Ti3+-Promoted High Oxygen-Reduction Activity of Pd Nanodots Supported by Black Titania Nanobelts

Recent Progress in the Design and Application of Strong Metal-Support Interactions in Electrocatalysis

The strong metal-support interaction (SMSI) in supported metal catalysts represents a crucial factor in the design of highly efficient heterogeneous catalysts. This interaction can modify the surface adsorption state, electronic structure, and coordination environment of the supported metal, altering the interface structure of the catalyst. These changes serve to enhance the catalyst's activity, stability, and reaction selectivity. In recent years, a multitude of researchers have uncovered a range of novel SMSI types and induction methods including oxidized SMSI (O-SMSI), adsorbent-mediated SMSI (A-SMSI), and wet chemically induced SMSI (Wc-SMSI). Consequently, a systematic and critical review is highly desirable to illuminate the latest advancements in SMSI and to deliberate its application within heterogeneous catalysts. This article provides a review of the characteristics of various SMSI types and the most recent induction methods. It is concluded that SMSI significantly contributes to enhancing catalyst stability, altering reaction selectivity, and increasing catalytic activity. Furthermore, this paper offers a comprehensive review of the extensive application of SMSI in the electrocatalysis of hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and carbon dioxide reduction reaction (CO2RR). Finally, the opportunities and challenges that SMSI faces in the future are discussed.

Enhanced performance of photocatalytic oxidation of indoor toluene over Pd/TiO2 catalyst by tuning surface defect concentrations

An effective approach for the elimination of indoor gaseous toluene through photocatalytic oxidation involves the engineering of surface defects on catalysts. In this study, the concentrations of surface oxygen defects in PdTi-xN (x = 10, 30) catalysts were controlled using the sodium borohydride solid-phase reduction method, and their performances in the photocatalytic oxidation of indoor gaseous toluene were evaluated. PdTi-10 N demonstrated high photocatalytic efficiency for toluene oxidation, achieving 84% toluene conversion and approximately 75% CO2 mineralization. Characterization results indicated that surface oxygen defects can enhance the separation of photo-generated electrons and holes, facilitating their interaction with Pd0 species to form Ti3+ species. More reactive oxygen species (·OH-and ·O2-) were generated on PdTi-10 N due to the synergistic effect of surface oxygen defect and Ti3+ species, which played a significant role as the toluene oxidation. This work provides a new insight for the design and development of high-performance Pd/TiO2 catalysts in the field of indoor VOCs treatment.

Component-controlled synthesis of PdxSny nanocrystals on carbon nanotubes as advanced electrocatalysts for oxygen reduction reaction

Pd-based bimetallic or multimetallic nanocrystals are considered to be potential electrocatalysts for cathodic oxygen reduction reaction (ORR) in fuel cells. Although much advance has been made, the synthesis of component-controlled Pd-Sn alloy nanocrystals or corresponding nanohybrids is still challenging, and the electrocatalytic ORR properties are not fully explored. Herein, component-controlled synthesis of PdxSny nanocrystals (including Pd3Sn, Pd2Sn, Pd3Sn2, and PdSn) has been realized, which are in situ grown or deposited on pre-treated multi-walled carbon nanotubes (CNTs) to form well-coupled nanohybrids (NHs) by a facile one-pot non-hydrolytic system thermolysis method. In alkaline media, all the resultant PdxSny/CNTs NHs are effective at catalyzing ORR. Among them, the Pd3Sn/CNTs NHs exhibit the best catalytic activity with the half-wave potential of 0.85 V (vs. RHE), good cyclic stability, and excellent methanol-tolerant capability due to the suited Pd-Sn alloy component and its strong interaction or efficient electronic coupling with CNTs. This work is conducive to the advancement of Pd-based nanoalloy catalysts by combining component engineering and a hybridization strategy and promoting their application in clean energy devices.

Constructing an oxygen vacancy- and hydroxyl-rich TiO2-supported Pd catalyst with improved Pd dispersion and catalytic stability

Surface property modification of catalyst support is a straightforward approach to optimize the performance of supported noble metal catalysts. In particular, oxygen vacancies and hydroxyl groups play significant roles in promoting noble metal dispersion on catalysts as well as catalytic stability. In this study, we developed a nanoflower-like TiO2-supported Pd catalyst that has a higher concentration of oxygen vacancies and surface hydroxyl groups compared to that of commercial anatase and P25 support. Notably, due to the distinctive structure of the nanoflower-like TiO2, our catalyst exhibited improved dispersion and stabilization of Pd species and the formation of abundant reactive oxygen species, thereby facilitating the activation of CO and O2 molecules. As a result, the catalyst showed remarkable efficiency in catalyzing the low-temperature CO oxidation reaction with a complete CO conversion at 80 °C and stability for over 100 h.

Adsorption Energy in Oxygen Electrocatalysis

Adsorption energy (AE) of reactive intermediate is currently the most important descriptor for electrochemical reactions (e.g., water electrolysis, hydrogen fuel cell, electrochemical nitrogen fixation, electrochemical carbon dioxide reduction, etc.), which can bridge the gap between catalyst's structure and activity. Tracing the history and evolution of AE can help to understand electrocatalysis and design optimal electrocatalysts. Focusing on oxygen electrocatalysis, this review aims to provide a comprehensive introduction on how AE is selected as the activity descriptor, the intrinsic and empirical relationships related to AE, how AE links the structure and electrocatalytic performance, the approaches to obtain AE, the strategies to improve catalytic activity by modulating AE, the extrinsic influences on AE from the environment, and the methods in circumventing linear scaling relations of AE. An outlook is provided at the end with emphasis on possible future investigation related to the obstacles existing between adsorption energy and electrocatalytic performance.

Hexagonal BaTiO(3-x)Hx Oxyhydride as a Water-Durable Catalyst Support for Chemoselective Hydrogenation

We present heavily H^--doped BaTiO_(3-x)H_x (x ≈ 1) as an efficient and water-durable catalyst support for Pd nanoparticles applicable to liquid-phase hydrogenation reactions. The BaTiO_(3-x)H_x oxyhydride with a hexagonal crystal structure (P6₃/mmc) was synthesized by the direct reaction of BaH₂ and TiO₂ at 800 °C under a stream of hydrogen, and the estimated chemical composition was BaTiO_2.01H_0.96. Density functional theory calculations and magnetic measurements indicated that such heavy H^- doping results in a metallic nature with delocalized electrons and a low work function. The potential of BaTiO_(3-x)H_x as a catalyst support was examined for the selective hydrogenation of unsaturated C-C bonds by Pd nanoparticles deposited on BaTiO_(3-x)H_x. We found that the turnover frequency for phenylacetylene hydrogenation per total amount of Pd in Pd/BaTiO_(3-x)H_x was the highest among the supported Pd catalysts reported to date. The strong electronic charge transfer between Pd and the support, as confirmed by X-ray photoelectron spectroscopy measurements, can be attributed to be responsible for such high catalytic activity. The combination of the BaTiO_(3-x)H_x support and Pd nanoparticles provides for the selective hydrogenation of unsaturated C-C bonds and highlights the validity of catalyst design that integrates H^- in support materials.

Recent Advances in Electrocatalysts for Proton Exchange Membrane Fuel Cells and Alkaline Membrane Fuel Cells

The rapid progress of proton exchange membrane fuel cells (PEMFCs) and alkaline exchange membrane fuel cells (AMFCs) has boosted the hydrogen economy concept via diverse energy applications in the past decades. For a holistic understanding of the development status of PEMFCs and AMFCs, recent advancements in electrocatalyst design and catalyst layer optimization, along with cell performance in terms of activity and durability in PEMFCs and AMFCs, are summarized here. The activity, stability, and fuel cell performance of different types of electrocatalysts for both oxygen reduction reaction and hydrogen oxidation reaction are discussed and compared. Research directions on the further development of active, stable, and low-cost electrocatalysts to meet the ultimate commercialization of PEMFCs and AMFCs are also discussed.

Galvanic Deposition of Pt Nanoparticles on Black TiO2 Nanotubes for Hydrogen Evolving Cathodes

A galvanic deposition method for the in-situ formation of Pt nanoparticles (NPs) on top and inner surfaces of high-aspect-ratio black TiO2 -nanotube electrodes (bTNTs) for true utilization of their total surface area has been developed. Density functional theory calculations indicated that the deposition of Pt NPs was favored on bTNTs with a preferred [004] orientation and a deposition mechanism occurring via oxygen vacancies, where electrons were localized. High-resolution transmission electron microscopy images revealed a graded deposition of Pt NPs with an average diameter of around 2.5 nm along the complete nanotube axis (length/pore diameter of 130 : 1). Hydrogen evolution reaction (HER) studies in acidic electrolytes showed comparable results to bulk Pt (per geometric area) and Pt/C commercial catalysts (per mg of Pt). The presented novel HER cathodes of minimal engineering and low noble metal loadings (μg cm-2 range) achieved low Tafel slopes (30-34 mV dec-1 ) and high stability in acidic conditions. This study provides important insights for the in-situ formation and deposition of NPs in high-aspect-ratio structures for energy applications.

Greatly Facilitated Two-Electron Electroreduction of Oxygen into Hydrogen Peroxide over TiO2 by Mn Doping

Ambient electrochemical oxygen reduction into valuable hydrogen peroxide (H₂O₂) via a selective two-electron (2e^-) pathway is regarded as a sustainable alternative to the industrial anthraquinone process, but it requires advanced electrocatalysts with high activity and selectivity. In this study, we report that Mn-doped TiO₂ behaves as an efficient electrocatalyst toward highly selective H₂O₂ synthesis. This catalyst exhibits markedly enhanced 2e^- oxygen reduction reaction performance with a low onset potential of 0.78 V and a high H₂O₂ selectivity of 92.7%, much superior to the pristine TiO₂ (0.64 V, 62.2%). Additionally, it demonstrates a much improved H₂O₂ yield of up to 205 ppm h^-1 with good stability during bulk electrolysis in an H-cell device. The significantly boosted catalytic performance is ascribed to the lattice distortion of Mn-doped TiO₂ with a large amount of oxygen vacancies and Ti³⁺. Density functional theory calculations reveal that Mn dopant improves the electrical conductivity and reduces ΔG_*OOH of pristine TiO₂, thus giving rise to a highly efficient H₂O₂ production process.

Enhancing the Catalytic Activity of Palladium Nanoparticles via Sandwich-Like Confinement by Thin Titanate Nanosheets

As atomically thin oxide layers deposited on flat (noble) metal surfaces have been proven to have a significant influence on the electronic structure and thus the catalytic activity of the metal, we sought to mimic this architecture at the bulk scale. This could be achieved by intercalating small positively charged Pd nanoparticles of size 3.8 nm into a nematic liquid crystalline phase of lepidocrocite-type layered titanate. Upon intercalation the galleries collapsed and Pd nanoparticles were captured in a sandwichlike mesoporous architecture showing good accessibility to Pd nanoparticles. On the basis of X-ray photoelectron spectroscopy (XPS) and CO diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) Pd was found to be in a partially oxidized state, while a reduced Ti species indicated an electronic interaction between nanoparticles and nanosheets. The close contact of titanate sandwiching Pd nanoparticles, moreover, allows for the donation of a lattice oxygen to the noble metal (inverse spillover). Due to the metal-support interactions of this peculiar support, the catalyst exhibited the oxidation of CO with a turnover frequency as high as 0.17 s-1 at a temperature of 100 °C.

Constructing porous TiO2 crystals by an etching process for long-life lithium ion batteries

"Zero strain" materials, which have no volume change when charging and discharging, show ultra-long cycling stabilities when used as lithium-ion battery anodes, making them an area of extreme interest in this decade. For a typical anatase TiO₂ crystal, the volume change is 3-4% during Li insertion/extraction, which is not "zero strain". As the Ti/O packing in the TiO₂ lattice is too tight, there is insufficient void space for Li insertion, leading to volume expansion and structural collapse. Herein, pseudo-"zero-strain" TiO₂ is achieved via designing TiO₂ crystals with abundant inner mesopores, making Ti/O loose-packed via the acid-etching of K₂Ti₈O₁₇, providing sufficient space for Li intercalation. Instead of the traditional cut-off potential of 1 V used for Ti-/Nb-based anodes, we choose 0.01 V as the cut-off to make the best of the extra capacity contributed by the mesopores. As expected, plenty of mesopores could serve as "Li⁺-reservoirs" for fast lithium storage, demonstrating exceptional high-rate performance with an average capacity of 109.6 mA h g^-1 after 30 000 cycles at 60 C and 100 mA h g^-1 at 120 C. Such a strategy of combining a mesoporous structure and cut-off potential regulation may pave a solid pathway for constructing novel high-power anodes.

Niobium dioxide prepared by a novel La-reduced route as a promising catalyst support for Pd towards the oxygen reduction reaction

Electron transfer from NbO₂ to Pd enhances the ORR activity of Pd/NbO₂.

Yolk-Shell Fe/Fe4 N@Pd/C Magnetic Nanocomposite as an Efficient Recyclable ORR Electrocatalyst and SERS Substrate

A yolk-shell Fe/Fe₄ N@Pd/C (FFPC) nanocomposite is synthesized successfully by two facile steps: interfacial polymerization and annealing treatment. The concentration of Pd²⁺ is the key factor for the density of Pd nanoparticles (Pd NPs) embedded in the carbon shells, which plays a role in the oxygen reduction reaction (ORR) and surface-enhanced Raman scattering (SERS) properties. The ORR and SERS performances of FFPC nanocomposites under different concentrations of PdCl₂ are investigated. The optimal ORR performance exhibits that onset potential and tafel slope can reach 0.937 V (vs reversible hydrogen electrode (RHE)) and 74 mV dec^-1 , respectively, which is attributed to the synergistic effects of good electrical conductivity, large electrochemically active areas, and strong interfacial charge polarization. Off-axis electron holography reveals that interfacial charge polarization could facilitate the ORR of Pd NPs and defective carbon simultaneously and the shell with low density of Pd NPs is easier to form strong interfacial charge polarization. Moreover, FFPC-3 with maximum EF of 2.3 × 10⁵ results from more hot-spots, local positive charge centers to attract rhodamine 6G molecules, and magnetic cores. This work not only offers a recyclable multifunctional nanocomposite with excellent performance, but also has instructional implications for interfacial engineering for electrocatalysts design.

Engineering of highly active Au/Pd supported on hydrogenated urchin-like yolk@shell TiO2 for visible light photocatalytic Suzuki coupling

An engineered hydrogenated urchin-like yolk@shell TiO₂ structure decorated with Au/Pd nanoparticles was designed via sequential steps and employed in visible light photocatalytic Suzuki coupling.

Constructing a novel strategy for controllable synthesis of corrosion resistant Ti3+ self-doped titanium-silicon materials with efficient hydrogen evolution activity from simulated seawater

Exploiting solar power for hydrogen production from seawater is a great challenge owing to the corrosive properties of seawater and inadequate visible-light conversion capabilities. Here we report an uncomplicated post-processing method to construct Ti³⁺ self-doped titanium-silicon material with corrosion resistance. This is a new experimental method to regulate the electrical, optical, and photocatalytic performances of titanium-containing photocatalysts in a controlled way. Moreover, we demonstrate that Ti-O-Si materials with different calcination temperatures can serve as a highly efficient and convenient catalyst for photogeneration of hydrogen from water and simulated seawater. Consequently, the optimized Ti-O-Si (400) sample exhibits impressive enhancement in the photocatalytic hydrogen evolution performance, by nearly 10.0 and 43.1 times compared with TiO₂ nanoparticles in water and simulated seawater. The Ti-O-Si (400) with substantial Ti³⁺ and oxygen vacancies exhibits an excellent photocatalytic H₂ production performance due to the improved separation and transmission of the photogenerated electron-hole, the extended visible light response, and corrosion resistance. Our work opens a new door to engineering the intrinsic properties of the titanium-containing materials.

Oxygen-Induced Bi5+-Self-Doped Bi4V2O11 with a p-n Homojunction Toward Promoting the Photocatalytic Performance

Bi⁵⁺-self-doped Bi₄V₂O₁₁ (Bi⁵⁺-BVO) nanotubes with p-n homojunctions are fabricated via an oxygen-induced strategy. Calcinating the as-spun fibers with abundant oxygen plays a pivotal role in achieving Bi⁵⁺ self-doping. Density functional theory calculations and experimental results indicate that Bi⁵⁺ self-doping can narrow the band gap of Bi₄V₂O₁₁, which contributes to enhancing light harvesting. Moreover, Bi⁵⁺ self-doping endows Bi₄V₂O₁₁ with n- and p-type semiconductor characteristics simultaneously, resulting in the construction of p-n homojunctions for retarding rapid electron-hole recombination. Benefiting from these favorable properties, Bi⁵⁺-BVO exhibits a superior photocatalytic performance in contrast to that of pristine Bi₄V₂O₁₁. Furthermore, this is the first report describing the achievement of p-n homojunctions through self-doping, which gives full play to the advantages of self-doping.