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Electrodeposited amorphous hydrated iridium oxide (IrOx) is a promising material for pH sensing due to its high sensitivity and the ease of fabrication. However, durability and variability continue to restrict the sensors effectiveness. Variation in probe films can be seen in both performance and fabrication, but it has been found that performance variation can be controlled with potentiostatic conditioning (PC). To make proper use of this technique, the morphological and chemical changes affecting the conditioning process must be understood. Here, a thorough study of this material, after undergoing PC in a pH-sensing-relevant potential regime, was conducted by voltammetry, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Fitting of XPS data was performed, guided by raw trends in survey scans, core orbitals, and valence spectra, both XPS and UPS. The findings indicate that the PC process can repeatably control and conform performance and surface bonding to desired calibrations and distributions, respectively; PC was able to reduce sensitivity and offset ranges to as low as ±0.7 mV/pH and ±0.008 V, respectively, and repeat bonding distributions over ~2 months of sample preparation. Both Ir/O atomic ratios (shifting from 4:1 to over 4.5:1) and fitted components assigned hydroxide or oxide states based on the literature (low-voltage spectra being almost entirely with suggested hydroxide components, and high-voltage spectra almost entirely with suggested oxide components) trend across the polarization range. Self-consistent valence, core orbital, and survey quantitative trends point to a likely mechanism of ligand conversion from hydroxide to oxide, suggesting that the conditioning process enforces specific state mixtures that include both theoretical Ir(III) and Ir(IV) species, and raising the conditioning potential alters the surface species from an assumed mixture of Ir species to more oxidized Ir species.

The degradation behaviors of three iridium-based oxides, SrIrO 3 , Sr 2 IrO 4 , and Sr 4 IrO 6 , in sulfuric acid solution for OER operation are investigated. It's discovered that the connection configurations of [IrO 6 ] octahedra units in the crystalline structure impact on the catalyst stability, in terms of the kinetics of cation dissolution, surface amorphization, bulk structure transformation, and etc. [Display omitted] • The degradation behaviors of three iridium oxides, SrIrO 3 , Sr 2 IrO 4 , and Sr 4 IrO 6 , are found to be strongly affected by the crystalline structure, particularly the inter-connection configurations of [IrO 6 ] octahedra units. • Sr2+ leaching leads to precipitation of non-conductive SrSO 4 on catalyst surface, which gradually blocks the reactive Ir sites. • The rapid formation of an amorphous IrO x surface layer can offer advantages in terms of electrochemical stability, preventing continuous leaching of Sr and Ir from the bulk structure. Large-scale hydrogen production by electrocatalytic water splitting still remains as a critical challenge due to the severe catalyst degradation during the oxygen evolution reaction (OER) in acidic media. In this study, we investigate the structural impacts on catalyst degradation behaviors using three iridium-based oxides, namely SrIrO 3 , Sr 2 IrO 4 , and Sr 4 IrO 6 as model catalysts. These Ir oxides possess different connection configurations of [IrO 6 ] octahedra units in their structure. Stable OER performance is observed on SrIrO 3 and attributed to the edge-linked [IrO 6 ] structure and rapid formation of a continuous IrO x layer on its surface, which functions not only as the "real" catalyst but also a shield preventing continuous cation leaching (with <1.0 at.% of Ir leaching). In comparison, both Sr 2 IrO 4 and Sr 4 IrO 6 catalysts demonstrate quick current fading with structure transformation to rutile IrO 2 and formation of inconducive SrSO 4 precipitates on surface, blocking the reactive sites. Nevertheless, over 60 at.% of Ir leaching is detected from the Sr 4 IrO 6 catalyst due to its isolated [IrO 6 ] structure configuration. Results of this work highlight the structural impacts on the catalyst stability in acidic OER conditions. [ABSTRACT FROM AUTHOR]

The quality of in situ XAS of electrochemical systems is highly sensitive to electrode disturbances, such as gas evolution and gas consumption at an electrolyte/catalyst interface. A novel in situ spectro‐electrochemical X‐ray absorption spectroscopy (SPEC‐XAS) cell is presented as a new tool for the characterisation of gas evolving and consuming electrocatalysts at high overpotentials. By utilising a thin, porous membrane with efficient electrolyte and gas circulating loops, an improved three phase interface is established that enabled efficient gas supply and minimised the interference from bubble formation. X‐ray absorption spectroscopy (XAS) measurements were conducted in fluorescence mode with three experiments selected to demonstrate the cell's performance. The first two reactions; an in‐situ study of a highly active amorphous iridium oxide catalyst during the oxygen evolution reaction (OER) and an in‐situ study of copper oxide during the carbon dioxide reduction reaction (CO2RR) are used to exemplify the XAS data quality achieved under operational conditions. Thirdly, a detailed XAS investigation of a highly dispersed platinum catalyst during the oxygen reduction reaction (ORR) is presented, along with comparative data in nitrogen. These measurements show the retention of oxygen on the surface of the platinum metal particles down to 0.48 V (vs. RHE), well below the platinum oxide reduction peak. [ABSTRACT FROM AUTHOR]

New materials for oxygen evolution reaction (OER) electrocatalysts in alkaline conditions have been highly investigated in recent years for the advancement of water splitting. However, questions such as the lack of stability and the use of noble metals as electrocatalysts still need to be addressed. In this study, we report the synthesis and electrocatalytic properties of a series of wolframite tungsten‐based materials (MWO4, M=Fe, Mn, Ni, Co) towards OER in basic conditions. Our results showed that Ni0.5Mn0.5WO4 is a promising electrocatalyst, exhibiting ease of preparation, stability over the course of our experiments, and OER activity comparable to the standard iridium oxide. This study highlights the potential of wolframite tungsten‐based materials as a new class of electrocatalysts for OER in alkaline conditions. [ABSTRACT FROM AUTHOR]

Technically viable electrocatalysts for the oxygen evolution reaction (OER) must be both active and stable under the harsh conditions at an electrolyser anode. While numerous highly active metal‐oxide catalysts have been identified, only very few are sufficiently stable, with iridium oxides being the most prominent. In this perspective, we draw insights from OER mechanisms to circumvent the activity‐stability conundrum generally plaguing the development of OER catalysts. In the commonly considered OER mechanisms, one or several metal‐oxygen (M−O) bonds are required to be broken along the OER pathway, providing a mechanistic link between the OER and oxide decomposition. However, a recently discovered mechanism on crystalline iridium dioxide provides a new OER pathway without M−O bond breakages, thus enabling the combination of sufficient activity and stability. [ABSTRACT FROM AUTHOR]

Dimensionally stable anodes (DSAs) offer great advantages as insoluble anodes for electrolytic copper foils. Titanium-based iridium dioxide electrode has low oxygen evolution potential, which can reduce energy consumption in industrial production. In view of the excellent oxygen evolution performance of MoS2 in alkaline environment, molybdenum disulfide is considered to be loaded on Ti/IrO2 electrode by electrodeposition to improve the oxygen evolution efficiency of electrolytic copper foil anode in copper sulfate. The structure of the composite anode was characterized using surface analysis techniques such as XRD and SEM. The results manifested that the surface of the anode was shallower and had fewer pits, which effectively improved the microscopic morphology of the Ti/IrO2/MoS2. The oxygen evolution potential of Ti/IrO2/MoS2 composite anode determined by oxygen evolution polarization curve (LSV) was 1.25 V, which was lower than that of commercially available Ti/IrO2-Ta2O5 anodes and had the largest oxygen evolution active surface area. In addition, the experiment with the electrolytic copper foil using the Ti/IrO2/MoS2 anode revealed that the surface flatness of the copper foil was high and the average grain size was 32 nm, which further confirmed that the application of the Ti/IrO2/MoS2 anode in the electrolytic copper foil area can lessen the slot voltage and save cost. [ABSTRACT FROM AUTHOR]

Electrochemical water splitting, a sustainable method for hydrogen production, faces the challenge of slow oxygen evolution reaction (OER) kinetics. Iridium oxide (IrO2) is widely regarded as the most effective catalyst for OER due to its excellent properties. Compared to nanoparticles, IrO2 thin films exhibit significant advantages in OER, including a uniform and stable catalytic interface and excellent mechanical strength. This paper reviews recent advancements in one-step deposition techniques for the preparation of IrO2 thin films and their application in OER. Additionally, it analyzes the advantages and disadvantages of various methods and the latest research achievements, and briefly outlines the future trends and applications. [ABSTRACT FROM AUTHOR]

Oxygen evolution reaction (OER) plays a crucial role in developing energy conversion and adjusting electronic structure of the electrocatalysts can effectively improve the catalytic activity and stability. However, it is a challenge to adjust the electronic structure on two-dimensional iridium dioxide nanosheets (IrO2 NS), which have the advantages of high atom utilization. Here, we regulate the surface properties of IrO2 NS through sulfonated carbon dots (SCDs) to promote the OER catalytic process. The catalyst IrO2 NS/SCDs-2 exhibited excellent catalytic activity with a lower overpotential of 180 mV than IrO2 NS (230 mV) at the current density of 10 mA·cm−2 in a 0.5 M H2SO4 solution. And after 160 h of stability testing, the overpotential of IrO2 NS/SCDs-2 only decreased by 4 mV. Moreover, transient potential scanning test can visually demonstrate that the addition of SCDs improves the conductivity of the catalyst and increases the electron transfer rate. [ABSTRACT FROM AUTHOR]

Infected wounds pose a significant clinical challenge due to bacterial resistance, recurrent infections, and impaired healing. Reactive oxygen species (ROS)-based strategies have shown promise in eradicating bacterial infections. However, the excess ROS in the infection site after treatments may cause irreversible damage to healthy tissues. To address this issue, we developed bovine serum albumin-iridium oxide nanoclusters (BSA-IrOx NCs) which enable photo-regulated ROS generation and scavenging using near infrared (NIR) laser. Upon NIR laser irradiation, BSA-IrOx NCs exhibit enhanced photodynamic therapy, destroying biofilms and killing bacteria. When the NIR laser is off, the nanoclusters' antioxidant enzyme-like activities prevent inflammation and repair damaged tissue through ROS clearance. Transcriptomic and metabolomic analyses revealed that BSA-IrOx NCs inhibit bacterial nitric oxide synthase, blocking bacterial growth and biofilm formation. Furthermore, the nanoclusters repair impaired skin by strengthening cell junctions and reducing mitochondrial damage in a fibroblast model. In vivo studies using rat infected wound models confirmed the efficacy of BSA-IrOx NCs. This study presents a promising strategy for treating biofilm-induced infected wounds by regulating the ROS microenvironment, addressing the challenges associated with current ROS-based antibacterial approaches.

Efficient water‐splitting is severely limited by the anodic oxygen evolution reaction (OER). Iridium oxides remain one of the only viable catalysts under acidic conditions due to their corrosion resistance. We have previously shown that heat‐treating high‐activity amorphous iridium oxyhydroxide in the presence of residual lithium carbonate leads to the formation of lithium‐layered iridium oxide, suppressing the formation of low‐activity crystalline rutile IrO2. We now report the synthesis of Na‐IrOx and K‐IrOx featuring similarly layered crystalline structures. Electrocatalytic tests confirm Li‐IrOx retains similar electrocatalytic activity to commercial amorphous IrO2 ⋅ 2H2O and with increasing size of the intercalated cation, the activity towards the OER decreases. However, the synthesised electrocatalysts that contain layers show greater stability than crystalline rutile IrO2 and amorphous IrO2 ⋅ 2H2O, suggesting these compounds could be viable alternatives for industrial PEM electrolysers where durability is a key performance measure. [ABSTRACT FROM AUTHOR]

The widespread application of green hydrogen production technologies requires cost reduction of crucial elements. To achieve this, a viable pathway to reduce the iridium loading in proton exchange membrane water electrolysis (PEMWE) is explored. Herein, a scalable synthesis method based on a photodeposition process for a TiO2@IrOx core–shell catalyst with a reduced iridium content as low as 40 wt.% is presented. Using this synthesis method, titania support particles homogeneously coated with a thin iridium oxide shell of only 2.1 ± 0.4 nm are obtained. The catalyst exhibits not only high ex situ activity, but also decent stability compared to commercially available catalysts. Furthermore, the unique core–shell structure provides a threefold increased electrical powder conductivity compared to structures without the shell. In addition, the low iridium content facilitates the fabrication of sufficiently thick catalyst layers at decreased iridium loadings mitigating the impact of crack formation in the catalyst layer during PEMWE operation. It is demonstrated that the novel TiO2@IrOx core–shell catalyst clearly outperforms the commercial reference in single‐cell tests with an iridium loading below 0.3 mgIr cm−2 exhibiting a superior iridium‐specific power density of 17.9 kW gIr−1 compared to 10.4 kW gIr−1 for the commercial reference. [ABSTRACT FROM AUTHOR]

Active and stable electrocatalysts with low precious metal loading is essential for the widespread application of proton-exchange water electrolyzers. Construction of core-shell structure offers the possibility to achieve high catalytic activity and good stability, and simultaneously to reduce the precious-metal loading. Here, Co 3 O 4 -core IrO x -shell nanoparticles (Co 3 O 4 @IrO x) are synthesized by immersing the solvothermal synthesized Co 3 O 4 in alkaline IrCl 3 aqueous solution, followed by annealing at 350 °C for 2 h. The Co 3 O 4 @IrO x -10, which exhibits the highest oxygen evolution reaction (OER) activity when supported on carbon paper, are 9.76 nm in average diameter, and the surface IrO x layer is about 0.97 nm. Only 337 mV overpotentials are required to reach the 10 mA cm−2 OER current densities in 0.1 M HClO 4 for the Co 3 O 4 @IrO x -10, with the mass activity reaches 1.44 A mg−1 Ir at 370 mV overpotentials. The high OER activity is originated from the increased number of active sites and more facile kinetics, demonstrated by the lower charge transfer resistance, lower activation energy and lower Tafel slope values. The optimized adsorption energy of OH* intermediates caused by the electronic interaction between the Co 3 O 4 core and the IrO x shell facilitates the OER kinetics. The Co 3 O 4 @IrO x -10 supported on carbon paper is stable towards the long-term OER in acid, and the IrO x shell layer can effectively protect the Co 3 O 4 core. The Co 3 O 4 @IrO x -10 are promising candidates as the low precious metal electrocatalysts for OER in acid. • The Co 3 O 4 @IrO x -y core-shell nanoparticles are synthesized successfully. • The core-shell structure enhanced the activity and stability of the catalyst. • The core-shell structure significantly reduced the amount of IrO x addition. • The electron interaction between Co 3 O 4 and IrO x optimizes the adsorption energy of OH* intermediates. [ABSTRACT FROM AUTHOR]

Developing highly active and stable electrocatalysts is essential for the large‐scale production of hydrogen from alkaline water. In this work, Ag single atoms and nanoparticles co‐decorated Co hydro(oxy)oxide (Ag SAs&NPs@CoO(O)H) is synthesized by a facile one‐step approach. Notably, the overpotential of Ag SAs&NPs@CoO(O)H is 200 mV at current density of 50 mA cm−2 during oxygen evolution reaction (OER). Meanwhile, it can display the mass activity of 637.47 A g−1Ag under 300 mV, which is 212.49 times higher than that of commercial IrO2. Moreover, the assembled Pt/C // Ag SAs&NPs@CoO(O)H system only requires 1.9 V to reach an industrial current density of 1000 mA cm−2 in alkaline water electrolyzer and exhibits excellent stability at large current density of 1000 mA cm−2. Furthermore, in situ Raman spectroscopy analysis coupled with theoretical calculations reveals an novel active site switching mechanism is found on Ag SAs&NPs@CoO(O)H. Specifically, the O* preferentially generates on the Ag NPs and then switches toward the Co3+ site in CoO(O)H to produce OOH* and O2. Meanwhile, the Ag SAs in the lattice of CoO(O)H can exert an inhibitory force on the reconstruction process of CoOOH to Co(OH)2, resulting in excellent anti‐dissolution stability. [ABSTRACT FROM AUTHOR]

pH regulation in human biofluids is a crucial step for disease diagnosis and health monitoring. Traditional pH sensors are limited by their bulky size in wearable systems, and fragile glass tips require frequent calibration, thus limiting their use in continuous monitoring. Flexible sensors, particularly those utilizing microwires and thread-based substrates, present advantages for small sample analysis, including natural breathability and suitability for bandage or textile integration. This study examines iridium oxide and silver–silver chloride coated on thin gold wires, fabricated using sol–gel and dip-coating processes known for their simplicity. The flexible microwires demonstrated promising pH performance from a study of their pH characteristics, sensitivity, hysteresis, and potential drift. Electrodes tested in microwells allowed for small sample volumes and localized pH measurement in a controlled environment. Additional integration into fabrics for sweat sensing in wearables highlighted their potential for continuous, real-time health monitoring applications. [ABSTRACT FROM AUTHOR]

Ti/IrO2-Ta2O5 electrodes are extensively utilized in the electrochemical industries such as copper foil production, cathodic protection, and wastewater treatment. However, their performance degrades rapidly under high current densities and severe oxygen evolution conditions. To address this issue, we have developed a composite anode of Ti/Ta-Ti/IrO2-Ta2O5 with a Ta-Ti alloy interlayer deposited on a Ti substrate by double-glow plasma surface alloying, and the IrO2-Ta2O5 surface coating prepared by the traditional thermal decomposition method. This investigation indicates that the electrode with Ta-Ti alloy interlayer reduces the agglomerates of precipitated IrO2 nanoparticles and refines the grain size of IrO2, thereby increasing the number of active sites and enhancing the electrocatalytic activity. Accelerated lifetime tests demonstrate that the Ti/Ta-Ti/IrO2-Ta2O5 electrode exhibits a much higher stability than the Ti/IrO2-Ta2O5 electrode. The significant improvement in electrochemical stability is attributed to the Ta-Ti interlayer, which offers high corrosion resistance and effective protection for the titanium substrate. [ABSTRACT FROM AUTHOR]

To evaluate the properties of an Ir‐based catalyst (IrOx), which is the anode in polymer electrolyte membrane‐type water electrolysis, a new method for estimating the electrochemical surface area (ECSA) is required. ECSA evaluation using the underpotential deposition of mercury (Hg‐UPD) can be applied to metals and oxides. However, research regarding Hg‐UPD is needed because several Hg(II)/Hg(I) redox reactions occur simultaneously, and direct evidence of Hg‐UPD on IrOx has not been reported. We previously confirmed the Hg‐UPD phenomenon on Ir polycrystalline films using the electrochemical quartz crystal microbalance (EQCM) method. However, measurements on IrOx electrodes were not performed. In this study, Ir and IrOx electrodes are prepared by the sputtering method, and their Hg deposition behavior observed by EQCM. We quantitatively confirm Hg‐UPD on Ir metal surfaces and provide new evidence of Hg‐UPD on the IrOx surface. These results contribute to establishing the ECSA evaluation of various Ir‐based catalysts. [ABSTRACT FROM AUTHOR]

Ongoing research to develop advanced electrocatalysts for the oxygen evolution reaction (OER) is needed to address demand for efficient energy conversion and carbon‐free energy sources. In the OER process, acidic electrolytes have higher proton concentration and faster response than alkaline ones, but their harsh strongly acidic environment requires catalysts with greater corrosion and oxidation resistance. At present, iridium oxide (IrO2) with its strong stability and excellent catalytic performance is the catalyst of choice for the anode side of commercial PEM electrolysis cells. However, the scarcity and high cost of iridium (Ir) and the unsatisfactory activity of IrO2 hinder industrial scale application and the sustainable development of acidic OER catalytic technology. This highlights the importance of further research on acidic Ir‐based OER catalysts. In this review, recent advances in Ir‐based acidic OER electrocatalysts are summarized, including fundamental understanding of the acidic OER mechanism, recent insights into the stability of acidic OER catalysts, highly efficient Ir‐based electrocatalysts, and common strategies for optimizing Ir‐based catalysts. The future challenges and prospects of developing highly effective Ir‐based catalysts are also discussed. [ABSTRACT FROM AUTHOR]

Proton exchange membrane water electrolysis (PEMWE) is considered a promising technology for coupling with renewable energy sources to achieve clean hydrogen production. However, constrained by the sluggish kinetics of the anodic oxygen evolution reaction (OER) and the acidic abominable environment render the grand challenges in developing the active and stable OER electrocatalyst, leading to low efficiency of PEMWE. Herein, we develop the rutile‐type IrO2 nanoparticles with abundant grain boundaries and the continuous nanostructure through the joule heating and sacrificial template method. The optimal candidate (350‐IrO2) demonstrates remarkable electrocatalytic activity and stability during the OER, presenting a promising advancement for efficient PEMWE. DFT calculations verified that grain boundaries can modulate the electronic structure of Ir sites and optimize the adsorption of oxygen intermediates, resulting in the accelerated kinetics. 350‐IrO2 affords a rapid OER process with 20 times higher mass activity (0.61 A mgIr−1) than the commercial IrO2 at 1.50 V vs. RHE. Benefiting from the reduced overpotential and the preservation of the stable rutile structure, 350‐IrO2 exhibits the stability of 200 h test at 10 mA cm−2 with only trace decay of 11.8 mV. Moreover, the assembled PEMWE with anode 350‐IrO2 catalyst outputs the current density up to 2 A cm−2 with only 1.84 V applied voltage, long‐term operation for 100 h without obvious performance degradation at 1 A cm−2. [ABSTRACT FROM AUTHOR]

Metal exsolution engineering has been regarded as a promising strategy for activating intrinsically inert perovskite oxide catalysts toward efficient oxygen evolution reaction. Traditional metal exsolution processes on perovskites are often achieved by using the reducing hydrogen gas; however, this is not effective for the relatively stable phase, such as Ruddlesden–Popper perovskite oxides. To address this issue, triphenylphosphine is proposed to be a reduction promotor for accelerating the reduction and migration of the target metal atoms, aiming to achieve the effective exsolution of metallic species from Ruddlesden–Popper‐type parent perovskites. Upon oxygen evolution reaction, these exsolved metallic aggregates are reconstructed into oxyhydroxides as the real active centers. After further modification by low‐percentage iridium oxide nanoclusters, the optimal catalyst delivered an overpotential as low as 305 mV for generating the density of 10 mA cm−2, outperforming these reported noble metal‐containing perovskite‐based alkaline oxygen evolution reaction electrocatalysts. This work provides a potential approach to activate catalytically inert oxides through promoting surface metal exsolution and explores a novel class of Ruddlesden–Popper‐type oxides for electrocatalytic applications. [ABSTRACT FROM AUTHOR]

Ir-based electrocatalysts are commonly acknowledged as top-performing materials for water oxidation under acidic conditions. Decreasing the precious metal loading and improving the intrinsic activity of Ir sites are vital for creating effective electrocatalysts for PEMWE applications. Here, we employed a simple solvothermal method to create IrO x @TiO 2 core-shell structure electrocatalyst for efficient anodic OER in acidic environment. The obtained IrO x @TiO 2 requires an overpotential of only 227 mV to achieve 10 mA cm−2 and maintains such stability over 200 h. Furthermore the intrinsic and mass activity of IrO x @TiO 2 demonstrate a remarkable improvement of hundreds of times compared to that of IrO 2. The core-shell structure of IrO x @TiO 2 possesses a high specific surface area, with the amorphous IrO x shell layer enhancing the catalytic activity of the Ir sites. Further structural analysis of the post-OER IrO x @TiO 2 revealed that the amorphous IrO x was effectively stabilized and high-valent IrO x generated on its surface may be more favorable for acidic water oxidation process. This study introduces a practical approach for developing high-performance, low-iridium-loading acidic OER electrocatalysts. IrO x @TiO 2 with a core-shell structure exhibits outstanding acidic activity and stability accompanied by excellent mass activity and TOF value, and its simple synthesis strategy is informative for the synthesis of Ir-based catalysts. [Display omitted] • IrO x @TiO 2 realizes η 10 at 227 mV and OER stability within 200 h in 0.5 M H 2 SO 4. • IrO x @TiO 2 improves precious metal utilization while ensuring a certain intrinsic activity. • IrO x @TiO 2 maintains excellent structural stability and efficient catalysis at low Ir loadings. [ABSTRACT FROM AUTHOR]

It is found that mixed-valence iridium oxides electrodeposited on the surface of a glassy carbon electrode exhibit catalytic activity in the oxidation of caffeine. In this case, a more pronounced catalytic effect is obtained on an electrode modified with a composite based on a film of a perfluorinated sulfopolymer (Nafion) and mixed-valence iridium oxides. A selective voltammetric method for the determination of caffeine is developed. A linear logarithmic dependence of current on the caffeine concentration is observed in the range from 1 × 10–8 to 5 × 10–3 M. The developed method was used to determine caffeine in energy drinks. [ABSTRACT FROM AUTHOR]

Highlights: Electrodeposited amorphous IrOx thin electrodes are first developed for proton exchange membrane electrolyzer cells. An ultralow loading of 0.075 mg cm−2 archives superior performance to catalyst-coated membrane (2 mg cm−2). > 96% of catalyst savings and > 42-fold higher catalyst utilization are demonstrated. Herein, ionomer-free amorphous iridium oxide (IrOx) thin electrodes are first developed as highly active anodes for proton exchange membrane electrolyzer cells (PEMECs) via low-cost, environmentally friendly, and easily scalable electrodeposition at room temperature. Combined with a Nafion 117 membrane, the IrOx-integrated electrode with an ultralow loading of 0.075 mg cm−2 delivers a high cell efficiency of about 90%, achieving more than 96% catalyst savings and 42-fold higher catalyst utilization compared to commercial catalyst-coated membrane (2 mg cm−2). Additionally, the IrOx electrode demonstrates superior performance, higher catalyst utilization and significantly simplified fabrication with easy scalability compared with the most previously reported anodes. Notably, the remarkable performance could be mainly due to the amorphous phase property, sufficient Ir3+ content, and rich surface hydroxide groups in catalysts. Overall, due to the high activity, high cell efficiency, an economical, greatly simplified and easily scalable fabrication process, and ultrahigh material utilization, the IrOx electrode shows great potential to be applied in industry and accelerates the commercialization of PEMECs and renewable energy evolution. [ABSTRACT FROM AUTHOR]

A special membrane electrode assembly to measure operando X‐ray absorption spectra and resonant photoemission spectra of mesoporous templated iridium oxide films is used. These films are calcined to different temperatures to mediate the catalyst activity. By combining operando resonant photoemission measurements of different films with ab initio simulations these are able to unambiguously distinguish µ2‐O (bridging oxygen) and µ1‐O (terminal oxygen) in the near‐surface regions of the catalysts. The intrinsic activity of iridium oxide scales with the formation of µ1‐O (terminal oxygen) is found. Importantly, it is shown that the peroxo species do not accumulate under reaction conditions. Rather, the formation of µ1‐O species, which are active in O−O bond formation during the OER, is the most oxidized oxygen species observed, which is consistent with an O−O rate‐limiting step. Thus, the oxygen species taking part in the electrochemical oxidation of water on iridium electrodes are more involved and complex than previously stated. This result highlights the importance of employing theory together with true and complementary operando measurements capable of probing different aspects of catalysts surfaces during operation. [ABSTRACT FROM AUTHOR]

Hexavalent iridium (IrVI) oxide is predicted to be more active and stable than any other iridium oxide for the oxygen evolution reaction in acid; however, its experimental realization remains challenging. In this work, we report the synthesis, characterization, and application of atomically dispersed IrVI oxide (IrVI-ado) for proton exchange membrane (PEM) water electrolysis. The IrVI-ado was synthesized by oxidatively substituting the ligands of potassium hexachloroiridate(IV) (K2IrCl6) with manganese oxide (MnO2). The mass-specific activity (1.7 × 105 amperes per gram of iridium) and turnover number (1.5 × 108) exceeded those of benchmark iridium oxides, and in situ x-ray analysis during PEM operations manifested the durability of IrVI at current densities up to 2.3 amperes per square centimeter. The high activity and stability of IrVI-ado showcase its promise as an anode material for PEM electrolysis. [ABSTRACT FROM AUTHOR]

The design of diatomic catalysts with uniformly dispersed metal atoms is expected to improve catalytic performance, which is conducive to the intensive comprehending of the synergistic mechanism between dual-metal sites for the oxygen evolution reaction (OER) at the atomic level. Herein, we design a strategy to immobilize bimetallic Fe-Co atoms onto nitrogen-doped graphene to obtain a diatomic catalyst (DA-FC-NG) with FeN3-CoN3 configuration. The DA-FC-NG shows excellent OER activity with a low overpotential (η10 = 268 mV), which is superior to commercial iridium dioxide catalysts. Theoretical calculations uncover that the excellent activity of DA-FC-NG is due to the interaction between Fe and Co diatoms, which causes charge rearrangement and induces the adsorption of intermediates on the Fe–O–Co bridge structure, thus improving the catalytic OER performance. This work is of great significance for the design of highly active diatomic catalysts to replace noble metal catalysts for energy-related applications. [ABSTRACT FROM AUTHOR]

Catalytically driven electrochemical hydrogen evolution reaction (HER) holds immense promise for meeting renewable energy demands. In this study, we have reported highly efficient HER catalyst utilizing a novel electrode composed of titanium (Ti) sheet with gold and iridium oxide (Ti/Au-IrO x), compared to a conventional Pt electrode. The fabrication process involved anodizing a Ti strip to form a TiO 2 film, onto which Au and IrO x particles were sequentially deposited, followed by cathodic and anodic reactions, respectively. The resulting Ti/TiO 2 /Au-IrO x electrode exhibited remarkable efficiency in electrochemical HER, significantly reducing the overpotential. Notably, the catalytic onset potential was recorded at −0.10 V, markedly lower than those observed for Ti, Au, and Au-IrO x electrodes individually. This improvement can be attributed to an increase in the catalytic surface area along with a synergistic effect between the TiO 2 metal sheet and the electronic state of Au, which facilitates the adsorption of hydrogen molecules onto the catalytic surface. Furthermore , the presence of IrO x supports the redox counter-reaction, enhancing overall electrochemical conversion kinetics. Electrokinetic parameters such as turnover frequency (TOF), Tafel slope, and exchange current density (j k) were calculated as 0.334 s−1, 64 mV dec−1, and 0.12 mA cm−2, respectively, outperforming other experimental electrodes in this study and approaching values comparable to those of the Pt electrode (0.354 s−1, 36 mV dec−1, and 1.13 mA cm−2, respectively). Additionally, the Ti/TiO 2 /Au-IrO x electrode exhibited lower resistance for charge transfer (Rct) during HER (0.072 kΩ) compared to other electrodes evaluated. These findings underscore the Ti/TiO 2 /Au-IrO x electrode's potential as a highly efficient catalyst for HER under acidic conditions, offering insights into the intricate mechanisms driving catalytic enhancements beyond mere surface area augmentation. • Ti/TiO2/Au-IrOx electrode is an excellent HER catalyst in an acidic medium. • The Volmer-Heyrovsky step is the rate-determining step with 64 mVdec−1 Tafel slope. • Turnover frequency is 0.334 s−1 which is very close to Pt (0.354 s−1). • The catalytic onset potential recorded at −0.10 V with 1 mA cm−2 current density. [ABSTRACT FROM AUTHOR]

Multi-functionalised nano-platforms based on persistent-luminescence nanoparticles (PLNPs) have attracted considerable attention for biomedical applications owing to their lack of background noise and suitability for in vivo imaging without the need for in situ excitation. However, nano-platforms based on PLNPs for continuous photodynamic therapy (PDT) are currently lacking. Herein, we report a nano-platform (LiGa4.99O8:Cr0.01/IrO2, LGO:Cr/IrO2) prepared using PLNPs (LiGa4.99O8:Cr0.01, LGO:Cr) covalently bonded with iridium oxide nanoparticles (IrO2 NPs), producing near-infrared (NIR) persistent luminescence, "afterglow" PDT and photo-thermal therapy (PTT) effects. The LGO:Cr/IrO2 not only exhibits NIR-persistent luminescence at 719 nm and a PTT effect under 808 nm irradiation but also a continuous "afterglow" PDT effect without the need for in situ excitation owing to persistent energy transfer from LGO:Cr to the IrO2 NPs, in turn generating reactive oxygen species (ROS). This multi-functional nano-platform is expected to further promote the application of PLNPs in tumour treatment. [ABSTRACT FROM AUTHOR]

Anode reversal is a detrimental phenomenon that occurs in proton exchange membrane fuel cells (PEMFCs) when the anode is subject to fuel starvation, leading to irreversible damage. This is a critical issue for the commercialization of PEMFCs. However, the development of more robust anode catalysts has been limited by the need for membrane electrode assembly (MEA)-level testing, which is costly and time-consuming. Here, we propose two accelerated stress test (AST) protocols based on widely available rotating disc electrode (RDE) methods to determine their suitability for screening anode catalysts and predicting MEA-level durability. One method is based on a carbon corrosion (cc) voltage cycling protocol between 1.0 and 1.5 V vs. RHE, while the other is a chronopotentiometry (cp) method. We evaluate three model catalysts (Pt30, Pt50, and Pt70) at the MEA-level through standard reversal testing and at the RDE-level using the two AST protocols (RDE-cc and RDE-cp). We find that both RDE-level methods can reliably predict MEA-level anode durability, and can be used by materials scientists to screen the relative durability of new anode catalysts. Our results also suggest Pt70 is a promising candidate for anode reversal tolerant PEMFCs, as it shows superior durability under both MEA-level and RDE-level tests. [Display omitted] • Provides a simple and effective way to screen new anode catalysts. • Rotating disc electrode (RDE) methods can reliably predict anode durability. • RDE can evaluate impact of oxygen evolution reaction catalysts on anode durability. [ABSTRACT FROM AUTHOR]

Oxygen evolution reaction (OER) is a well-known gas-involved reaction in which oxygen bubbles are formed and adhered on anode surface to lead to a sharp decline of performance. Iridium oxide (IrO 2) is the catalyst for water oxidation and is often used as a benchmark material. However, the factors affecting the bubbles detachment of IrO 2 are still unclear. Herein, we found that: 1. Nafion®, one of the main components of PEM membrane and usually used as electrode binder, can significantly increase the hydrophobicity of the electrode surface and is unfavorable to bubble detachment. 2. IrO 2 itself has good hydrophilicity but is not enough for efficient bubble separation, and no obvious linear relationship between bubble detachment performance and the particle size. 3. For improving bubble separation, irregularly rough surfaces should be avoided to prevent cavities trapping effect and multiple unnecessary bubble adhesion sites, both of which play the roles in stabilizing bubbles. In contrast, the uniformity and regularity of electrode surface should be paid more attention, as evidenced by comparing the surface morphology between drop-casting and pyrolysis in IrO 2 and RuO 2. • Nafion® can significantly enhance the hydrophobicity of the electrode surface and can't conducive to bubbles detachment. • Smaller particles tendency to facilitate bubbles detachment. • Amorphous IrO 2 can cause poor bubbles separation performance probably due to the surface of abundance g-OH. • Surface uniformity can enhance bubbles separation which is beneficial to the efficiency of the OER. [ABSTRACT FROM AUTHOR]

This work demonstrates the application of high-resolution, 3D imaging to characterize micro- and nano-scale features of iridium oxide (IrO 2) anode catalyst layers (CLs) in proton exchange membrane water electrolysis (PEMWE). Scanning electron microscopy (SEM) and nanoscale X-ray computed tomography (nano-CT) reveal differences in micro-scale features between spray-coated and blade-coated CLs, and in blade-coated CLs along the fabrication and testing timeline. The electrode thickness distribution of the tested blade-coated CL suggests increased thinning of regions compressed by titanium fibers of the porous transport layer (PTL). Ultra-high-resolution imaging of Xe-plasma focused ion beam with SEM (pFIB-SEM) with the development of a segmentation method is used to investigate nano-scale features between these regions of the tested blade-coated CL, showing variations in porosity and pore sizes. The findings provide insights and modeling inputs for the morphology of PEMWE anode CLs towards a better understanding of the relationship between fabrication, operation, and transport behavior. [Display omitted] • High-resolution, 3D, multi-scale imaging used to characterize PEMWE anode CLs. • SEM and nano-CT show increased thinning of tested CL regions due to PTL fibers. • 6 nm voxel size achieved with pFIB-SEM and in-house segmentation method developed. • "PTL-fiber-compressed" region in tested CL has lower porosity and smaller PSD. [ABSTRACT FROM AUTHOR]

Polymer membrane electrolyzers benefit from high‐pressure operation conditions and low gas cross‐over and can either conduct protons (H+) or hydroxide ions (OH−). Both types of electrolyzers have a similar design, but differ in power density and the choice of catalysts. Despite the significant endeavor of their optimization, to date, there is no well‐established impedance model for detailed analysis for either type of these devices. This complicates the in‐situ characterization of electrolyzers, hindering the investigation of degradation mechanisms and electrocatalytic processes as a function of applied current density or time. Nevertheless, a detailed understanding of such individual processes and distinguishing the performance‐limiting factors are the keystones for sophisticated device optimization. In this work, an impedance model based on electrode processes has been developed for an anion exchange membrane electrolyzer utilizing iridium oxide anode and platinum cathode electrocatalysts. This model allows to deconvolute the measured impedances into constituents related to the individual electrode processes and to estimate actual physico‐chemical quantities such as the reaction kinetic parameters and double‐layer capacitances. We discuss the meaning of the fitting parameters and show that this model enables, for the first time, the estimation of the electrochemically active surface area of the anode electrocatalysts under reaction conditions. [ABSTRACT FROM AUTHOR]

IrO2 is a current state-of-the-art catalyst for polymer electrolyte membrane water electrolyser (PEMWE) applications due to its high stability during the oxygen evolution reaction (OER). However, its activity needs to be significantly improved to justify the use of such a high-cost material. In this study, the activity of the IrO2 catalyst was improved by optimising and comparing two synthesis methods: the modified Adams fusion method (MAFM) and the molten salt method (MSM). Optimum OER performances of the IrO2 catalysts synthesised with the two synthesis methods were obtained at different temperatures. For the MAFM, a synthesis temperature of 350 °C produced the IrO2 catalyst with an overpotential of 279 mV and the highest OER stability of ~ 82 h at 10 mAcm-2. However, for the MSM, the lowest overpotential of 271 mV was observed for IrO2 synthesised at 350 °C, while the highest stability of ~ 75 h was obtained for the IrO2 synthesised at 500 °C. [ABSTRACT FROM AUTHOR]

Titanium dioxide (TiO2) is a high-performance material for emerging device applications, such as in resistive switching memories, in high-k capacitors, or, due to its flexoelectricity, in micro/nano-electro-mechanical systems. Enhanced electrical properties of TiO2 are ensured, especially by a careful selection of the bottom electrode material. Iridium dioxide (IrO2) is an excellent choice, as it favors the high-k rutile phase growth of TiO2. In this study, we introduce the fabrication of IrO2/TiO2/IrO2 capacitors and thoroughly characterize their electrical behavior. These capacitors show a dielectric constant for low temperature sputtered TiO2 of ∼70. From leakage current measurements, a coupled capacitive–memristive behavior is determined, which is assumed due to the presence of a reduced TiO2−x layer at the IrO2/TiO2 interface observed from transmission electron microscopy analyses. The memristive effect most probably originates from trapping and detrapping of electric charges in oxygen vacancy defects, which themselves can be generated and annihilated through an applied electric field, subsequently changing the resistance of the capacitor. The electric degradation type is identified as a filament-forming mechanism. Additionally, the temperature dependence of the leakage current is measured, demonstrating that the temperature behavior is strongly influenced by the ambient atmosphere. The latter dependency leads to the hypothesis that the oxygen evolution reaction of water incorporated in the IrO2/TiO2 interface passivates vacancies, thus significantly impacting the vacancy density in TiO2 and, as a further consequence, the electrical performance. [ABSTRACT FROM AUTHOR]

A sequential chlorination and electrochemical reduction process is demonstrated to convert Na–doped iridium oxide nanoparticles into useful IrIIICl 6 3− (aq) serving as the precursor for the fabrication of bio–stimulating electrode. The Na–doped iridium oxide nanoparticles are treated in 35 wt% hydrochloric acid at 70 °C for 18 h to form IrIVCl 6 2− (aq) with pH of 0.3, so the latter could be readily reduced to IrIIICl 6 3− (aq) at a potentiostatic mode of 0.6 V (vs. SCE). The oxidation state and the nature of complexing ligands for the regenerated IrIIICl 6 3− and IrIVCl 6 2−, as well as commercially available IrIIICl 6 3− are validated by X–ray Absorption Spectroscopy. UV–Vis profiles of regenerated IrIVCl 6 2− (aq) are recorded and the absorbance at 487 nm signal is benchmarked against that of standard IrIVCl 6 2− (aq) to obtain the effective regeneration ratio of 68.6%. X–ray diffraction patterns of Na–doped iridium oxide nanoparticles before and after the annealing treatment indicate the amorphous structure facilitates the chlorination step. The regenerated IrIIICl 6 3− is reused to synthesize Na–doped iridium oxide thin film serving as a bio–stimulating electrode for implantable bio–electronics. The regenerated Na–doped iridium oxide thin film reveals a charge-storage capacity of 0.32 mC/cm2-nm and impressive stability that are comparable to those of fresh Na–doped iridium oxide thin film derived from commercially available IrIIICl 6 3−. [ABSTRACT FROM AUTHOR]

Platinum alloys are highly efficient electrocatalysts for the oxygen reduction reaction (ORR) in acidic conditions. However, these alloys are susceptible to metal loss through leaching and degradation, leading to reduced catalyst stability and activity. Recently, it has been shown that doping with oxophilic elements can significantly alleviate these problems, with a prominent example being Mo‐doped Pt alloys. Here, to achieve atomic scale understanding of the exceptional activity and stability of these alloys, we present a detailed density functional theory description of the dopants' structures and impact on electrocatalyst properties. Beginning with the Mo/Pt system, we demonstrate that Mo can be stabilized in the form of low‐dimensional oxyhydroxide moieties on Pt defects. The resulting structures enhance stability and activity via distinct physical processes, with the Mo moieties both directly inhibiting Pt dissolution at defects and indirectly enhancing ORR activity by generation of strain fields on surrounding Pt terraces. We then generalize these analyses to other metal dopant elements, and we demonstrate that similar low‐dimensional oxyhydroxide structures control the electrocatalytic properties through an intricate interplay of the structures' acid stability, intrinsic activity for the ORR, and ability to induce ORR‐promoting strain fields on Pt. [ABSTRACT FROM AUTHOR]

The catalyst layers of proton exchange membrane water electrolyzer are generally made by coating ink mixtures of catalyst and ionomer to the membrane. The particle size and stability of such inks are crucial to the formation of the catalyst layer's microstructure and overall cost. In this paper, the characteristics and stability of iridium oxide inks are investigated. The effects of inks dispersed by sonication and ball-milling on the particle size distribution, zeta potential, and viscosity of the catalyst inks are investigated. For both dispersion methods, it is found that increasing the dispersion time and strength effectively reduces the average particle size as expected. The inks prepared by ball-milling tend to have narrower and smaller size distribution than those by sonication. The rheological behavior of these inks is found to be slightly non-Newtonian. Ball-milling appears to increase the ink viscosity. A dual-dispersion technique that combines both dispersion steps is developed in the present study. The inks made with this procedure yield smaller size distributions than those with single dispersion, thus a higher specific catalyst area that can reduce catalyst loading and cost. These inks are also found to have a long shelf life remaining homogeneous. • Fabrication methods for highly stable iridium oxide catalyst inks are developed. • Particle size distributions for inks dispersed by various methods are compared. • A dual-dispersion procedure is found to produce highly stable inks. [ABSTRACT FROM AUTHOR]

PEMWE is becoming one of the most promising technologies for efficient and green hydrogen production, while the anode OER process is deeply restricted by the now commercially used iridium oxide with sluggish reaction kinetics and super high cost. Deeply exploring the essential relationship between the underlying substrate materials and the performance of PEMWE cells while simultaneously excavating new practical and convenient methods to reduce costs and increase efficiency is full of challenges. Herein, two representative kinds of iridium oxide were studied, and their performance difference in PEMWE was precisely analyzed with electrochemical techniques and physical characterization and further linked to the ionomer/catalyst compound features. A novel anode with a uniform thin ionomer coating was successfully constructed, which simultaneously optimized the ionomer/catalyst aggregates as well as electrical conductivity, resulting in significantly enhanced PEMWE performance. This rigorous qualitative analysis of the structure–performance relationship as well as effective ionomer-affinitive optimization strategies are of great significance to the development of next-generation high-performance PEM water electrolyzers. [ABSTRACT FROM AUTHOR]

Pyrochlore ruthenates are highlighted as candidates to replace iridium oxide as oxygen evolution reaction (OER) electrocatalyst, but their designable geometric configurations and composition modulations are hampered by the high‐temperature (≈1100 °C) and long‐time calcination (more than 12 h), which further decreases the technical and economic feasibility. In this work, an energy‐ and time‐saving approach is proposed to prepare pyrochlore yttrium ruthenate at a much lower calcination temperature (600 °C) and shorter calcination time (6 h) just by inducing A‐site substitutions of lead ions (YPRO). The local microstrain derived from Pb provides the surficial compression and extra driving force to overcome the strain energy of phase‐transition resistances and the obtained low‐temperature YPRO exhibits enriched pores, deficient geometries, shortened Ru─O bond, and enlarged Ru─O─Ru bond angle, which further modify the electronic structure, involving of the rearranged band alignment and the eliminated bandgap. The regulated morphologic, geometric, and electronic structures in YPRO synergically boost the electrocatalytic OER performance (4.8‐fold and 30.0‐fold enhancements compared with pyrochlore yttrium ruthenate and commercial iridium dioxide (IrO2), respectively) in universal pH conditions. This substitution‐induced strain engineering on phase transition should also be effective for other high‐temperature materials and trigger their diverse intriguing properties. [ABSTRACT FROM AUTHOR]

The use of ZrO2 as a support material for IrOx‐based catalysts in oxygen evolution reaction (OER) electrocatalysis was studied using ex‐situ characterization and rotating disk electrode electrochemical testing of supported IrxZr(1‐x)O2 on ZrO2 of varying sizes. The catalyst exhibited high OER mass (specific) activity (712 A·gIr-1 ${ \cdot {\rm{g}}_{{\rm{Ir}}}^{ - 1} }$) and intrinsic activity (4.8 mA·cmESCA-2 ${ \cdot {\rm{cm}}_{{\rm{ESCA}}}^{ - 2} }$) at 1.6 VRHE, attributed to IrxZr(1‐x)O2 alloy formation, an interconnected network of Irx Zr(1‐x)O2 nanoparticles and the presence of Ir(III)/Ir(IV) species throughout the bulk. It also appears to be resistant to Ir dissolution; however, accumulation of O2 bubbles in the catalyst microstructure and minor phase transformation of Ir(III)/Ir(IV) species during OER cause deactivation. Temperature‐programmed desorption indicated a possible link between the observed high activity and higher amounts of adsorbed H2O and desorbed O2 species. [ABSTRACT FROM AUTHOR]

To increase the efficiency of hydrogen production by proton exchange membrane water electrolyzers (PEMWEs), the relationships between the specific activity and stability of the membrane–electrode assembly (MEA) must be clarified. Ir oxide electrodeposited on Ti substrate is used as an oxygen electrode, and its electronic properties and electrochemical behavior in PEMWE operation are observed. The electrode, fabricated through a facile strategy based on annealing in the air atmosphere, enhances the specific oxygen evolution reaction (OER) activity and stability in PEMWE operation. Furthermore, the electronic catalyst–substrate interactions associated with different reducibilities in the heteroatom system are studied. The morphology, electronic properties, and chemical state of the oxygen electrode are investigated through X‐ray spectroscopy, microscopy techniques, and computational analyses. Thermal treatment of the catalyst‐coated substrate decreases the bulk oxidation state of Ir and increases the surface oxidation state. According to the electrochemical and physical behavior analyses of PEMWEs, the oxygen content in the Ir oxide structure, which defines the OER activity and its stability, is influenced by the crystalline structure and formation of a stable interface between the catalyst and substrate. The outcomes can facilitate the development of strategies for enhancing the performance of PEMWEs and designing rational MEAs. [ABSTRACT FROM AUTHOR]

A paper-based electrochemical dual-function biosensor capable of determining pH and TCO2 was synthesized for the first time using an iridium oxide pH electrode and an all-solid-state ion electrode (ASIE). In the study, to obtain highly reliable results, the biosensor was equipped with a real-time pH correction function before TCO2 measurements. Compared to traditional liquid-filling carbon dioxide detection sensors, the utilization of ferrocene endows our novel sensor with abundant positive sites, and thus greatly improves its performance. Conversely, the introduction of MXene with conductivity close to that of metals reduces electrode resistance, which is beneficial for accelerating the electrochemical reaction of the sensor and reducing LOD. After optimization, the detection range of TCO2 is 0.095 nM–0.66 M, with a detection limit of as low as 0.023 nM. In addition, the sensor was used in real serum sample-spiked recovery experiments and comparison experiments with existing clinical blood gas analyzers, which confirmed the effectiveness of its clinical application. This study provides a method for the rational design of paper-based electrochemical biosensors and a new approach for the clinical detection of blood carbon dioxide. [ABSTRACT FROM AUTHOR]

Part I (1) introduced state-of-the-art proton exchange membrane (PEM) electrolysers with iridium-based catalysts for oxygen evolution at the anode in green hydrogen applications. Aqueous model systems and full cell testing were discussed along with proton exchange membrane water electrolyser (PEMWE) catalyst degradation mechanisms, types of iridium oxide, mechanisms of iridium dissolution and stability studies. In Part II, we highlight considerations and best practices for the investigation of activity and stability of oxygen evolution catalysts via short term testing. [ABSTRACT FROM AUTHOR]

State-of-the-art proton exchange membrane (PEM) electrolysers employ iridium-based catalysts to facilitate oxygen evolution at the anode. To enable scale-up of the technology to the terawatt level, further improvements in the iridium utilisation are needed, without incurring additional overpotential losses or reducing the device lifetime. The research community has only recently started to attempt systematic benchmarking of catalyst stability. Short term electrochemical methods alone are insufficient to predict catalyst degradation; they can both underestimate and overestimate catalyst durability. Complementary techniques, such as inductively coupled plasma-mass spectrometry (ICP-MS), are required to provide more reliable assessment of the amount of catalyst lost through dissolution. In Part I, we critically review the state of the art in probing degradation of iridium-based oxide catalysts. [ABSTRACT FROM AUTHOR]

Implantable electrodes are crucial for stimulation safety and recording quality of neuronal activity. To enhance their electrochemical performance, electrodeposited nanostructured platinum (nanoPt) and iridium oxide (IrOx) have been proposed due to their advantages of in situ deposition and ease of processing. However, their unstable adhesion has been a challenge in practical applications. This study investigated the electrochemical performance and stability of nanoPt and IrOx coatings on hierarchical platinum-iridium (Pt-Ir) substrates prepared by femtosecond laser, compared with the coatings on smooth Pt-Ir substrates. Ultrasonic testing, agarose gel testing, and cyclic voltammetry (CV) testing were used to evaluate the coatings' stability. Results showed that the hierarchical Pt-Ir substrate significantly enhanced the charge-storage capacity of electrodes with both coatings to more than 330 mC/cm2, which was over 75 times that of the smooth Pt-Ir electrode. The hierarchical substrate could also reduce the cracking of nanoPt coatings after ultrasonic, agarose gel and CV testing. Although some shedding was observed in the IrOx coating on the hierarchical substrate after one hour of sonication, it showed good stability in the agarose gel and CV tests. Stable nanoPt and IrOx coatings may not only improve the electrochemical performance but also benefit the function of neurobiochemical detection. [ABSTRACT FROM AUTHOR]

A major challenge with water splitting technology is to develop highly active and stable electrocatalysts for the oxygen evolution reaction (OER). IrO2 – based electrocatalysts are one of the most active electrocatalysts for proton exchange membrane (PEM) electrolysers, due to their excellent activity for the OER in acidic conditions. However, IrO2 often suffers from dissolution during electrolysis due to phase transitions into more soluble forms. Herein, a range of electrodeposited IrO2 films annealed to different temperatures of up to 500°C are prepared to understand the influence that crystalline/amorphous interfaces have on performance during accelerated degradation tests in concentrated acidic solutions. This study showed that an IrO2 film annealed at 300 °C exhibited the highest catalytic activity with a low overpotential of 150 mV at 10 mA cm−2, the smallest Tafel slope of 51 mV dec−1, with a less progressive decay in activity over a period of 8 h of accelerated degradation testing. This contrasts with both fully amorphous or more crystalline IrO2 films that decayed much more rapidly within 1 h of testing indicating the role that amorphous/crystalline regions have on OER performance. [ABSTRACT FROM AUTHOR]

In this work, the pH sensor electrode based on iridium oxides (IrOx) was developed and applied to potentiometric titration, instead of the traditional glass membrane electrodes, with its dominant features such as easy-implementation, low-cost and small-size. The electrode consisting of the IrOx layered on the surface of titanium substrate was fabricated by an anodizing method. Such electrode (IrOx/Ti) was highly sensitive to a pH change in a solution, but not in the presence of oxidizing or reducing agents. With the aim to minimize these chemical interferences, the IrOx/Ti electrode was covered by a nafion thin-film via a dip-coating method, namely Nf-IrOx/Ti. Besides the high mechanical stability, the Nf-IrOx/Ti sensing electrode indicated a linear correlation between the potential and the solution pH in the range of pH 2-12, with the response time of 120 s for an equilibrium. Although the response time of such pH electrode was quite longer than those of IrOx/Ti (60 s) and the commercial glass membrane electrode (30 s), the Nf-IrOx/Ti electrode permitted determining the equivalence points in acid-base potentiometric titrations with a high accuracy (less than 1 % relative errors in comparison with the corresponding values obtained by the commercial glass membrane electrode). [ABSTRACT FROM AUTHOR]

IrO2 is a current state-of-the-art catalyst for polymer electrolyte membrane water electrolyser (PEMWE) applications due to its high stability during the oxygen evolution reaction (OER). However, its activity needs to be significantly improved to justify the use of such a high-cost material. In this study, the activity of the IrO2 catalyst was improved by optimising and comparing two synthesis methods: the modified Adams fusion method (MAFM) and the molten salt method (MSM). Optimum OER performances of the IrO2 catalysts synthesised with the two synthesis methods were obtained at different temperatures. For the MAFM, a synthesis temperature of 350 °C produced the IrO2 catalyst with an overpotential of 279 mV and the highest OER stability of ~ 82 h at 10 mAcm−2. However, for the MSM, the lowest overpotential of 271 mV was observed for IrO2 synthesised at 350 °C, while the highest stability of ~ 75 h was obtained for the IrO2 synthesised at 500 °C. Significance: IrO2 is still currently a state-of-the-art catalyst in PEMWE due to its high stability in the highly acidic and oxidising conditions of the OER. High-performance IrO2 catalysts were successfully produced via the MAFM and MSM. Both the MAFM and MSM are simple and easily scalable for high-volume production of metal oxide catalysts. This study showed that the physical/structural properties of the IrO2 catalysts can be tailored through synthesis methods and synthesis conditions to improve their OER performance.

pH regulation in human biofluids is a crucial step for disease diagnosis and health monitoring. Traditional pH sensors are limited by their bulky size in wearable systems, and fragile glass tips require frequent calibration, thus limiting their use in continuous monitoring. Flexible sensors, particularly those utilizing microwires and thread-based substrates, present advantages for small sample analysis, including natural breathability and suitability for bandage or textile integration. This study examines iridium oxide and silver–silver chloride coated on thin gold wires, fabricated using sol–gel and dip-coating processes known for their simplicity. The flexible microwires demonstrated promising pH performance from a study of their pH characteristics, sensitivity, hysteresis, and potential drift. Electrodes tested in microwells allowed for small sample volumes and localized pH measurement in a controlled environment. Additional integration into fabrics for sweat sensing in wearables highlighted their potential for continuous, real-time health monitoring applications.