Activity For Overall Water Splitting Research Articles

(Invited) Dye-Sensitized Oxide Nanosheets for Visible-Light Water Splitting

Metal oxide nanosheets derived from the layered counterparts have attracted attention in various fields due to their unique structural properties. The anisotropic feature of nanosheets, having a thickness of ~1 nm and lateral dimensions ranging from several hundred nanometers to a few micrometer, is advantageous for heterogeneous photocatalysis, as the diffusion length of photogenerated carriers to the surface is shortened, leading to higher activity. It is also known that certain nanoparticulate metals or metal oxides on a semiconductor photocatalyst work as cocatalysts to promote water reduction and/or oxidation. In heterogeneous photocatalysis, the effect of cocatalyst size on the water-splitting performance had not been examined at sizes smaller than 1 nm due to the lack of an effective preparation method and a suitable photocatalyst. We have demonstrated that metal nanoclusters (such as Pt) of <1 nm in size could be deposited on the interlayer nanospace of KCa2Nb3O10 using the electrostatic attraction between a cationic metal complex and a negatively charged Ca2Nb3O10 – sheet, without the aid of any additional reagent. The material obtained exhibited 8 times greater photocatalytic activity for overall water splitting under band-gap irradiation than the previously reported analog using a RuO2 promoter. This study highlighted the superior functionality of <1 nm Pt nanoclusters for photocatalytic overall water splitting. With further modification by a ruthenium(II) photosensitizer, this material also worked as a H2 evolution photocatalyst in visible-light-driven Z-scheme water splitting, in combination with a WO3-based O2 evolution photocatalyst and a triiodide/iodide redox couple. Pt-intercalated HCa2Nb3O10 nanosheets further modified with amorphous AlO x clusters demonstrated a remarkable photocatalytic activity with a dye-based turnover number and frequency for H2 evolution of 4580 and 1960 h–1, respectively, which were by far the highest among dye-sensitized nonsacrificial photocatalytic systems ever reported.

In situ fabrication of cobalt/nickel sulfides nanohybrid based on various sulfur sources as highly efficient bifunctional electrocatalysts for overall water splitting

AbstractTransition metal chalcogenides are attractive electrocatalysts for oxygen evolution reaction (OER) or hydrogen evolution reaction (HER) due to their natural abundance and diverse structure. Herein, nickel sulfides (Ni3S2) and nickel/cobalt sulfides nanohybrid have been in situ fabricated on nickel foam (NF) by a facile hydrothermal method with sodium sulfide (Ss), L‐cysteine (Lc) or thiourea (Tu) as a sulfur source, respectively. The results show that sulfur source has a great influence on the phase structure, morphology and electrocatalytic performance of transition metal sulfides. The nickel sulfide with the sodium sulfide as a sulfur source (NiSs) shows better HER and OER activity in 1 M KOH. With the Co‐doping, three‐dimensional honeycomb‐like NiCoSs nanosheet clusters exhibits the enhanced electrocatalysis properties with overpotentials of only 168 mV at 10 mA cm–2 for HER and 234 mV at 20 mA cm–2 for OER, respectively. The NiCoSs shows the good bifunctional activities for overall water splitting and presents considerable stability for 24 hours. The good electrochemical activities of metal sulfides by using inorganic sodium sulfide can be attributed to the large exposed surface area and heterostructure compositions of Co9S8 and Ni3S2.

Novel S-scheme WO3/RP composite with outstanding overall water splitting activity for H2 and O2 evolution under visible light

Elemental red phosphorus (RP) has an ultra-low activity of splitting water for H2 and O2 evolution. In this study, RP was decorated by trace amount of WO3 to greatly enhance the photocarriers separation and photocatalytic activity for overall water splitting under visible light. The 2.5% WO3/RP composite achieved the highest activity to produce H2 and O2, and the activity was 7.0 times that of pure RP under visible light (λ ≥ 420 nm). The significantly increased photocarriers separation of WO3/RP was ensured by transient photocurrent, electrochemical impendence, photoluminescence, and time-resolved photoluminescence characterizations. More importantly, WO3/RP maintained high stability when it was persistently used for 20 cycles. Based on the reactive oxygen species (O2− and OH) detected during the photocatalytic process, an S-scheme mechanism was proposed for WO3/RP composites to efficiently separate the photocarriers. This work provides a notion for improving the overall water splitting activity of RP via an S-scheme photocarriers separation mode.

A Trimetallic Cobalt/Iron/Nickel Phytate Catalyst for Overall Water Splitting: Fabrication by Magnetic-Field-Assisted Bipolar Electrodeposition.

Electrodeposition is an effective method to prepare various materials. We have established a bipolar electrodeposition system assisted by a constant magnetic field to fabricate a Co/Fe/Ni phytate catalyst with good electrocatalytic activity for overall water splitting. The effects of magnetic and electric fields on the catalytic properties of the material were studied. The catalyst prepared with an N-pole magnetic field (NPMF) exhibited good overall water splitting performance. Benefiting from the synergistic effect of the Co/Fe/Ni-phytate and the advantages of the N-pole magnetic field the NPMF electrode has a continuous 25 hours high-efficiency hydrogen evolution and oxygen evolution reaction at a current density of 100 mA cm-2 in1.0 M KOH compared with commercial RuO2 and Pt/C. Bipolar electrodeposition with a constant magnetic field is thus an efficient means to fabricate electrocatalytic water splitting catalysts.

Cobalt phosphide nanowires with adjustable iridium, realizing excellent bifunctional activity for acidic water splitting.

The exploration of highly active bifunctional electrocatalysts for acidic electrochemical water splitting has attracted wide attention due to their importance in polymer electrolyte membrane (PEM) electrolyzers. However, existing catalysts normally suffer from low catalytic efficiency under acidic conditions. Herein, we developed a series of Ir-doped CoP nanowires arrays on carbon cloth (Ir-CoP/CC) materials, realizing prominently improved bifunctional catalytic activity for overall water splitting in an acidic medium. The optimized Ir4-CoP/CC catalyst exhibits the smallest overpotential of 38 mV and 237 mV to reach 10 mA cm-2 for HER and OER, respectively. Through systematic experimental research, we find the best intrinsic activity belongs to Ir3-CoP/CC catalyst, which presents superior bifunctional performance with the most economical usage of Ir. As a result, the best acidic water splitting electrolyzer displays a very low voltage of 1.50 V at 10 mA cm-2. This work provides a novel strategy to develop highly active bifunctional catalysts for acidic electrochemical water splitting.

Hollow ZIF-67 derived porous cobalt sulfide as an efficient bifunctional electrocatalyst for overall water splitting

A hollow ZIF-67 templating approach was used to fabricate a hollow cobalt sulfide superstructure with enhanced activity for overall water splitting.

Integrating NiMoO wafer as a heterogeneous ‘turbo’ for engineering robust Ru-based electrocatalyst for overall water splitting

• Hybrid nanostructure of RuO 2 and NiMoO was fabricated via highly matched lattices. • Integrated NiMoO works like a turbo through optimizing the intermediates adsorption. • RuO 2 -NiMoO exhibits enhanced electrocatalytic activity for overall water splitting. • The synergy among geometric, electronic, and interfacial structures is crucial. Cooperative promotions of intrinsic activity, active sites amount, and mass transfer/charge transport in electrocatalytic process are highly depending on the fundamental understanding of reaction mechanism and the systematic and elaborate designing of morphological, electronic, and interfacial structure of electrocatalyst. Herein, a hybrid nanostructure of RuO 2 strongly coupled with structurally controllable NiMoO wafer arrays was elaborately fabricated via highly matched lattices for superior alkaline water electrolysis through optimizing the adsorption energies of the key intermediates at the interface based on synergistic electronic, geometric, and interfacial effects. The incorporation of Mo ion can adjust the electronic structure of host NiO x endowing the resultant NiMoO with suitable H and O intermediate binding energy for active species transfer between the interfaces. The ratio of O/C on the surface of flexible carbon cloth was well tuned through O 2 -plasma to achieve the desired geometric structure of NiMoO wafers with features of rich porosity and abundant active site. The RuO 2 nanoparticles are homogeneously distributed on the surface of porous NiMoO wafers via highly matched lattices, thereby offering efficient interfacial synergy. Consequently, the hybrid nanostructure of Ru species and NiMoO exhibits greatly enhanced bifunctional electrocatalytic activities toward both HER and OER for overall water splitting. The integrated NiMoO wafer works like a turbo for engineering robust Ru-based bifunctional electrocatalyst. The finding may provide insights for the rational design of advanced nanocomposite catalysts for various energy conversion applications.

Interface Engineering of Partially Phosphidated Co@Co-P@NPCNTs for Highly Enhanced Electrochemical Overall Water Splitting.

Interface engineering is promising but still challenging for developing highly efficient and stable non-noble-metal-based electrocatalysts for water splitting. Herein, partially phosphidated core@shell Co@Co-P nanoparticles encapsulated in bamboo-like N, P co-doped carbon nanotubes (denoted as Part-Ph Co@Co-P@NPCNTs) are prepared through a pyrolysis-oxidation-phosphidation strategy. In this structure, each Co nanoparticle is covered with a thin Co-P layer to form a special core@shell heterojunction interface, and the core@shell structure is further encapsulated by N, P co-doped CNTs that not only protect the Co from corrosion but also guarantee an effective and fast electron transfer on cobalt phosphide. As a bifunctional catalyst for both the hydrogen evolution reaction and oxygen evolution reaction, it exhibits an excellent activity for overall water splitting, and enables long-term operation without significant degradation. Density functional theory calculations demonstrate that the interface of the Co/Co2 P heterojunction could lower the values of ΔGH * (hydrogen adsorption) and ΔGB (water dissociation), which are negatively correlated to the j10 , because of the electronic structures of up-shifted d-band center. This study not only presents an efficient and stable electrocatalyst for overall water splitting but also provides a special route for the interface engineering of heterostructures.

Enhancing visible-light photocatalytic activity for overall water splitting in UiO-66 by controlling metal node composition

The photocatalytic activity of a series of five UiO-66 (M: Zr, Zr/Ti, Zr/Ce, Zr/Ce/Ti, Ce) materials for overall water splitting with generation of hydrogen and oxygen has been herein measured. The most efficient photocatalyst for the overall water splitting is the trimetallic MOF UiO-66(Zr/Ce/Ti) which achieves 230 μ mol ∙ g−1 of H2 and 110 μ mol ∙ g−1 of O2, upon UV light irradiation, and 210 μ mol ∙ g−1 of H2 and 70 μ mol ∙ g−1 of O2, under visible light irradiation. These productivity data indicate that a considerable percentage of its photocatalytic activity derives from the visible region of the spectrum (λ > 450 nm). The photocatalytic activity of trimetallic UiO-66(Zr/Ce/Ti) was maintained upon reuse. Kinetics of the charge separated state monitored by transient absorption spectroscopy shows similar deactivation profiles for the five UiO-66 samples, suggesting that it is the charge separation efficiency the main factor responsible for the differences in the photocatalytic activity. The use of methanol as sacrificial agent during the photocatalytic experiments indicated that the high photocatalytic efficiency for overall water splitting in UiO-66(Zr/Ce/Ti) derives from the favorable kinetics of oxygen evolution. These results show the potential of multimetallic metal-organic frameworks as solar photocatalysts by tuning light absorption towards the visible region.

Molecular-level insights on the reactive facet of carbon nitride single crystals photocatalysing overall water splitting

Unraveling how reactive facets promote photocatalysis at the molecular level remains a grand challenge, while identification of the reactive facets can provide guidelines for designing highly efficient photocatalysts and unravelling the microscopic mechanisms behind them. Recently, a series of polytriazine imides (PTIs) was reported with highly crystalline structures; all had a relatively low photocatalytic activity for overall water splitting. Here, high-angle annular dark-field scanning transmission electron microscopy, energy dispersive spectroscopy mapping, and aberration-corrected integrated differential phase contrast imaging were used to study PTI/Li+Cl− single crystals before and after in situ photodeposition of co-catalysts, showing that the prismatic {10 $$\bar 1$$ 0} planes are more photocatalytically reactive than the basal {0001} planes. Theoretical calculations confirmed that the electrons are energetically favourable to transfer toward the {10 $$\bar 1$$ 0} planes. Upon this discovery, PTI/Li+Cl− crystals with different aspect ratios were prepared, and the overall water splitting performance followed a linear correlation with the relative surface areas of the {10 $$\bar 1$$ 0} and {0001} planes. Our controlling of the reactive facets directly instructs the development of highly efficient polymer photocatalysts for overall water splitting. Unlike with inorganic photocatalysts, the facet-dependent reactivity of conjugated polymers remains elusive. Now, the authors provide molecular-level insights on the reactive facets of crystalline poly(triazine imide) intercalated with LiCl and achieve a remarkable improvement in its overall photocatalytic water splitting activity.

Vapor-Phase Photocatalytic Overall Water Splitting Using Hybrid Methylammonium Copper and Lead Perovskites.

Films or powders of hybrid methylammonium copper halide perovskite exhibit photocatalytic activity for overall water splitting in the vapor phase in the absence of any sacrificial agent, resulting in the generation of H2 and O2, reaching a maximum production rate of 6 μmol H2 × g cat−1h−1 efficiency. The photocatalytic activity depends on the composition, degreasing all inorganic Cs2CuCl2Br2 perovskite and other Cl/Br proportions in the methylammonium hybrids. XRD indicates that MA2CuCl2Br2 is stable under irradiation conditions in agreement with the linear H2 production with the irradiation time. Similar to copper analogue, hybrid methylammonium lead halide perovskites also promote the overall photocatalytic water splitting, but with four times less efficiency than the Cu analogues. The present results show that, although moisture is strongly detrimental to the photovoltaic applications of hybrid perovskites, it is still possible to use these materials as photocatalysts for processes requiring moisture due to the lack of relevance in the photocatalytic processes of interparticle charge migration.

Noble-metal-free Z-Scheme MoS2–CdS/WO3–MnO2 nanocomposites for photocatalytic overall water splitting under visible light

To fabricate an efficient two-component Z-scheme system for visible light induced overall water splitting, CdS/WO3 nanocomposites, with cubic CdS nanoparticles grown on the surface of hexagonal WO3 nanorods, were prepared via a facile precipitation of Cd2+ with S2− in the presence of pre-obtained hexagonal WO3 nanorods. MnO2 and MoS2, the co-catalysts for O2 and H2 generation respectively, were selectively deposited on WO3 and CdS in the CdS/WO3 nanocomposites. The resultant MoS2–CdS/WO3–MnO2 composites show photocatalytic activity for overall water splitting under visible light, with an optimized performance observed over 2.0%MoS2-0.2 CdS/WO3-1.0%MnO2. The visible light induced overall water splitting over MoS2–CdS/WO3–MnO2 nanocomposites can be attributed to the presence of a Z-scheme charge transfer pathway in the CdS/WO3 nanocomposites, ie, the transfer of the photo-generated electrons from the CB of WO3 to the VB of CdS to recombine with the photo-generated holes through an efficient interface between cubic CdS and hexagonal WO3. The left photo-generated holes in VB of WO3 and the photo-generated electrons in CB of CdS therefore can accomplish the water oxidation and water reduction simultaneously, with the assistance of the surface deposited cocatalysts (MnO2 and MoS2). This work demonstrated the great potential of fabricating the two-component direct Z-scheme photocatalytic systems for overall water splitting from two semiconductors with a staggered band structure.

Embedding Co2P nanoparticles into co-doped carbon hollow polyhedron as a bifunctional electrocatalyst for efficient overall water splitting

The reasonable design and construction of non-precious metal electrocatalysts with low cost and high performance is critical for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, a facile polymerization-pyrolysis method is proposed to encapsulate Co2P nanoparticles in co-doped hollow carbon shell by using ZIF-67 and P-containing polymers as precursor. The unique construction not only effectively prevents nanoparticles from detaching, showing good stability after long-term testing, but also provides abundant active sites, large surface areas and large pore volumes, enabling the electrolyte and electrode material to full contact. As expected, the Co2P/NPSC-800 performs superior HER performance with low overpotential of 173 mV at 10 mA cm−2 and excellent stability of 88% retention for 35 h and OER performance with low overpotential of 320 mV at 10 mA cm−2, which endows Co2P/NPSC-800 with good catalytic activity in overall water splitting. Furthermore, density functional theory (DFT) calculations reveal that the metallic property and the decreased reaction barriers of Co2P can promote the catalytic reactions. This work offers an effective route in synthesizing other transition metal phosphides with high catalytic properties.

Cobalt phosphide nanoparticles supported within network of N-doped carbon nanotubes as a multifunctional and scalable electrocatalyst for water splitting

In order to realize industrial production of hydrogen through water splitting, it is essential to develop a cost-efficient and scalable approach to synthesize nonprecious electrocatalysts with sufficiently high activity and stability to replace commercial noble-metal-based electrocatalysts. Herein we synthesize cobalt phosphide nanoparticles dispersed within nitrogen-doped carbon nanotube network ([email protected]) via scalable spray drying and thermal treatments. As a multifunctional electrocatalyst, the [email protected] hybrid delivers outstanding activity for HER (in both acidic and alkaline electrolytes), OER and overall water splitting. Remarkably, it shows an ultra-low overpotental of 94 mV to obtain 10 mA cm−2 in HER. It also demonstrates outstanding activity in overall water splitting, requiring only 1.619 V to deliver 10 mA cm−2 with more than 72 h’ long-term stability. The combination of notable performance, multi-functionality and highly scalable spray-drying synthesis method enables this material as a novel and cost-efficient transition metal-based electrocatalysts for overall water splitting.

Electrodeposited NiSe on a forest of carbon nanotubes as a free-standing electrode for hybrid supercapacitors and overall water splitting

NiSe nanoparticles are electrodeposited over a forest of carbon nanotubes (CNTs) to form an intertwined and porous network. The assynthesized composite (denoted as CNT@NiSe/SS) is used as a free-standing and multifunctional electrode for bothsupercapacitorsand overallwater splitting applications. For a supercapacitor application, CNT@NiSe/SS exhibits higher specific capacity and improved rate capability compared with individual NiSe and CNTs. A hybrid supercapacitor device consisting of battery-like CNT@NiSe/SS and EDLC-like graphene delivers a maximum energy density of 32.1 Wh kg−1 at a power density of 823 W kg−1 and has excellent stability after a floating test of 50 h. On the other hand, CNT@NiSe/SS also serves as a bifunctional electrocatalyst with high activity for overall water splitting. The CNT@NiSe/SS electrode displays excellent hydrogen and oxygen evolution reaction performance with the lowest overpotential of 174 mV at 10 mA cm−2 and 267 mV at 50 mA cm−2, respectively. The symmetrical two-electrode system requires an operating potential of 1.71 V to achieve a current density of 10 mA cm−2. Furthermore, this electrolyzer shows a negligible increment in potential after 24 hof continuouswater splitting. The outstanding performances of CNT@NiSe/SS can be attributed to the synergistic effect of NiSe and CNTs.

Earth-Abundant Transition-Metal-Based Bifunctional Electrocatalysts for Overall Water Splitting in Alkaline Media.

The depletion of fossil fuels has accelerated the search for clean, sustainable, scalable, and environmentally friendly alternative energy sources. Hydrogen is a potential energy carrier because of its advantageous properties, and the electrolysis of water is considered as an efficient method for its industrial production. However, the high-energy conversion efficiency of electrochemical water splitting requires cost-effective and highly active electrocatalysts. Therefore, researchers have aimed to develop high-performance electrode materials based on non-precious and abundant transition metals for conversion devices. Moreover, to further reduce the cost and complexity in real-world applications, bifunctional catalysts that can be simultaneously active on both the anodic (i.e., oxygen evolution reaction, OER) and cathodic (i.e., hydrogen evolution reaction, HER) sides are economically and technically desirable. This Minireview focuses on the recent progress in transition-metal-based materials as bifunctional electrocatalysts, including several promising strategies to promote electrocatalytic activities for overall water splitting in alkaline media, such as chemical doping, defect (vacancy) engineering, phase engineering, facet engineering, and structure engineering. Finally, the potential for further developments in rational electrode materials design is also discussed.

Large‐Size, Porous, Ultrathin NiCoP Nanosheets for Efficient Electro/Photocatalytic Water Splitting

AbstractPorous ultrathin 2D catalysts are attracting great attention in the field of electro/photocatalytic hydrogen evolution reaction (HER) and overall water splitting. Herein, a universal pH‐controlled wet‐chemical strategy is reported followed by thermal and phosphorization treatment to prepare large‐size, porous and ultrathin bimetallic phosphide (NiCoP) nanosheets, in which graphene oxide is adopted as a template to determine the size of products. The thickness of the resultant NiCoP nanosheets ranges from 3.5 to 12.8 nm via delicately adjusting pH from 7.8 to 8.5. The thickness‐dependent electrocatalytic performance is evidenced experimentally and explained by computational studies. The prepared large‐size ultrathin NiCoP nanosheets show excellent bifunctional electrocatalytic activity for overall water splitting, with low overpotentials of 34.3 mV for HER and 245.0 mV for oxygen evolution reaction, respectively, at 10 mA cm−2. Furthermore, the NiCoP nanosheets exhibit superior photocatalytic HER performance, achieving a high HER rate of 238.2 mmol h−1 g−1 in combination with commonly used photocatalyst CdS, which is far superior to that of Pt/CdS (81.7 mmol h−1 g−1). All these results demonstrate large‐size porous ultrathin NiCoP nanosheets as an efficient and multifunctional electro/photocatalyst for water splitting.

The activity enhancement of photocatalytic water splitting by F- pre-occupation on Pt(100) and Pt(111) co-catalyst facets

The reversible hydrogen and oxygen recombination reaction in semiconductor dispersion highly impede the yield increase of photocatalytic water splitting to hydrogen and oxygen. In order to inhibit such reverse reaction, it is necessary to reduce the degree of hydrogen and oxygen adsorption and activiation over co-catalyst on semiconductor. It is known that partial occupation of Pt sites by halogen ions with high electronegativity can decrease the adsorption and activation degree of hydrogen and oxygen molecules over Pt/TiO2, by this way, hydrogen and oxygen recombination reaction can be significantly inhibited, and the overall water splitting activity can be remarkably enhanced. Nevertheless, the detail inhibition mechanism on the reverse recombination reaction by halogen ions occupation on different Pt sites is still unclear. In the present work, by comparing the fluorine ions occupation on different Pt facets, we found that the fluorine ions occupation could decrease the numbers of adsorption sites on Pt(100) and Pt(111) surface. On Pt(100) facet, a fluorine ion occupation affect the four adjacent adsorption sites for H2 and O2 molecules adsorption, while, on Pt(111) surface, a fluorine ion occupation could affect the six adjacent adsorption sites for H2 and O2 molecules adsorption. The difference of fluorine ions occupation on the Pt(100) and Pt(111) facets led to the different adsorption strength of hydrogen and oxygen molecules, which further induced the activiation difference of hydrogen and oxygen on Pt co-catalyst. The results of density functional theory (DFT) calculation indicated that the hydrogen and oxygen adsorption energies on F/Pt(100) were higher than that on F/Pt(111) surface. The H2/O2-TPD, cyclic voltammetry and in-situ XPS experimental results also verified that the hydrogen and oxygen adsorption on F/Pt(100) surface was stronger than that of F/Pt(111) surface. The hydrogen and oxygen recombination experimental results showed that the hydrogen and oxygen recombination rates over F/Pt(100) surface was higher than that of F/Pt(111) surface. Upon light irradiation, the F/Pt(100)/TiO2 photocatalyst exhibited lower activity for overall water splitting than F/Pt(111)/TiO2 photocatalyst. Results in this paper provide a new avenue to promote seimiconductor catalyst for over-all water splitting by tuning the adsorption sites of hydrogen and oxygen on co-catalyst surface.

Multifunctionality of lanthanum-strontium manganite nanopowder.

Manganites are multifunctional materials which are widely used in both technology and devices. In this article, new prospects of their use as nanoparticles for various types of applications are demonstrated. For that, the ferromagnetic nanopowder of La0.6Sr0.4MnO3 has been synthesized by the sol-gel method with a subsequent annealing at 700-900 °C. The crystal structure, phase composition and morphology of nanoparticles as well as magnetic, magnetothermal and electrocatalytic properties have been studied comprehensively. The critical sizes of superparamagnetic, single-domain, and multi-domain states have been determined. It has been established that an anomalously wide temperature range of magnetocaloric properties is associated with an additional contribution to the magnetocaloric effect from superparamagnetic nanoparticles. The maximum values of the specific loss power are observed in the relaxation hysteresis region near the magnetic phase transition temperature. The electrochemical stability and features of the decomposition of nanoparticles in 1 M KOH and Na2SO4 electrolytes have been determined. A decrease in the particle size contributes to an increase in electrocatalytic activity for overall water splitting. Magnetocaloric and electrocatalytic results of the work indicate the prospects for obtaining the possibility of changing the temperature regime of electrocatalysis using contactless heating or cooling.

Nanocrystalline Ga–Zn Oxynitride Materials: Minimized Defect Density for Improved Photocatalytic Activity?

Abstract We present an alternative synthesis strategy for developing nanocrystalline (Ga1−xZnx)(N1−xOx) semiconductors known to be very efficient photoabsorbers. In a first step we produce mixtures of highly crystalline β-Ga2O3 and wurtzite-type ZnO nanoparticles by chemical vapor synthesis. (Ga1−xZnx)(N1−xOx) nanoparticles of wurtzite structure are then formed by reaction of these precursor materials with ammonia. Microstructure as well as composition (zinc loss) changes with nitridation time: band gap energy, crystallite size and crystallinity increase, while defect density decreases with increasing nitridation time. Crystallite growth results in a corresponding decrease in specific surface area. In the UV regime photocatalytic activity for overall water splitting can be monitored for samples both before and after nitridation. We find a significantly lower photocatalytic activity in the nitrided samples, even though the crystallinity is significantly higher and the defect density is significantly lower after nitridation. Both properties should have led to a lower probability for charge carrier recombination, and, consequently, to a higher photocatalytic activity.