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In this article, we report a simple ex situ Sn-doping method on hematite nanoflakes (coded as MSnO2-H) that can protect the nanoflake (NF) morphology against the 800 degrees C high-temperature annealing process and activate the photoresponse of hematite until 800 nm wavelength excitation. MSnO2-H has been fabricated by dropping SnCl4 ethanol solution on hematite nanoflakes homogeneously grown over the conductive FTO glass substrate and annealed at 500 degrees C to synthesize the SnO2 nanoparticles on hematite NFs. The Sn-treated samples were then placed in a furnace again, and the sintering process was conducted at 800 degrees C for 15 min. During this step, structure deformation of hematite occurs normally due to the grain boundary motion and oriented attachment. However, in the case of MSnO2-H, the outer SnO2 nanoparticles efficiently prevented a shape deformation and maintained the nanoflake shape owing to the encapsulation of hematite NFs. Furthermore, the interface of hematite/SnO2 nanoparticles became the spots for a heavy Sn ion doping. We demonstrated the generation of the newly localized states, resulting in an extension of the photoresponse of hematite until 800 nm wavelength light irradiation. Furthermore, we demonstrated that SnO2 nanoparticles can effectively act as a passivation layer, which can reduce the onset potential of hematite for water splitting redox reactions. The optimized MSnO2-H nanostructures showed a 2.84 times higher photocurrent density and 300 mV reduced onset potential compared with a pristine hematite nanoflake photoanode. Web of Science

Abstract In this work, we examine the photoelectrochemical response of TiO2 layers prepared by reactive DC sputter deposition on conductive glass (FTO). We show that adequate conditioning of the FTO by a very thin (few nm thick) Ti interlayer and optimizing the sputter parameters, compact TiO2 anatase layers can be produced that reach incident photocurrent conversion efficiencies (IPCE) maxima peaking at 75%. This is outperforming many of the best titania photoanode structures (including high surface area 1D and 3D titania structures). The key role of the interlayer is to promote the crystallization of titania in the anatase form during the annealing process (as opposed to rutile in the interlayer-free case). Without this interlayer, an IPCE maxima of ≈43% is obtained for otherwise identically processed electrodes. The present work thus describes a most simple straightforward approach for fabricating compact, high-efficiency TiO2 (anatase) photoanodes. Graphical abstract

Wetting of surfaces plays a vital role in many biological and industrial processes. There are several phenomena closely related to wetting such as biofouling and corrosion that cause the deterioration of materials, while the efforts to prevent the degradation of surface functionality have spread over several millennia. Antifouling coatings have been developed to prevent/delay both corrosion and biofouling, but the problems remain unsolved, influencing the everyday life of the modern society in terms of safety and expenses. In this study, liquid-infused slippery surfaces (LISSs), a recently developed nontoxic repellent technology, that is, a flat variation of omniphobic slippery liquid-infused porous surfaces (SLIPSs), were studied for their anti-corrosion and marine anti-biofouling characteristics on metallic substrates under damaged and plain undamaged conditions. Austenitic stainless steel was chosen as a model due to its wide application in aquatic environments. Our LISS coating effectively prevents biofouling adhesion and decays corrosion of metallic surfaces even if they are severely damaged. The mechanically robust LISS reported in this study significantly extends the SLIPS technology, prompting their application in the marine environment due to the synergy between the facile fabrication process, rapid binding kinetics, nontoxic, ecofriendly, and low-cost applied materials together with excellent repellent characteristics.

Advanced materials 35(5), 2206569 (2023). doi:10.1002/adma.202206569, With recent advances in the field of single-atoms (SAs) used in photocatalysis, an unprecedented performance of atomically dispersed co-catalysts has been achieved. However, the stability and agglomeration of SA co-catalysts on the semiconductor surface may represent a critical issue in potential applications. Here we describe the photoinduced destabilization of Pt SAs on the benchmark photocatalyst, TiO2. In aqueous solutions within illumination timescales ranging from few minutes to several hours, light-induced agglomeration of Pt SAs to ensembles (dimers, multimers) and finally nanoparticles takes place. The kinetics critically depends on the presence of sacrificial hole scavengers and the used light intensity. DFT calculations attribute the light induced destabilization of the SA Pt species to binding of surface-coordinated Pt with solution-hydrogen (adsorbed H atoms), which consequently weakens the Pt SA bonding to the TiO2 surface. Despite the gradual aggregation of Pt SAs into surface clusters and their overall reduction to metallic state, which involves >90% of Pt SAs, the overall photocatalytic H2 evolution remains virtually unaffected., Published by Wiley-VCH, Weinheim

In this work, NiCu co‐catalysts on TiO2 are studied for photocatalytic hydrogen evolution. NiCu co‐catalyst films are deposited at room temperature by argon plasma sputtering on high aspect‐ratio anodic TiO2 nanotubes. To tune the Ni : Cu atomic ratio, alloys of various compositions were used as sputtering targets. Such co‐catalyst films are found to be amorphous with small nanocrystalline domains. A series of parameters is investigated, i. e., i) Ni : Cu relative ratio in the sputtered films, ii) NiCu film thickness, and iii) thickness of the TiO2 nanotube layers. The highest photocatalytic activity is obtained with 8 μm long TiO2 nanotubes, sputter‐coated with a 10 nm‐thick NiCu films with a 1 : 1 Ni : Cu atomic ratio. This photocatalyst reaches a stable hydrogen evolution rate of 186 μL h−1 cm−2, 4.6 and 3 times higher than that of Ni‐ and Cu‐TiO2, respectively, demonstrating a synergistic co‐catalytic effect of Ni and Cu in the alloy co‐catalyst film.

Doping and compositional tuning of Cs(2)AInCl(6) (A = Ag, Na) double perovskite nanocrystals (PNCs) is considered a promising strategy toward the development of light-emitting sources for applications in solution-processed optoelectronic devices. Oleic acid and oleylamine are by far the most often used surface capping ligands for PNCs. However, the undesirable desorption of these ligands due to proton-exchange reaction during isolation and purification processing results in colloidal and structural instabilities. Thus, the improvement of colloidal and optical stability of PNCs represents one of the greatest challenges in the field. Here, we report a trioctylphosphine-mediated synthesis and purification method toward Sb-alloyed Cs2NaInCl6 PNCs with excellent stability and optical features. Nuclear magnetic resonance spectroscopy enabled one to explain the role of trioctylphosphine and to reveal the reaction mechanism during crystal nucleation and growth. Under the optimized reaction conditions, in situ-generated trioctylphosphonium chloride and benzoyl trioctylphosphonium chloride serve as highly reactive halide sources, while benzoyl trioctylphosphonium and oleylammonium cations together with the oleate anion serve as surface capping ligands, which are bound strongly to the PNC surface. The tightly bound ionic pair of oleylammonium oleate and benzoyl trioctylphosphonium chloride/oleate ligands allows one to obtain monodispersed bright-blue-emitting PNCs with high photoluminescence quantum yields exceeding 50% at an optimum Sb content (0.5%), which also exhibit long-term colloidal stability. The approach based on dual cationic ligand passivation of double PNCs opens the doors for applications in other systems with a potential to achieve higher stability along with superior optical properties. Web of Science 13 40 47859 47845

In recent years, the defect engineering of titania via reduction treatments has shown a high potential for enabling efficient and co-catalyst-free photocatalytic H2 generation from methanol/water solutions. However, defect engineering simultaneously alters several properties of TiO2. Here, we use pristine (white) and hydrogenated (gray) anatase nanosheets with dominant (001) facets. By comparing electrical conductivity, photocurrent spectra, transient photocurrent response, and photocatalytic H2 evolution, we show that the increased conductivity or broad visible light absorption of gray titania is not responsible for its increased activity. Instead, the true bottleneck is the hole transfer rate that is significantly accelerated while using gray instead of white modification. Moreover, the hole transfer reaction causes the accumulation of the reaction products in pure water, hindering the photocatalytic H2 evolution over time. These combined factors explain the superior performance of gray titania over white titania in photoelectrochemical or photocatalytic water splitting.

Luminescent solar concentrators (LSCs) are light-harvesting devices that redirect solar light to an edge-attached photovoltaic cell, and thus, they have high potential to be incorporated directly into buildings’ windows to allow for generating electricity. Perovskite nanocrystals (PNCs) are promising materials for LSCs because their enticing optical properties can be engineered to provide a high photoluminescence (PL) quantum yield (QY) and low overlap between absorption and emission spectra. Replacement of toxic, lead-containing perovskites in LSCs by lead-free PNCs, while retaining high optical efficiency of the device, remains the key challenge, which needs to be overcome to build environmentally friendly solar-harvesting platforms. In this work, we use nanocrystals of Bi-doped Cs2Ag0.4Na0.6InCl6 double perovskites with a self-trapped exciton emission to realize for the first time a transparent, low-reabsorption, lead-free perovskite-based LSC. Fabricated 100 cm2 LSCs show an internal optical quantum efficiency of 21.2% with the corresponding internal concentration factor of 2.7. Monte Carlo (MC) ray-tracing simulations identified the loss caused by nonunity PL QY to be the most significant contribution to the overall efficiency loss. The MC simulations also allowed us to estimate the efficiency of 39.4% for 2,500 cm2 LSCs with hypothetical unity PL. These results demonstrate a significant promise held by Bi-doped lead-free PNCs for LSCs.

Reducing the size of a catalyst to a single atom (SA) level can dramatically change its physicochemical properties and significantly boost its catalytic activity. However, the massive synthesis of SA catalysts still remains a grand challenge mainly because of the aggregation and nucleation of the generated atoms during the reaction. Here, we design and implement a spatially confined synthetic strategy based on a porous-hollow carbon nitride (p-CN) coordinated with 1-butyl-3-methylimidazole hexafluorophosphate, which can act as a nanoreactor and allow us to obtain metal SA catalysts (p-CN@M SAs). This relatively easy and highly effective method provides a way to massively synthesize single/multiple atoms (p-CN@M SAs, M = Pt, Pd, Cu, Fe, etc.). Moreover, the amorphous NiB-coated p-CN@Pt SAs can further increase the loading amount of Pt SAs to 3.7 wt %. The synthesized p-CN@Pt&NiB electrocatalyst exhibits an extraordinary hydrogen evolution reaction activity with the overpotential of 40.6 mV@10 mA/cm-2 and the Tofel slope of 29.26 mV/dec.

In the present research, we investigate the synergistic effects of Ru-doping and Ar/H2 reduction treatment on the photoelectrochemical water splitting performance and hydrogen evolution rate of TiO...

Highly ordered and uniform titanium dioxide (TiO2) nanotubes (NTs) with different morphologies (15 nm, 50 nm and 100 nm in diameter) were prepared by the electrochemical anodization of Ti substrates. The TiO2 NTs’ surface properties were characterized by X-ray diffraction (XRD) spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The elastic modulus (E) and the Vickers hardness (HV) of the Ti foil and of the different-morphology TiO2 NTs were evaluated with the nano-indentation technique. E and HV increase with the decreasing length/diameter of the NTs, meaning that NTs with smaller diameters are more resistant to mechanical wear. The elastic modulus of the TiO2 NTs with 15-nm and 50-nm diameters is similar to that of the human bone.

A thin layer of gold nanoparticles (Au NPs) sputtered on cadmium sulfide quantum dots (CdS QDs) decorated anodic titanium dioxide nanotubes (TNTs) (Au/CdS QDs/TNTs) was fabricated and explored for the nonenzymatic detection of cholesterol and hydrogen peroxide (H2O2). Morphological studies of the sensor revealed the formation of uniform nanotubes decorated with a homogeneously dispersed CdS QDs and Au NPs layer. The electrochemical measurements showed an enhanced electrocatalytic performance with a fast electron transfer (∼2 s) between the redox centers of each analyte and electrode surface. The hybrid nanostructure (Au/CdS QDs/TNTs) electrode exhibited about a 6-fold increase in sensitivity for both cholesterol (10,790 μA mM-1 cm-2) and H2O2 (78,833 μA mM-1 cm-2) in analyses compared to the pristine samples. The hybrid electrode utilized different operational potentials for both analytes, which may lead to a voltage-switchable dual-analyte biosensor with a higher selectivity. The biosensor also demonstrated a good reproducibility, thermal stability, and increased shelf life. In addition, the clinical significance of the biosensor was tested for cholesterol and H2O2 in real blood samples, which showed maximum relative standard deviations of 1.8 and 2.3%, respectively. These results indicate that a Au/CdS QDs/TNTs-based hybrid nanostructure is a promising choice for an enzyme-free biosensor due to its suitable band gap alignment and higher electrocatalytic activities.

Constructing an efficient photocatalyst for H2 production generally requires the integration of several functional features in and on a semiconductor platform. This is conventionally done by a classic step-by-step synthesis. Here, we report the self-assembly of an amorphous titania nanotube based system when illuminated for extended time in suitable aqueous solutions. Over time, not only photodeposition of a co-catalyst can take place, but also in situ crystallization and morphology changes occur that can provide a higher H2 production than observed for a classically assembled photocatalyst.

Titanium dioxide (TiO2) is the most frequently studied semiconducting material for photocatalytic water splitting. One of the favored forms of TiO2 for photocatalytic applications is layers of erected single-crystalline anatase nanosheets (NSs), while the most frequently reported substrate used for its synthesis is a fluorine-doped tin oxide (FTO). Herein we demonstrate that anatase TiO2 NS layers can be similarly grown on a Ta2O5 substrate. We found that a Ta2O5 back contact provides a remarkable improvement of the photocatalytic activity of the TiO2 NSs in comparison to a FTO back contact. The TiO2 NSs on Ta2O5 exhibit a 170-fold increase in photocatalytic H2 production rate than that obtained by TiO2 NSs on FTO substrate. The proposed mechanism reveals that such a drastic enhancement of optimized TiO2 NS arrays on the Ta2O5 substrate is attributed to the blocking nature of Ta2O5 for photo-generated electrons in the TiO2 NSs.

Aluminum ion aqueous batteries (AIBs) are among the most promising candidates for high energy density devices due to the multivalent redox processes associated with Al3+ ion intercalation. However, only a few stable AIB electrode materials have been reported so far. MoO3 is a very promising electrode material due to its octahedral layered crystal structure which can accommodate multivalent cation by intercalation. However, the poor electrochemical stability of MoO3 and the sluggish intercalation kinetics of Al3+ ion in Mo oxides electrodes limit its practical application. In this work, we propose a strategy to overcome such shortcomings of MoO3 by fabricating electrodes composed of self-ordered one-dimensional (1D) MoTaOx nanotubes synthesized via electrochemical anodization of Mo-Ta alloy substrates. We show that this approach allows for direct incorporation of Ta in the Mo oxide nanotubes. The resulting MoTaOx nanotubes, composed of octahedral MoO3 and rhombohedral Mo2Ta2O11 phases, exhibit remarkable electrochemical stability and Al-ion storage properties in aqueous electrolytes that are superior to that of pristine Mo oxide or other most efficient electrode materials reported to date. Such MoTaOx nanotube-based electrodes can achieve a specific capacity of 1180 mA h cm-3 (337 mA h g-1, 141 μA h cm-2) at 1.25 A cm-3 (∼0.35 A g-1, 0.15 mA cm-2). More importantly, the capacity retention of such nanotube array electrodes remains above 83% of the initial capacity after 3000 cycles.

Single crystal anatase TiO2 nanosheets (TiO2-NSs) are grown hydrothermally on fluorine-doped tin oxide (FTO). By systematically changing the hydrothermal conditions such as reaction time, initial concentration of Ti precursor, F precursor, and HCl as an additive, a wide variety of TiO2-NSs, with different morphologies and faceting have been synthesized. For the different morphologies and different facet ratios (anatase S001/S001+101), the photoelectrochemical response is characterized and compared. We find that for photoanodes in neutral electrolytes, the magnitude of the photocurrent depends strongly on the growth parameters, that is, peak IPCEs can vary from 11.7% to 61%. For a wide range of parameters, the key parameter deciding on the photocurrent is the effective electrochemically active area of the electrode. Only for very high facet ratios >91%, the photoresponse can be strongly influenced by faceting – for samples with a S001/S001+101 of 91%, IPCE value of ≈84% is obtained. This work defines not only optimized synthesis conditions for a most effective growth of these single crystalline electrode, but also represents fundamental data for further applications of such electrodes.

Herein we systematically investigate the influence of hydrogenation time and temperature on defects formation, structural changes, and co-catalyst free photocatalytic activity for epitaxially grown anatase thin films on strontium titanate single crystals. The photocatalytic activity trend of the anatase epi layers is similar to that of anatase powders and brookite single crystals in reported recent literature, that is, the H2 evolution rate exhibits a typical maximum upon hydrogenation under moderate annealing temperatures (500 °C). By combining surface sensitive X-ray diffraction methods and analytical high-resolution electron microscopy techniques we reveal quantitatively the oxygen loss from the epi-layer ascribed to the hydrogenation (H2 reduction) treatment. We observe specific physicochemical changes associated with the introduction of oxygen vacancies: (i) the formation of a nanoscale strained crystal surface, (ii) the agglomeration of point defects in the bulk of the anatase epi layer, and (iii) a transition towards a Ti2O3 like symmetry at the film surface, i.e. an evident oxygen deficiency at the epi layer surface in particular prominent for the most active sample as a function of the hydrogenation parameters. These extensive experimental findings allow us to propose an empirical model, which links detrimental and beneficial effects of Ti3+ centers and oxygen vacancies in the bulk and at the surface and their abundance to an optimum point defect configuration for water splitting via “grey” anatase.

Herein we introduce for the first time a reduced “grey” brookite TiO2 photocatalyst, produced by thermal hydrogenation of brookite nanoparticles, that shows a remarkable noble metal free photocatalytic H2 evolution. Its activity is substantially higher than that of other TiO2 polymorphs, i.e. anatase or rutile, comparably sized and activated by hydrogenation under optimized conditions. Along with brookite powders, an oriented brookite single crystal was investigated as a defined surface to confirm the effects of the hydrogenation treatment. By a combination of electron paramagnetic resonance (EPR), electron and X-ray characterization techniques applied to the powders and single crystal, we find that hydrogenation forms in brookite a defective crystalline surface layer rich in Ti3+ states. Amorphization effects, i.e. forming the so called “amorphous shell” as reported in previous work for black anatase TiO2, were not detected. Overall, we provide experimental evidence that hydrogenation forms in brookite a surface strained zone with point defects that are mediators for electron transfer to H2O, leading to a significantly enhanced noble metal free photocatalytic H2 evolution in comparison to anatase.

A photocatalysis-enzyme coupled system represents a most promising approach towards artificial photosynthesis and a direct use of solar energy for the synthesis of specific organic molecules or fuel. In contrast to extensively explored semiconductor photocatalysts, studies that successfully combine photocatalytic and enzymatic reactions are rare. In the present work we describe a photocatalyst–enzyme coupled approach that relies on the in situ synthesis of a hierarchically porous (hp) metal–organic framework (here using titania-based MIL-125) formed in the nanochannels of a TiO2 membrane. By engineering the nm-scale pore size in the MOF we achieve trapping of active cytochrome C (CytC). Benefiting from the intrinsic photocatalytic activity of the MOF [MIL-125 (Ti)] we develop a functional photocatalyst–enzyme system that is active under visible light. Moreover, the membrane-based architecture allows for in situ triggering and monitoring of the enzymatic reaction. Therefore, the platform represents not only a nanoscale photocatalytic reactor or device but also allows to monitor and understand photocatalytically coupled enzyme reactions.

ACS applied materials & interfaces 12(34), 38211 - 38221 (2020). doi:10.1021/acsami.0c10968, We investigate the co-catalytic activity of PtCu alloy nanoparticles for photocatalytic H$_{2}$ evolution from methanol-water solutions. To produce the photocatalysts, a few nm-thick Pt-Cu bilayers are deposited on anodic TiO$_{2}$ nanocavity arrays and converted by solid state dewetting, i.e. a suitable thermal treatment, into bimetallic PtCu nanoparticles. XRD and XPS results prove the formation of PtCu nanoalloys that carry a shell of surface oxides. XANES data support Pt and Cu alloying and indicate the presence of lattice disorder in the PtCu nanoparticles. The PtCu co-catalyst on TiO$_{2}$ shows a synergistic activity enhancement and a significantly higher activity towards photocatalytic H$_{2}$ evolution than Pt- or Cu-TiO$_{2}$. We propose the enhanced activity to be due to Pt-Cu electronic interactions, where Cu increases the electron density on Pt favoring a more efficient electron transfer for H$_{2}$ evolution. In addition, Cu can further promote the photo-activity by providing additional surface catalytic sites for hydrogen recombination. Remarkably, when increasing the methanol concentration up to 50 vol% in the reaction phase, we observe for PtCu-TiO$_{2}$ a steeper activity increase compared to Pt-TiO$_{2}$. A further increase in methanol concentration (up to 80 vol%) causes for Pt-TiO$_{2}$ a clear activity decay, while PtCu-TiO$_{2}$ still maintains a high level of activity. This suggests an improved robustness of PtCu nanoalloys against poisoning from methanol oxidation products such as CO., Published by Soc., Washington, DC

Dye-sensitized photocathodes have the potential to significantly contribute to the efficiency of the solar light-to-current conversion in tandem dye-sensitized solar cells (DSSCs). A novel, highly ...

Highly ordered titanium dioxide nanotube (TiO2 NT) arrays were grown by electrochemical anodization of titanium in a molten NH4F/o-H3PO4 electrolyte. NTs with various diameters, lengths, wall thick...

TiO2-based catalyst supports in polymer electrolyte membrane fuel cells (PEMFCs) are widely investigated and provide an alternative to corrosion-susceptible carbon-based catalyst supports. For PEMF...

Photoelectrochemical (PEC) water splitting is a promising method for the conversion of solar energy into chemical energy stored in the form of hydrogen. Nanostructured hematite (α-Fe2 O3 ) is one of the most attractive materials for a highly efficient charge carrier generation and collection due to its large specific surface area and the short minority carrier diffusion length. In the present work, the PEC water splitting performance of nanostructured α-Fe2 O3 is investigated which was prepared by anodization followed by annealing in a low oxygen ambient (0.03 % O2 in Ar). It was found that low oxygen annealing can activate a significant PEC response of α-Fe2 O3 even at a low temperature of 400 °C and provide an excellent PEC performance compared with classic air annealing. The photocurrent of the α-Fe2 O3 annealed in the low oxygen at 1.5 V vs. RHE results as 0.5 mA cm-2 , being 20 times higher than that of annealing in air. The obtained results show that the α-Fe2 O3 annealed in low oxygen contains beneficial defects and promotes the transport of holes; it can be attributed to the improvement of conductivity due to the introduction of suitable oxygen vacancies in the α-Fe2 O3 . Additionally, we demonstrate the photocurrent of α-Fe2 O3 annealed in low oxygen ambient can be further enhanced by Zn-Co LDH, which is a co-catalyst of oxygen evolution reaction. This indicates low oxygen annealing generates a promising method to obtain an excellent PEC water splitting performance from α-Fe2 O3 photoanodes.

Developing ultraefficient electrocatalytic materials for the hydrogen evolution reaction (HER) with low content of expensive platinum group metals (PGMs) via low-energy-input procedures is the key to the successful commercialization of green water electrolysis technologies for sustainable production of high-purity hydrogen. In this study, we report a facile room-temperature synthesis of ultrafine metallic Ir nanoparticles on conductive, proton-intercalated TiO2 nanotube (H-TNT) arrays via galvanic displacement. A series of experiments demonstrate that a controlled transformation of the H-TNT surface microstructure from neat open-top tubes to disordered nanostripe bundles (“nanograss”) is highly beneficial for providing an abundance of exposed Ir active sites. Consequently, for nanograss-engineered composites, outstanding HER activity metrics are achieved even at very low Ir(III) precursor concentrations. An optimum Ir@TNT cathode loaded with 5.7 μgIr cm−2 exhibits an overpotential of −63 mV at −100 mA cm−2 and a mass activity of 34 A mgIr−1 at −80 mV under acidic conditions, along with excellent catalytic durability and structural integrity. Density functional theory (DFT) simulations reveal that the hydrogen-rich TiO2 surface not only stabilizes the deposited Ir and weakens its H binding strength to a moderate intensity, but also actively takes part in the HER mechanism by refreshing the Ir catalytic sites near the Ir|H–TiO2 interface, thus substantially promoting H2 generation. The comprehensive characterization combined with theory provides an in-depth understanding of the electrocatalytic behavior of H-TNT supported PGM nanoparticles and demonstrates their high potential as competitive electrocatalyst systems for the HER.

In electrocatalysis, layered double hydroxide (LDH) materials have attracted considerable interest in promoting the oxygen evolution reaction (OER). For the hydrogen evolution reaction (HER), these materials show a poor electrocatalytic activity. In this work, we take CoFe LDH grown on nickel foam as a model system, and for the first time we treat CoFe LDH under plasma etching conditions, which results in a highly active HER electrocatalyst in alkaline media. Massive defects and amorphous phase formation occur during plasma etching. More importantly, phase transformation of CoFe LDH into CoFe2O4 takes place. Additional introduction of Ce leads to more active sites and improved electrical conductivity, which provide an overpotential of 73 mV at a current density of 10 mA cm−2 for V-Ce/CoFe LDH. The experimental results match well with DFT calculations, proving that defect engineering, phase transformation, and electronic structure tailoring can result in a high efficiency of HER activity. Moreover, a cell constructed of CoFe LDH‖V-Ce/CoFe LDH is capable of overall water splitting with a cell voltage as low as 1.65 V at 10 mA cm−2 and a remarkable long-term stability of 60 h. The plasma etching strategy can also be effective for other LDH-based electrocatalysts (e.g. NiFe LDH and NiCo LDH), which demonstrates the universality of the strategy for improving HER performance. This work provides a simple but feasible pathway for designing alkaline HER electrocatalysts based on advanced LDH materials.

Anodic TiO2 nanotubes that are grown on Ti substrates by a simple anodization in various types of fluoride containing electrolytes have attracted scientific and technological interest due to their wide potential applications, and therefore, numerous research efforts have been dedicated to these self-ordered oxide structures in the past decade. The present mini-review highlights less known but important aspects, such as the formation of spaced nanotubes with adjustable interspacing that is achieved in a few specific organic electrolytes, and strong effects of the metallic Ti substrate which significantly affect the growth of the tubes. We discuss the formation of oxide nanotubes grown from adequately alloyed substrates and noble metal nanoparticle decoration of tubes. We describe how specific heat-treatment can introduce a nanotwinned boundary in the oxide tube walls of single-walled nanotubes obtained by a decoring process. All the facts and findings were studied in recent years and TiO2 nanotubes can be upgraded with more optimized functionalities for their applications.

Recent reports show that Co-Pi cocatalysts on some photoanodes, such as Fe2O3 or BiVO4, accelerate the surface water oxidation rate, acting as a hole extracting layer that improves charge separation or as a “surface passivation agent”. In contrast, on semiconductors such as BiVO4, deposition of classic Co-based oxygen evolution catalysts (e.g. Co3O4, CoOOH) leads to a relatively low improvement of the photoelectrochemical (PEC) performance. This illustrates that even though a species may be an excellent electrocatalyst, it may not be an effective co-catalyst for PEC reactions. Clearly, for different semiconductors there is a need to directly identify and prepare specific, highly active and low-cost cocatalysts for promoting PEC water oxidation. Co(CO3)0.5(OH)·0.11H2O (or in general Co(CO3)xOHy) is usually used as a precursor to synthesize a range of Co-based efficient electrocatalysts. Herein, we for the first time show that Co(CO3)xOHy on BiVO4 provides an excellent oxygen evolution reaction activity, even close to the so far most efficient dual-layer FeOOH/NiOOH cocatalysts. Decoration of BiVO4 with Co(CO3)xOHy and the resulting photoanode shows a remarkable enhancement of photocurrent, achieving a photocurrent density of 5.0 mA cm−2 at 1.23 VRHE with an onset potential of 0.3 VRHE, which is one of the highest PEC activities of BiVO4 reported up to now. The outstanding PEC performance can be attributed to the improvement of charge separation and transfer efficiency caused by a uniform thin coating of Co(CO3)xOHy. The Co(CO3)xOHy exhibits the highest density of active sites, the highest surface area, and the best OER activity among the investigated cobalt-based cocatalysts. Remarkably, the Co(CO3)xOHy also displays a self-healing function in borate buffered electrolytes. Therefore, this work not only describes low-cost but highly active cobalt-based catalysts for PEC solar water oxidation, but additionally shows a self-repair function of this system.