile and about the research itself (DOI: 10.1002/cplu.201800218).
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FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
Cuprous Oxide (Cu2O) is a photocatalyst with severe photocorrosion issues. Theoretically, it can undergo both self‐oxidation (to form copper oxide (CuO)) and self‐reduction (to form metallic copper ...(Cu)) upon illumination with the aid of photoexcited charges. There is, however, limited experimental understanding of the “dominant” photocorrosion pathway. Both photocorrosion modes can be regulated by tailoring the conditions of the photocatalytic reactions. Photooxidation of Cu2O (in the form of a suspension system), accompanied by corroded morphology, is kinetically favourable and is the prevailing deactivation pathway. With knowledge of the dominant deactivation mode of Cu2O, suppression of self‐photooxidation together with enhancement in its overall photocatalytic performance can be achieved after a careful selection of sacrificial hole (h+) scavenger. In this way, stable hydrogen (H2) production can be attained without the need for deposition of secondary components.
Photoangeregtes Cu2O kann auf zwei möglichen Wegen photokorrodieren: selbständige Photoreduktion zu Cu‐Metall oder selbständige Photooxidation zu CuO. Eine systematische Studie der Cu2O‐Photokorrosion zeigt, dass selbständige Photooxidation unter Vernichtung von photogenerierten Löchern (h+) der dominierende Vorgang in diesem Prozess ist. Skalierung: 100 nm.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Photoreforming ethanol to simultaneously produce hydrogen and value-added organic products was realized over defected TiO2. Chemically induced defects in TiO2 promoted light absorption and charge ...separation, enhancing overall photoactivity. The induced defects also regulated product selectivity, leading to greater hydrogen purity and liquid to gaseous carbon ratio. The optimal catalyst generated 0.08 mmol/hr of hydrogen with a purity greater than 99 % and 0.08 mmol/hr of liquid acetaldehyde over a 6 hr timeframe. This was three times greater than the untreated TiO2. Active species trapping revealed that the preferred ethanol oxidation pathway was direct hole transfer, indicating the selectivity relies on surface chemisorption. Surface defects decreased the acetaldehyde adsorption energy, instigating its prompt desorption and suppressing overoxidation into CO2, thus improving the selectivity towards hydrogen and liquid hydrocarbon products. The work offers an alternative approach towards sustainable energy by coupling photocatalysis with waste organic utilization.
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•Defected TiO2 prepared via a facile chemical reduction delivered improved product selectivity over ethanol photoreforming.•Enhanced light absorption and charge carrier separation by the TiO2 defects elevated photoreforming activity.•The defected TiO2 gave higher H2 and acetaldehyde selectivity by suppressing CO2 generation from ethanol over-oxidation.•Surface defects contributed to selectivity enhancement by altering intermediate chemisorption.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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