PtIr/Ti4O7 as a bifunctional electrocatalyst for improved oxygen reduction and oxygen evolution reactions

Recent advances in synthesis and application of Magnéli phase titanium oxides for energy storage and environmental remediation

High-temperature reduction of TiO2 causes the gradual formation of structural defects, leading to oxygen vacancy planar defects and giving rise to Magnéli phases, which are substoichiometric titanium oxides that follow the formula Ti n O2n-1, with 4 ≤ n ≤ 9. A high concentration of defects provides several possible configurations for Ti4+ and Ti3+ within the crystal, with the variation in charge ordered states changing the electronic structure of the material. The changes in crystal and electronic structures of Magnéli phases introduce unique properties absent in TiO2, facilitating their diverse applications. Their exceptional electrical conductivity, stability in harsh chemical environments and capability to generate hydroxyl radicals make them highly valuable in electrochemical applications. Additionally, their high specific capacity and corrosion resistance make them ideal for energy storage facilities. These properties, combined with excellent solar light absorption, have led to their widespread use in electrochemical, photochemical, photothermal, catalytic and energy storage applications. To provide a complete overview of the formation, properties, and environmental- and energy-related applications of Magnéli phase titanium suboxides, this review initially highlights the crystal structure and the physical, thermoelectrical and optical properties of these materials. The conventional and novel strategies developed to synthesise these materials are then discussed, along with potential approaches to overcome challenges associated with current issues and future low-energy fabrication methods. Finally, we provide a comprehensive overview of their applications across various fields, including environmental remediation, energy storage, and thermoelectric and optoelectronic technologies. We also discuss promising new directions for the use of Magnéli phase titanium suboxides and solutions to challenges in energy and environment-related applications, and provide guidance on how these materials can be developed and utilised to meet diverse research application needs. By making use of control measures to mitigate the potential hazards associated with their nanoparticles, Magnéli phases can be considered as versatile materials with potential for next generation energy needs.

Mesoporous PtIr alloy single-particle: A novel SECM-tip for in situ monitoring NO of single-cell

As a vital factor in cell metabolism, nitric oxide (NO) is associated with nitrosative stress and subsequent inflammations and diseases. In situ, real-time NO monitoring is challenging due to its relative trace concentration and fast diffusion in cell. Scanning electrochemical microscopy (SECM) is suited uniquely for single-cell analysis, and its electrochemical response to targets can be further enhanced by improving the interfacial properties of its tip. Here, an ultramicroelectrodes (UMEs) modification strategy based on bimetallic single-particle was proposed for the first time. This mesoporous platinum/iridium alloy single-particle (mPtIr SP) interface using micelle-assisted electrodeposition was characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). And the nucleation kinetic progress which can be defined as "oil-in-water-like" electrodeposition was discussed in detail. The high sensitivity (203.86 μA/μM·cm2) and good selectivity for NO detection benefits from the high catalysis of the PtIr alloy and the high mass transfer properties of the porous interface. In particular, this novel UME can real-time monitor NO release from a single MCF-7 cell stimulated by perfluorooctanoic acid (PFOA), providing new ideas for contaminant toxicity assessment, health diagnostics, and disease treatment.

Preparation and Electrochemical Applications of Magnéli Phase Titanium Suboxides: A Review

Magnéli phase titanium suboxides (M-TSOs) belong to a type of sub-stoichiometric titanium oxides based on the crystal structure of rutile TiO2. They possess a unique shear structure, granting them exceptional electrical conductivity and corrosion resistance. These two advantages are crucial for electrode materials in electrochemistry, hence the significant interest from numerous researchers. However, the preparation of M-TSOs is uneconomic due to high temperature reduction and other complex synthesis process, thus limiting their practical application in electrochemical fields. This review delves into the crystal structure, properties, and synthesis methods of M-TSOs, and touches on their applications as electrocatalysts in wastewater treatment and electrochemical water splitting. Furthermore, it highlights the research challenges and potential future research directions in M-TSOs.

Sn Bulk Phase Doping and Surface Modification on Ti4 O7 for Oxygen Reduction to Hydrogen Peroxide

Developing stable and highly selective two-electron oxygen reduction reaction (2e- ORR) electrocatalysts for producing hydrogen peroxide (H2 O2 ) is considered a major challenge to replace the anthraquinone process and achieve a sustainable green economy. Here, we doped Sn into Ti4 O7 (D-Sn-Ti4 O7 ) by simple polymerization post-calcination method as a high-efficiency 2e- ORR electrocatalyst. In addition, we also applied plain calcination after the grinding method to load Sn on Ti4 O7 (L-Sn-Ti4 O7 ) as a comparison. However, the performance of L-Sn-Ti4 O7 is far inferior to that of the D-Sn-Ti4 O7 . D-Sn-Ti4 O7 exhibits a starting potential of 0.769 V (versus the reversible hydrogen electrode, RHE) and a high H2 O2 selectivity of 95.7 %. Excitingly, the catalyst can maintain a stable current density of 2.43 mA ⋅ cm-2 for 3600 s in our self-made H-type cell, and the cumulative H2 O2 production reaches 359.2 mg ⋅ L-1 within 50,000 s at 0.3 V. The performance of D-Sn-Ti4 O7 is better than that of the non-noble metal 2e- ORR catalysts reported so far. The doping of Sn not only improves the conductivity but also leads to the lattice distortion of Ti4 O7 , further forming more oxygen vacancies and Ti3+ , which greatly improves its 2e- ORR performance compared with the original Ti4 O7 . In contrast, since the Sn on the surface of L-Sn-Ti4 O7 displays a synergistic effect with Tin+ (3≤n≤4) of Ti4 O7 , the active center Tin+ dissociates the O=O bond, making it more inclined to 4e- ORR.

Boosting Bifunctional Catalysis by Integrating Active Faceted Intermetallic Nanocrystals and Strained Pt-Ir Functional Shells

PtIr-based nanostructures are fascinating materials for application in bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysis. However, the fabrication of PtIr nanocatalysts with clear geometric features and structural configurations, which are crucial for enhancing the bifunctionality, remains challenging. Herein, PtCo@PtIr nanoparticles are precisely designed and fabricated with a quasi-octahedral PtCo nanocrystal as a highly atomically ordered core and an ultrathin PtIr atomic layer as a compressively strained shell. Owing to their geometric and core-shell features, the PtCo@PtIr nanoparticles deliver approximately six and eight times higher mass and specific activities, respectively, as an ORR catalyst than a commercial Pt/C catalyst. The half-wave potential of PtCo@PtIr exhibits a negligible decrease by 9 mV after 10 000 cycles, indicating extraordinary ORR durability because of the ordered arrangement of Pt and Co atoms. When evaluated using the ORR-OER dual reaction upon the introduction of Ir, PtCo@PtIr exhibits a small ORR-OER overpotential gap of 679 mV, demonstrating its great potential as a bifunctional electrocatalyst for fabricating fuel cells. The findings pave the way for designing precise intermetallic core-shell nanocrystals as highly functional catalysts.

A Review: Synthesis and Applications of Titanium Sub-Oxides

Magnéli phase titanium oxides, also called titanium sub-oxides (TinO2n-1, 4 < n < 9), are a series of electrically conducting ceramic materials. The synthesis and applications of these materials have recently attracted tremendous attention because of their applications in a number of existing and emerging areas. Titanium sub-oxides are generally synthesized through the reduction of titanium dioxide using hydrogen, carbon, metals or metal hydrides as reduction agents. More recently, the synthesis of nanostructured titanium sub-oxides has been making progress through optimizing thermal reduction processes or using new titanium-containing precursors. Titanium sub-oxides have attractive properties such as electrical conductivity, corrosion resistance and optical properties. Titanium sub-oxides have played important roles in a number of areas such as conducting materials, fuel cells and organic degradation. Titanium sub-oxides also show promising applications in batteries, solar energy, coatings and electronic and optoelectronic devices. Titanium sub-oxides are expected to become more important materials in the future. In this review, the recent progress in the synthesis methods and applications of titanium sub-oxides in the existing and emerging areas are reviewed.

Supported Iridium-based Oxygen Evolution Reaction Electrocatalysts - Recent Developments

The commercialization of acidic proton exchange membrane water electrolyzers (PEMWE) is heavily hindered by the price and scarcity of oxygen evolution reaction (OER) catalyst, i. e. iridium and its oxides. One of the solutions to enhance the utilization of this precious metal is to use a support to distribute well dispersed Ir nanoparticles. In addition, adequately chosen support can also impact the activity and stability of the catalyst. However, not many materials can sustain the oxidative and acidic conditions of OER in PEMWE. Hereby, we critically and extensively review the different materials proposed as possible supports for OER in acidic media and the effect they have on iridium performances.

Anchoring Highly Dispersed Pt Electrocatalysts on TiOx with Strong Metal-Support Interactions via an Oxygen Vacancy-Assisted Strategy as Durable Catalysts for the Oxygen Reduction Reaction

Pt electrocatalysts with high activity and durability have still crucial issues for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). In this study, a novel catalyst consisting of Pt nanoparticles (NPs) on TiO_x/C composites (TiO_x-V_o-H/C) with abundant oxygen vacancies (V_o) is proposed, which is abbreviated as PTO-V_o-H/C. The introduction of V_o helps anchor highly dispersed Pt NPs with low loading and strengthen the strong metal-support interaction (SMSI), which benefits to the enhanced ORR catalytic activity. Moreover, the accelerated durability test (ADT) demonstrates the higher retention of ORR activity for PTO-V_o-H/C. Experimental and theoretical analyses reveal that electronic interactions between Pt NPs and TiO_x/C composite support give rise to an electron-rich Pt NPs and strong SMSI effect, which is favorable for the electron transfer and stabilization of Pt NPs. More importantly, the assembled PEMFC with PTO-V_o-H/C shows only 6.9% of decay on maximum power density after 3000 ADT cycles while the performance of Pt/C sharply decreased. This work provides a new insight into the unique vacancy regulation of dispersive Pt on metal oxides for superior ORR performance.

Semiconducting Polymers for Oxygen Evolution Reaction under Light Illumination

Sunlight-driven water splitting to produce hydrogen fuel has stimulated intensive scientific interest, as this technology has the potential to revolutionize fossil fuel-based energy systems in modern society. The oxygen evolution reaction (OER) determines the performance of overall water splitting owing to its sluggish kinetics with multielectron transfer processing. Polymeric photocatalysts have recently been developed for the OER, and substantial progress has been realized in this emerging research field. In this Review, the focus is on the photocatalytic technologies and materials of polymeric photocatalysts for the OER. Two practical systems, namely, particle suspension systems and film-based photoelectrochemical systems, form two main sections. The concept is reviewed in terms of thermodynamics and kinetics, and polymeric photocatalysts are discussed based on three key characteristics, namely, light absorption, charge separation and transfer, and surface oxidation reactions. A satisfactory OER performance by polymeric photocatalysts will eventually offer a platform to achieve overall water splitting and other advanced applications in a cost-effective, sustainable, and renewable manner using solar energy.

High-performance AEM unitized regenerative fuel cell using Pt-pyrochlore as bifunctional oxygen electrocatalyst

The performance of fixed-gas unitized regenerative fuel cells (FG-URFCs) are limited by the bifunctional activity of the oxygen electrocatalyst. It is essential to have a good bifunctional oxygen electrocatalyst which can exhibit high activity for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). In this regard, Pt-Pb₂Ru₂O_7-x is synthesized by depositing Pt on Pb₂Ru₂O_7-x wherein Pt individually exhibits high ORR while Pb₂Ru₂O_7-x shows high OER and moderate ORR activity. Pt-Pb₂Ru₂O_7-x exhibits higher OER (η_@10mAcm-2 = 0.25 ± 0.01 V) and ORR (η_@-3mAcm-2 = -0.31 ± 0.02 V) activity in comparison to benchmark OER (IrO₂, η_@10mAcm-2 = 0.35 ± 0.02 V) and ORR (Pt/C, η_@-3mAcm-2 = -0.33 ± 0.02 V) electrocatalysts, respectively. Pt-Pb₂Ru₂O_7-x shows a lower bifunctionality index (η_{@10mAcm-2, OER} ^- η_{@-3mAcm-2, ORR}) of 0.56 V with more symmetric OER-ORR activity profile than both Pt (>1.0 V) and Pb₂Ru₂O_7-x (0.69 V) making it more useful for the AEM (anion exchange membrane) URFC or metal-air battery applications. FG-URFC tested with Pt-Pb₂Ru₂O_7-x and Pt/C as bifunctional oxygen electrocatalyst and bifunctional hydrogen electrocatalyst, respectively, yields a mass-specific current density of 715 ± 11 A/g_cat ^-1 at 1.8 V and 56 ± 2 A/g_cat ^-1 at 0.9 V under electrolyzer mode and fuel-cell mode, respectively. The FG-URFC shows a round-trip efficiency of 75% at 0.1 A/cm^-2, underlying improvement in AEM FG-URFC electrocatalyst design.

Magneli-Phase Titanium Suboxide Nanocrystals as Highly Active Catalysts for Selective Acetalization of Furfural

Alongside TiO₂, Magneli-phase titanium suboxide having the composition of Ti_nO_2n-1 is a kind of attractive functional materials composed of titanium. However, there still remain problems to be overcome in the synthesis of titanium suboxide; the existing synthesis methods require high temperature typically over 1000 °C and/or postsynthesis purification. This study presents a novel approach to synthesis of titanium suboxide nanoparticles through solid-phase reaction of TiO₂ with TiH₂. Crystal phases of titanium suboxide were easily controlled by changing TiO₂/TiH₂ molar ratios in a TiO₂-TiH₂ mixed precursor, and a series of titanium suboxide nanoparticles including Ti₂O₃, Ti₃O₅, Ti₄O₇, and Ti₈O₁₅ were successfully obtained. The reaction of TiO₂ with TiH₂ proceeded at a relatively low temperature due to the high reactivity of TiH₂, giving titanium suboxide nanoparticles without any postsynthesis purification. Ti₂O₃ nanoparticles and TiO₂ were applied as solid acid catalysts for reaction of furfural with 2-propanol. Ti₂O₃ showed a high catalytic activity and high selectivity for acetalization of furfural, while TiO₂ showed only poor activity for transfer hydrogenation of furfural. The difference in catalytic properties is discussed in terms of the acid properties of Ti₂O₃ and TiO₂.

Size Control of Ti4O7 Nanoparticles by Carbothermal Reduction Using a Multimode Microwave Furnace

Utilization of Ti4O7 in applications such as catalyst support calls for control over the size of the Ti4O7 nanoparticles. This can be achieved using a simple process such as carbothermal reduction. In this study, various sizes of Ti4O7 nanoparticles (25, 60, and 125 nm) were synthesized by carbothermal reduction using a multimode microwave apparatus. It was possible to produce Ti4O7 nanoparticles as small as 25 nm by precisely controlling the temperature, heating process, and holding time of the sample while taking advantage of the characteristics of microwave heating such as rapid and volumetric heating. The results show that microwave carbothermal reduction is advantageous in controlling the size of the Ti4O7 nanoparticles.