The terminal disulfide and sulfide (S22– and S2–) groups at the edge of layered MoS2 are believed to be highly active toward electrochemical hydrogen evolution reaction (HER). In this work, we prepared a composite of few-layered MoS2 grown on the surface of carbon black (CB). We demonstrated that the ratio of terminal S22– and S2– groups in the obtained MoS2/CB composite depended significantly on the content of CB, which suggests that the activity of the composite toward HER can be tuned by controlling the CB content. The current density on the MoS2/CB catalyst for HER was closely related to the average number of MoS2 layers and the ratio of terminal to total sulfur in the composite, with the former dominating the conductivity of the MoS2 layers and the latter determining the density of active sites for HER. The highest activity and excellent stability were obtained on a MoS2/CB composite with an average of five MoS2 layers and a ratio of terminal to total sulfur of ca. 6.5%. This composite exhibited a current density of 80 mA·cm–2 at −0.225 V vs RHE with a loading of 1.0 mg·cm–2, which is as high as the value reported on the highly active MoS2/graphene catalysts at the same loading. Considering the low cost of commercially available CB and the ease of preparation of the MoS2/CB composite, our MoS2/CB catalyst is highly competitive compared to other MoS2-based catalysts.

As a green and renewable energy source, hydrogen will play a more important role in lessening our reliance on fossil fuels. Electrochemical and photoelectrochemical reduction of water are two critical strategies for sustainable hydrogen production. Exploring low-cost, efficient, and stable catalysts to replace the expensive noble metal-based catalysts for hydrogen evolution reaction (HER) is practically significant in large-scale hydrogen production. In this work, we report the facile synthesis of a novel MoSe2/carbon black (MoSe2/CB) composite with few-layered MoSe2 grown on commercially available carbon black. The obtained MoSe2/CB composite displays a high catalytic activity toward HER in acidic media. The uppermost activity is obtained on the MoSe2/CB composite with a CB percentage of 50% (denoted as MoSe2/CB-50%). The MoSe2/CB-50% catalyst exhibits a current density of 31.5 mA cm–2 at −0.225 V vs RHE and a small Tafel slope of 62 mV dec–1, which is superior to most MoSe2-based catalysts reported previously. Moreover, the MoSe2/CB-50% catalyst also shows an excellent stability for HER during a long-term reaction. In view of the facile preparation, the high activity, good stability, and the low cost of CB, our MoSe2/CB catalyst enables a more prospective application for industrial and renewable hydrogen production as compared to other MoSe2-based catalysts.

We previously reported that the hydrolysis of Ir3+ in homogeneous solution could be triggered by irradiation with light whose energy was larger than a threshold value. In this work, we demonstrated that, by introducing Fe2O3 particles into solution, the incident light energy-restriction for the photo-catalyzed hydrolysis could be broken and the hydrolysis occurred at the Fe2O3/solution interface. The photo-generated holes on the Fe2O3 surface played a key role in oxidizing Ir(III) to Ir(IV) species and triggered the deposition of IrOx. We showed that this photo-catalyzed surface hydrolysis is a universal phenomenon that takes place on the surface of many n-type semiconductors such as Fe2O3, TiO2, and Ag3PO4. As IrOx is an efficient catalyst for oxygen evolution reaction, surface hydrolysis is a general, facile and efficient strategy to prepare semiconductor/IrOx composites, which can be used as anodic materials for photoelectrochemical water splitting.

We report the preparation of CuWO4 nanoflake (NF) array films by using a solid phase reaction method in which WO3 NFs were employed as sacrificial templates. The SEM, TEM and XRD results demonstrated that the obtained CuWO4 films possessed a network structure that was composed of single crystalline NFs intersected with each other. The CuWO4 NF films showed superior photoelectrochemical (PEC) activity to other CuWO4 photoanodes reported recently for the oxygen evolution reaction (OER). We attributed the high activity to the unique morphological and crystalline structure of the CuWO4 film, which enhanced the photoactivity by providing a large specific area, a short hole transport distance from the inside of CuWO4 to the CuWO4/solution interface, and a low grain boundary density. Hydrogen treatment by annealing the CuWO4 NF film in mixed gases of H2 and Ar could further enhance the photoactivity, as hydrogen treatment significantly increased the electron density of CuWO4 by generating oxygen vacancy in the lattice. The photocurrent density for OER obtained on the hydrogen-treated (H-treated) CuWO4 NF film is the largest ever reported on CuWO4 photoanodes in the literature. Moreover, the CuWO4 photoanodes exhibit good stability in weak alkaline solution, while the H-treated CuWO4 photoanodes exhibit acceptable stability. This work not only reveals the potential of CuWO4 as a photoanode material for solar water splitting but also shows that the construction of nanostructured CuWO4 photoanodes is a promising method to achieve high PEC activity toward OER.

A facile electron-charging and reducing method was developed to prepare Au/WO3 nanocomposites for plasmonic solar water splitting. The preparation method involved a charging step in which electrons were charged into WO3 under negative bias, and a subsequent reducing step in which the stored electrons were used to reductively deposit Au on the surface of WO3. The electron-charged WO3 (c-WO3) exhibited tunable reducibility that could be easily controlled by varying the charging parameters, and this property makes this method a universal strategy to prepare metal/WO3 composites. The obtained Au/WO3 nanocomposite showed greatly improved photoactivity toward the oxygen evolution reaction (OER) when compared with WO3. After Au decoration, the OER photocurrent was improved by a percentage of over 80% at low potentials (<0.6 V vs. SCE), and by a percentage of over 30% at high potentials (>1.0 V vs. SCE). Oxygen evolution measurements were performed to quantitatively determine the Faraday efficiency for OER, which reflected the amount of photocurrent consumed by water splitting. The Faraday efficiency for OER was improved from 74% at the WO3 photoanode to 94% at the Au-8/WO3 composite photoanode, and this is the first direct evidence that the Au decoration significantly restrained the anodic side reactions and enhanced the photoelectrochemical (PEC) OER efficiency. The high photoactivity of the composite photoanode toward OER was ascribed to the plasmon resonance energy transfer (PRET) enhancement and the catalytic enhancement of Au nanoparticles (NPs).

Ag/Ag3PO4 composite nanoplate photoanodes were fabricated by electrogeneration of Ag3PO4 on the surface of vertically aligned Ag nanoplates (NPs) in phosphate solution. The outside Ag3PO4 layer acted as a light-absorbing material to generate electron–hole pairs, while the inside Ag NPs acted as both the framework and the electrical connector between Ag3PO4 and the conducting substrate. The obtained composite photoanodes showed a high catalytic activity toward photoelectrochemical (PEC) oxygen evolution reaction (OER). The photoinduced holes reacted with water to generate oxygen on the Ag3PO4 surface, while the photoinduced electrons were efficiently transported to the counter electrode by highly conductive Ag NPs. The Ag/Ag3PO4 composite photoanode exhibited a photocurrent density of 0.25 mA cm−2 at 0.500 V vs. SCE, which is the highest among reported values obtained under conditions similar to this work. The amount of evolved oxygen was monitored to evaluate the percentage of the photocurrent involved in PEC OER, and the Faraday efficiency for PEC OER was obtained to be ca. 95.6%, indicating that most of the photoinduced holes were engaged in OER. The in situ PEC oxidation of Ag to Ag3PO4, which compensated the loss of Ag3PO4 during PEC OER, makes the Ag/Ag3PO4 composite a self-healing system for OER in phosphate solution.

Hydrous iridium oxide (IrOx) nanoparticles (NPs) with an average diameter of 1.7 ± 0.3 nm were prepared via photochemical hydrolysis of iridium chloride in alkaline medium at room temperature. The photoinduced hydrolysis was monitored by time-dependent ultraviolet–visible (UV–vis) spectroscopy, and the effects of the incident wavelength and irradiation time on the production of IrOx NPs were systematically investigated. It was found that UV–vis irradiation is crucial for the generation of IrOx NPs during the hydrolysis of IrCl3, and once the irradiation was turned off, the hydrolysis reaction stopped immediately. The production rate of IrOx NPs greatly depended on the incident wavelength. There is a critical wavelength of 500 nm for the hydrolysis reaction, and IrOx NPs can only be produced under the illumination with an incident wavelength shorter than 500 nm. Moreover, the shorter the incident wavelength, the faster the growth rate of IrOx NPs. The obtained IrOx NPs were highly stable during two months of storage at 4 °C. The Ir/IrOx nanocomposites were prepared by surface reduction of IrOx NPs with NaBH4. The microstructure of the Ir/IrOx composite was characterized by transmission electron microscopy (TEM), and the presence of zero-valence Ir was confirmed by the X-ray diffraction (XRD) result. The Ir/IrOx nanocomposite exhibited good catalytic activity and high recycling stability toward the reduction of 4-nitrophenol. The catalytic activity per unit surface area of the Ir/IrOx composite catalyst was increased by a factor of 15 compared to that of pure Ir catalyst. The presence of the Ir/IrOx interfaces in the composite catalyst is believed to be responsible for the high activity.Keywords: 4-nitrophenol; catalysis; iridium oxide; nanocomposite; photochemistry

•Hemispherical Au nanoparticles (AuNPs) were prepared on ITO by CV method.•Pre-deposition of Au nanoseeds was a prerequisite for uniform growth of AuNPs.•AuNPs underwent a cycle-by-cycle growth during CV sweep.•The higher the potential scan rate, the lower the one-cycle-growth rate of AuNPs.•CV technique provides a powerful tool to control the particle size.A simple two-step approach, which combines the seeded growth strategy and the cyclic voltammetric (CV) growth technique, has been developed to prepare hemispherical gold nanoparticles (Au NPs) on indium tin oxides (ITO) substrates. Au nanoseeds that were pre-deposited on ITO surface by pulse chronoamperometry have successfully served as nuclei for the following CV growth of Au NPs. The rapid alternation of the anodic and cathodic potential sweep during CV growth has greatly promoted the isotropic growth of Au NPs. The factors that have great effects on the size and growth rate of the Au NPs during CV growth were systematically investigated. The particle size increases monotonically with increasing the number of CV cycles, and the particles undergo a clear cycle-by-cycle growth mechanism, which provides a powerful tool to control the particle size by simply varying the number of CV cycles. The average one-cycle-growth rate of Au NPs was determined by the scan rate of CV measurements, and the higher the scan rate, the lower the growth rate. The scan-rate-dependent growth rate provides another powerful tool to modulate the growth rate by varying the potential scan rate. A average one-cycle-growth rate of ca. 0.94 nm was obtained at scan rate of 400 mV ∙ s− 1, and monodisperse Au NPs with diameters from 45 to around 300 nm and a narrow size distribution have been successfully prepared on ITO substrates. The obtained Au NP modified electrodes exhibited high activity toward CO electrooxidation.

Vertically aligned Ag nanoplates (NPs) were fabricated on indium tin oxide (ITO) substrates by electrodeposition growth in the AgNO3 solution using citrate anions as the shape-controlling agent. The factors affecting the deposition process, such as the potentials applied to the ITO substrate and the concentration of the precursors and citrate, were systematically investigated. We found that the potentials applied both for nucleus generation and for nucleus growth play important roles in tuning the morphology of the Ag NPs. It was also found that the concentration ratio of capping agent to precursor (R) is a critical factor; only when R is relatively low (R < 1.0) could the well-aligned Ag NPs be formed. However, a high R value will lead to the isotropic growth of the Ag crystal. A concentration-gradient-induced growth mechanism of vertically aligned Ag NPs is proposed on the basis of experimental results obtained. A Ag NPs/Ag3PO4 composite electrode was fabricated by a electrodeposition method. The photoelectrochemical oxygen evolution reaction activity of the Ag NPs/Ag3PO4 electrode is about 15.6 times higher than that of a control electrode, which was fabricated on the basis of a Ag electrode whose morphology was irregular polyhedrons.

•CuO films were prepared for photoelectrochemical (PEC) hydrogen evolution reaction (HER).•The photoactivity of CuO decreases significantly with increasing reaction time.•CuO can be reduced to Cu2O by photo-induced electrons during PEC HER.•Deposition of Pd on CuO improves the photoactivity toward HER.•The CuO/Pd composite exhibits superior photostability to CuO.CuO has been considered as a promising photocathodic material for photoelectrochemical (PEC) hydrogen evolution reaction (HER). In this work, CuO films were prepared by a facile and cost-effective method that involves solution synthesis, spin-coating and thermal treatment processes. The resulting CuO films had a monoclinic crystal structure with bandgap energy of 1.56 eV and a conduction band position of 3.73 eV below the vacuum level in borate buffer solution. The CuO films exhibited good PEC activity toward HER and the preparation conditions had great effect on the activity. The photoactivity of the CuO film decayed to approximately 19% of its original value after reaction for 10 h under illumination. The reduction of CuO to Cu2O has been confirmed to be a parallel competitive reaction against HER. The mismatched band structure of the resulting CuO/Cu2O heterojunction was believed to be the main cause of the decay of photoactivity. The photo-assisted electrodeposition method was developed to prepare CuO/Pd composite photocathode. The presence of Pd on CuO greatly increased the photocurrent especially at low overpotentials. In addition, the CuO/Pd composite exhibited significantly improved photostability compared to CuO. This work demonstrates the feasibility of increasing PEC activity and stability of CuO-based photocathodes by combining CuO with noble metal nanoparticles.

Vertically aligned Pd nanoneedles (NNs) with high aspect ratio and uniform growth density were fabricated on indium tin oxide (ITO) substrates by a facile electrodeposition method, which consisted of a short nanoseed-generating step followed by a growth step. The obtained Pd NNs have a full width at half-maximum (fwhm) of 22 ± 8 nm and taper angle of 15 ± 4°. X-ray diffraction (XRD) and high-resolution transmission electron microscopic (HRTEM) results imply that the NNs were built through the stacking of {111} facets. The factors influencing the electrochemical nucleation and growth of Pd NNs were systematically studied. It was found that the transient nucleation step at a highly negative overpotential is prerequisite to the formation of the uniformly dispersed and vertically aligned Pd NNs. The morphology, size, and aspect ratio of Pd nanocrystals (NCs) were extremely sensitive to the potential applied in the growth step. High aspect ratio and well-aligned Pd NNs could only be obtained in a narrow potential range from 0.100 to 0.200 V. Bromide ions played a dominant role in shaping the morphology of Pd NCs, while citrate ions acted as an assistant shape-controlling agent. A concentration-gradient-induced growth mechanism of Pd NNs was proposed on the basis of the time-dependent scanning electron microscopic (SEM) results. The formation of a uniform diffusion layer at the Pd NNs/solution interface and the concentration gradient of the precursor within the diffusion layer were responsible for the vertically oriented growth of Pd NNs. The Pd NNs exhibited good surface-enhanced Raman scattering (SERS) activity under the excitation of 488 nm laser, implying its potential application as a SERS substrate. The SERS activity of Pd NNs was attributed to the unique morphology and the perpendicular alignment of Pd NNs.

•WO3 nanoneedles were grown on FTO substrates for solar water oxidation.•Nickel-borate (Ni-Bi) was used as oxygen-evolving catalyst to modify WO3 nanoneedles.•Deposition of Ni-Bi on WO3 nanoneedles improves the activity toward O2 evolution reaction.•WO3 nanoneedles/Ni-Bi composites show superior photostability to WO3 nanoneedles.Oxygen evolution reaction (OER) is the key process for solar powered water-splitting. In this work, we report the fabrication of the WO3 nanoneedles/nickel-borate composite photoanodes for efficient photoelectrochemical OER, with the high-aspect-ratio nanoneedles as light-absorbing material and the nickel-borate (Ni-Bi) as oxygen-evolving catalyst. We demonstrate that the combination of Ni-Bi with WO3 nanoneedles significantly enhances the activity of the photoanode toward OER by negatively shifting the onset potential of the photocurrent and improving the photocurrent within the entire oxygen-evolving potential region. Moreover, the WO3 nanoneedles/Ni-Bi composite photoanodes exhibit superior stability to the WO3 nanoneedles photoanodes in borate buffer solution at all oxygen-evolving potentials. The present result offers promising opportunities for using Ni-Bi as an oxygen-evolving catalyst to modify semiconductor photoanode to improve solar-to-oxygen efficiency.

The rhodium nanoparticles (RhNPs) were prepared in aqueous, ethanol, and water–ethanol mixed solution using rhodium chloride, sodium borohydride and polyvinylpyrrolidone (PVP) as precursor, reducing agent and stabilizer, respectively. The effect of solvent polarity on the assembly behavior of PVP coated RhNPs was systematically investigated by varying the water-to-ethanol ratio in the solution. The main product changed from small separated RhNPs in ethanol to large spherical assemblies of RhNPs in water. The strong tendency for the RhNPs to form aggregates in high polarity solvent was clearly demonstrated by increasing the water-to-ethanol ratio in the reaction media. TEM characterization revealed a two-step formation process of the spherical RhNP assemblies in water: the initial rapid particle generation step followed by a slow particle aggregation step. A mechanism was proposed to elucidate the aggregation behavior of PVP coated RhNPs. The driving force for the aggregation of RhNPs is ascribed to the hydrophobic interaction of hydrocarbon chains of PVP, which can greatly reduce the surface energy of PVP coated RhNPs in high polarity solvents. This work shed light on how to control the formation of nanoparticle aggregates by modulating the polarity of solvent.Highlights ► The solvent polarity effect on the assembly of Rh nanoparticles (RhNPs) was investigated. ► Discrete RhNPs and spherical aggregates were obtained in ethanol and water, respectively. ► RhNPs tended to form spherical assemblies with increasing solvent polarity. ► A particle generation step followed by an assembly step was observed in high-polar solvents. ► A mechanism was proposed to elucidate the assembly behavior of RhNPs.

Standing rhodium nanoplates were successfully synthesized on indium tin oxide (ITO) substrate by electrochemical deposition using RhCl3 and sodium citrate as precursor and capping agent, respectively. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed that most of the Rh nanoplates are perpendicularly orientated to the ITO substrate with an average length of 140 nm, an average height of 120 nm, and a thickness of 25 nm. X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicated that the standing Rh nanoplates (s-RhNPs) were single crystals with face-centered cube pattern. The factors influencing the electrochemical growth of Rh nanocrystals (RhNCs) were systematically studied. It was found that the transient nucleation step at a high overpotential before electrochemical growth is crucial to the formation of a uniform s-RhNPs array. The morphology of RhNCs is very sensitive to the applied growth potential and s-RhNPs can only be obtained in a narrow potential range of −0.240 to −0.260 V. Moreover, the concentrations of both the precursor (RhCl3) and the capping agent (sodium citrate) have significant effect on the morphology of RhNCs. A mechanism was proposed to explain the electrochemical growth and orientation of s-RhNPs. Electrocatalyic measurements demonstrated that the as-synthesized s-RhNPs, compared with isotropic RhNCs, exhibit higher catalytic current density for formic acid electrooxidation.

A dual-region modified electrode was designed and fabricated by means of partitioned electrodeposition of gold and platinum nanoparticles on an indium tin oxide (ITO) conductive glass for dual-component electrochemical detection. The two differently modified regions were assigned to detect two analytes, separately and simultaneously. The gold nanoparticle modified ITO region (AuNPs/ITO) was used for glucose detection while the platinum nanoparticle modified ITO region (PtNPs/ITO) for nitrite detection. The glucose oxidation peak current at 0.10 V on AuNPs/ITO exhibited a linear dependence on the concentration of glucose and was used to determine the concentration of glucose in dual-detection. The nitrite reduction peak current at PtNPs/ITO showed a nonlinear dependence on the concentration of nitrite. A theoretical model combining the adsorption-controlled and the mass-transfer-controlled kinetics was proposed to quantitatively describe the nonlinear behavior. Though the presence of glucose interfered with the electrochemical detection of nitrite, it was demonstrated that the influence of glucose on nitrite detection can be corrected. On the basis of the proposed theoretical model, the simultaneous dual-detection of glucose and nitrite was accomplished at ITO electrodes partitionally modified with AuNPs and PtNPs.

Iridium nanoparticles (IrNPs) and submicroparticles (IrSMPs) with different shapes were synthesized and assembled on indium thin oxide (ITO) and Si substrates using two different methods: direct surface growth and drop-drying assembly. The obtained IrNPs and IrSMPs were characterized using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The IrSMPs (or IrNPs) with disc-like shape and irregular shapes were obtained on ITO substrate by direct surface growth method using polyvinylpyrrolidone (PVP) and sodium citrate as different stabilizers, respectively. The reaction time and the injection temperature of reducing agent are found to have great effect on the size and morphology of the surface-grown Ir particles. The disc-like, ellipsoidal, and spherical IrSMPs (or IrNPs) were also synthesized in homogeneous solution in the presence of H3BO3 and Na2B4O7 as assistant-stabilizer. These IrNPs and IrSMPs were used as building blocks to construct nanoparticle assemblies by using a simple drop-drying method. Uniform IrNP and IrSMP assemblies were successfully prepared on Si and ITO substrates, indicating that the drop-drying method is efficient for the preparation of not only nanoparticle assemblies but also submicroparticle assemblies.

An enzyme-free electrode was fabricated by anodic electrodeposition of cobalt oxyhydroxide film on an ITO electrode (CoOx(OH)y/ITO) for direct electrochemical detection of pyruvic acid (PA) in solution. Scanning electron microscopy (SEM) and atom force microscopy (AFM) were employed to characterize the morphology of CoOx(OH)y film. Cyclic voltammetry (CV) was used to investigate the electrochemical properties of PA on CoOx(OH)y/ITO in order to select the optimal potential for the chronoamperometric detection of PA. It was found that the CoOx(OH)y/ITO electrode served as an excellent PA sensor with a linear detection range of 1.00 μM to 1.91 mM, a detection limit of 0.55 μM, and a high sensitivity of 417.1 μA mM−1 cm−2. Moreover, the response time of CoOx(OH)y/ITO to PA is less than 10 s, which is the shortest for PA detection reported in literature using electrochemical method. These properties and the high stability of CoOx(OH)y/ITO made it a good candidate for developing electrochemical enzyme-free PA sensing device.

The gold nanoparticles (AuNPs) sputtered on indium tin oxide (ITO) were used to investigate the origin of the high catalytic activity of AuNPs toward electrooxidation of CO in alkali media. We demonstrated that the catalytic activity is closely related to the gold–ITO perimeter, which represents only a very small percentage of the total surface area of AuNPs. Increasing the perimeter-to-surface ratio of the ITO-supported AuNPs leads to an increase of catalytic activity. This work provides a potential strategy to further promote the catalytic activity of AuNPs in the electrochemical system.

The gold submicroparticles (AuSMPs) electrodeposited on indium tin oxide (ITO) were used to develop an electrochemical method for determining the concentration of CO in gas phase. We demonstrated that the peak current for CO oxidation in cyclic voltammetry (CV) is proportionally dependent on the gas phase concentration of CO. Experimental results are in good agreements with the theoretical predictions over a wide concentration regime, providing a solid foundation for the quantitatively sensing of CO at AuSMPs/ITO electrodes.

A well-defined potential gradient was introduced to the surface of indium tin oxide (ITO) during the seed-mediated synthesis of anisotropic gold nanoparticles (AuNPs) on substrates. Benefiting from this potential gradient, we found an evolution of particle morphology as a function of the position potential on ITO substrates. With increasing potential, gold triangular nanoprisms and triangular, hexagonal, and polygonal nanoplates were successively produced as the main products. The results obtained in a traditional three-electrode cell demonstrated a similar morphology evolution trend, confirming that substrate potential is one of the key factors controlling the morphology of nanoparticles. The different adsorption behavior of capping agents on gold facets under different potentials was believed to be the cause of the potential-induced particle morphology evolution. This work offers opportunities for potential-assisted shape-selective synthesis of nanoparticles on conducting substrates.

Alkanethiol monolayers were formed on gold at different potentials by a potential-controlled assembly procedure, which involves (1) reductive desorption of the pre-adsorbed thiol molecules to “clean” the gold surface, and (2) subsequent electrochemically directed adsorption of thiol molecules at positive potentials. The dependence of the monolayer integrity on the substrate potential was investigated using grazing incidence reflection–absorption Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). It is demonstrated that the substrate potential exerts a great effect on the quality of alkanethiol monolayers. The monolayers formed at ≈0.4 V (vs SCE) have the best film integrity. A mechanism is proposed to explain the effect of substrate potential on the film quality. This work provides solid basis for the selection of adsorption potentials in potential-controlled formation of organic layers on solid surfaces.

We investigated the catalytic activity of gold particles toward CO electrooxidation by cyclic voltammetry and found that the formation of oxidic gold species on the surface of gold nanoparticles (AuNPs) is a necessary condition for electrooxidation of CO. The maximum potential in the positive-going sweep has a great effect on the formation of gold oxides as well as on the activity of AuNPs. We report the support-dependent electrooxidation of CO in aqueous solution as the first example of the contribution of the support to the high catalytic activity of AuNPs in electrochemical systems. We also show that particle size, reported to be a dominant factor in the catalytic oxidation of CO on AuNPs in solid–gas reaction systems, is no longer a critical factor controlling the activity of AuNPs in electrochemical systems. We demonstrate that indium tin oxide-supported gold submicroparticles, which are believed to be catalytically inactive due to their “large” size, exhibit surprisingly high activity toward electrooxidation of CO.

We previously reported that the hydrolysis of Ir3+ in homogeneous solution could be triggered by irradiation with light whose energy was larger than a threshold value. In this work, we demonstrated that, by introducing Fe2O3 particles into solution, the incident light energy-restriction for the photo-catalyzed hydrolysis could be broken and the hydrolysis occurred at the Fe2O3/solution interface. The photo-generated holes on the Fe2O3 surface played a key role in oxidizing Ir(III) to Ir(IV) species and triggered the deposition of IrOx. We showed that this photo-catalyzed surface hydrolysis is a universal phenomenon that takes place on the surface of many n-type semiconductors such as Fe2O3, TiO2, and Ag3PO4. As IrOx is an efficient catalyst for oxygen evolution reaction, surface hydrolysis is a general, facile and efficient strategy to prepare semiconductor/IrOx composites, which can be used as anodic materials for photoelectrochemical water splitting.

Ag/Ag3PO4 composite nanoplate photoanodes were fabricated by electrogeneration of Ag3PO4 on the surface of vertically aligned Ag nanoplates (NPs) in phosphate solution. The outside Ag3PO4 layer acted as a light-absorbing material to generate electron–hole pairs, while the inside Ag NPs acted as both the framework and the electrical connector between Ag3PO4 and the conducting substrate. The obtained composite photoanodes showed a high catalytic activity toward photoelectrochemical (PEC) oxygen evolution reaction (OER). The photoinduced holes reacted with water to generate oxygen on the Ag3PO4 surface, while the photoinduced electrons were efficiently transported to the counter electrode by highly conductive Ag NPs. The Ag/Ag3PO4 composite photoanode exhibited a photocurrent density of 0.25 mA cm−2 at 0.500 V vs. SCE, which is the highest among reported values obtained under conditions similar to this work. The amount of evolved oxygen was monitored to evaluate the percentage of the photocurrent involved in PEC OER, and the Faraday efficiency for PEC OER was obtained to be ca. 95.6%, indicating that most of the photoinduced holes were engaged in OER. The in situ PEC oxidation of Ag to Ag3PO4, which compensated the loss of Ag3PO4 during PEC OER, makes the Ag/Ag3PO4 composite a self-healing system for OER in phosphate solution.