Mild Thermal Annealing Research Articles

Additive-Free Gelation of Graphene Oxide Dispersions via Mild Thermal Annealing: Implications for 3D Printing and Supercapacitor Applications.

Herein, a mild thermal annealing (MTA) process is presented for additive-free gelation of graphene oxide (GO) dispersions. This process transitions the GO from a nematic liquid crystal phase to a random network structure, significantly enhancing its rheological properties by order of magnitude. This transition is facilitated by the diffusion of functional groups on the GO surface, which induces hydrophobic attractions, leading to a stable network structure. Employing rheo-SAXS experiments, detailed insights are provided into the microstructural changes of GO gel under shear stress, establishing a direct correlation between its rheological behavior and microstructure. The distinctive properties of MTA-processed inks are illustrated, seamlessly integrating with 3D printing, to yield a highly porous lattice structure that demonstrates promising potential as a supercapacitor electrode. The MTA process, an additive-free approach to gelation, maintains the inherent dispersion properties of GO while offering scalability. Thus, this method brings significant economic and environmental advantages compared to conventional gelation techniques. The findings not only advance the fundamental understanding of 2D colloidal network gels but also increase the potential of GO for a wide range of applications, from gas and liquid absorbers to electrodes for energy storage and conversion, and biomedical fields.

Sol–gel prepared ZnO: UV irradiation effect on structure and surface properties

The effect of UV irradiation on sol–gel prepared ZnO films subjected to mild thermal annealing was investigated, with special attention to their structural and surface properties. Sol–gel processes, including a high-temperature annealing stage, have been adapted to the requirements of flexible electronics for in situ synthesis of semiconductor ZnO films on polymer substrates at lower temperatures due to UV irradiation. Application of UV radiation with emission peaks at 185 and 254 nm to films annealed at 180 °C made it possible to obtain ZnO films with Zn/O ratios of ca. 1, which cannot be achieved by heat treatment alone.

Revival of Degraded CsPbI3 Nanocrystals by Diselenide Ligand and Nanocrystal Self-Assembly on Nanofibrilar Ligand Template.

Among the lead halide perovskite (LHP) family, CsPbI3 is known to be significantly vulnerable to moisture, which hinders its use in real device applications. It is reported that chalcogen-based ligands can better stabilize CsPbI3 and revive nanocrystals (NCs). Here, diphenyl diselenide (DPhDSe) ligand is used to revive the degraded CsPbI3 NCs through a post-synthetic treatment of adding a small amount of DPhDSe in the degraded NC dispersion. DPhDSe in the dispersion formed nanofibrillar crystals at a low temperature through the π-π stacking of the phenyl ring. The nanofibrils played as a template on which the NCs self-assembled and they are attached side-by-side to form microfibers. The microfiber powder containing the NCs is optically stable at ambient conditions and morphologically self-healable by mild thermal annealing due to the dynamic Se─Se bond. The mechanism of the structural changes, optical transitions, and chemical changes has been systematically characterized through electron microscopy, diffraction, spectroscopy, and elemental analysis.

Transforming an Ionic Conductor into an Electronic Conductor via Crystallization: In Situ Evolution of Transference Numbers and Structure in (La,Sr)(Ga,Fe)O3‐x Perovskite Thin Films

AbstractMixed‐conducting perovskites are workhorse electrochemically active materials, but typical high‐temperature processing compromises their catalytic activity and chemo‐mechanical integrity. Low‐temperature pulsed laser deposition of amorphous films plus mild thermal annealing is an emerging route to form homogeneous mixed conductors with exceptional catalytic activity, but little is known about the evolution of the oxide‐ion transport and transference numbers during crystallization. Here the coupled evolution of ionic and electronic transport behavior and structure in room‐temperature‐grown amorphous (La,Sr)(Ga,Fe)O3‐x films as they crystallize is explored. In situ ac‐impedance spectroscopy with and without blocking electrodes, simultaneous capturingsynchrotron‐grazing‐incidence X‐ray diffraction, dc polarization, transmission electron microscopy, and molecular dynamics simulations are combined to evaluate isothermal and non‐isothermal crystallization effects and the role of grain boundaries on transference numbers. Ionic conductivity increases by ≈2 orders of magnitude during crystallization, with even larger increases in electronic conductivity. Consequently, as crystallinity increases, LSGF transitions from a predominantly ionic conductor to a predominantly electronic conductor. The roles of evolving lattice structural order, microstructure, and defect chemistry are examined. Grain boundaries appear relatively nonblocking electronically but significantly blocking ionically. The results demonstrate that ionic transference numbers can be tailored over a wide range by tuning crystallinity and microstructure without having to change the cation composition.

Facile Preparation Method of TiO2/Activated Carbon for Photocatalytic Degradation of Methylene Blue.

The development of nanocomposite photocatalysts with high photocatalytic activity, cost-effectiveness, a simple preparation process, and scalability for practical applications is of great interest. In this study, nanocomposites of TiO2 Degussa P25 nanoparticles/activated carbon (TiO2/AC) were prepared at various mass ratios of (4:1), (3:2), (2:3), and (1:4) by a facile process involving manual mechanical pounding, ultrasonic-assisted mixing in an ethanol solution, paper filtration, and mild thermal annealing. The characterization methods included XRD, SEM-EDS, Raman, FTIR, XPS, and UV-Vis spectroscopies. The effects of TiO2/AC mass ratios on the structural, morphological, and photocatalytic properties were systematically studied in comparison with bare TiO2 and bare AC. TiO2 nanoparticles exhibited dominant anatase and minor rutile phases and a crystallite size of approximately 21 nm, while AC had XRD peaks of graphite and carbon and a crystallite size of 49 nm. The composites exhibited tight decoration of TiO2 nanoparticles on micron-/submicron AC particles, and uniform TiO2/AC composites were obtained, as evidenced by the uniform distribution of Ti, O, and C in an EDS mapping. Moreover, Raman spectra show the typical vibration modes of anatase TiO2 (e.g., E1g(1), B1g(1), Eg(3)) and carbon materials with D and G bands. The TiO2/AC with (4:1), (3:2), and (2:3) possessed higher reaction rate constants (k) in photocatalytic degradation of methylene blue (MB) than that of either TiO2 or AC. Among the investigated materials, TiO2/AC = 4:1 achieved the highest photocatalytic activity with a high k of 55.2 × 10-3 min-1 and an MB removal efficiency of 96.6% after 30 min of treatment under UV-Vis irradiation (120 mW/cm2). The enhanced photocatalytic activity for TiO2/AC is due to the synergistic effect of the high adsorption capability of AC and the high photocatalytic activity of TiO2. Furthermore, TiO2/AC promotes the separation of photoexcited electron/hole (e-/h+) pairs to reduce their recombination rate and thus enhance photocatalytic activity. The optimal TiO2/AC composite with a mass ratio of 4/1 is suggested for treating industrial or household wastewater with organic pollutants.

Influence of Pt Ultrathin Interlayers on Magnetic Anisotropy in Ni/NiO Multilayers

Perpendicular magnetic anisotropy at transition metal/oxide interfaces plays a significant role in technological applications such as magnetic storage and spintronics. In this study, we investigate the effects of thermal annealing and Pt ultrathin interlayers on the magnetic anisotropy in Ni/NiO multilayers. Ni/NiO/Pt multilayers were fabricated via radiofrequency magnetron sputtering and natural oxidation. The static magnetic properties of the samples were studied using temperature-dependent SQUID magnetometry. We focus on a sample with a Nickel thickness of 6.7 nm in each multilayer period. This multilayer in Ni/NiO form showed the maximum enhancement of perpendicular magnetic anisotropy after mild thermal annealing in past work. In this work, we study the effects of ultrathin Pt interlayers on the magnetic properties of such a Ni/NiO multilayer before and after annealing. We have observed a further increase in perpendicular magnetic anisotropy, and we study the temperature-dependent magnetic properties of this system, which combines the favorable magnetic properties of Ni/Pt and Ni/NiO multilayers.

Fabrication of Hydroxyl‐Group‐Rich Reduced Graphene Oxide Film and its Application for Electrochemical Detection of Hydrogen Peroxide

AbstractGraphene oxide (GO) can be obtained economically from graphite, and it has, therefore, been used for energy storage, conversion, and biosensor fabrication. To overcome the limitations associated with the poor electrical conductivity of GO, mild thermal reduction is widely used. However, owing to considerable variations in GO in terms of size and shape, uniform reduction of GO films is highly challenging. Herein, it reports a mildly reduced uniform graphene oxide thin film (mrUG) that is enriched with functional hydroxyl groups. This film is effective for electrochemical H2O2 decomposition and detection. A uniform graphene oxide thin film (UGTF) is first fabricated on an indium tin oxide (ITO) substrate and subjected to mild thermal annealing at 300 °C. Remarkably, the variations in all important parameters, including film thickness, surface roughness, reduction level, are significantly low in the case of mrUG. Moreover, It is found that unlike GO, UGTF undergoes structural rearrangement easily and possesses many hydroxyl groups (─OH) when reduced for a specific duration (t = 10 s, mrUG(10)). mrUG(10) is highly stable and effectively decomposed H2O2, which is advantageous for the electrochemical detection of H2O2 with extremely low signal variations. Therefore, mrUG(10) can be used as a carbon‐based metal‐free electrocatalyst in biosensors, energy, and electronic applications.

Uniform Gold Nanostructure Formation via Weakly Adsorbed Gold Films and Thermal Annealing for Reliable Localized Surface Plasmon Resonance-Based Detection of DNase-I.

Deoxyribonuclease-I (DNase-I), a representative endonuclease, is an important biomarker for the diagnosis of infectious diseases and cancer progression. However, enzymatic activity decreases rapidly ex vivo, which highlights the need for precise on-site detection of DNase-I. Here, a localized surface plasmon resonance (LSPR) biosensor that enables the simple and rapid detection of DNase-I is reported. Moreover, a novel technique named electrochemical deposition and mild thermal annealing (EDMIT) is applied to overcome signal variations. By taking advantage of the low adhesion of gold clusters on indium tin oxide substrates, both the uniformity and sphericity of gold nanoparticles are increased under mild thermal annealing conditions via coalescence and Ostwald ripening. This ultimately results in an approximately 15-fold decrease in LSPR signal variations. The linear range of the fabricated sensor is 20-1000ngmL-1 with a limit of detection (LOD) of 127.25 pgmL-1 , as demonstrated by spectral absorbance analyses. The fabricated LSPR sensor stably measured DNase-I concentrations from samples collected from both an inflammatory bowel disease (IBD) mouse model, as well as human patients with severe COVID-19 symptoms. Therefore, the proposed LSPR sensor fabricated via the EDMIT method can be used for early diagnosis of other infectious diseases.

Assessing the evolution of oxygenated functional groups on the graphene oxide surface upon mild thermal annealing in water.

Graphene oxide (GO) is known to be a 2D metastable nanomaterial that can be reconstructed under thermal annealing into distinct oxidized and graphitic phases. Up to now, such phase transformation, mainly related to epoxide and hydroxyl functional groups, has been usually achieved by thermally treating layers of GO in the solid state. Here, we present the mild annealing of GO dispersed in an aqueous medium, performed at two temperatures, 50 °C and 80 °C, for different intervals of time. We show experimental evidences of the epoxide instability in the presence of water by means of XPS, cyclic voltammetry and Raman spectroscopy, demonstrating the reorganization of epoxide and hydroxyl moieties initiated by water molecules. In fact, at 50 °C an increase in oxygen content is detected in all annealed samples compared to untreated GO, with a transformation of epoxide groups into vicinal diols. On the other hand, at 80 °C the oxygen content decreases towards the initial value since the vicinal diols, previously formed, transform into single hydroxyls and C[double bond, length as m-dash]C bonds. Moreover, the higher temperature annealing likely favours oxygenated functional groups rearrangements and clustering, in accordance with the literature, leading to a higher electron affinity and conductivity of the graphenic network.

P-type conversion of distorted SnOx thin film by mild thermal annealing treatment in pure N2 environment

Tin oxide semiconductors can achieve both n- and p-type conduction, depending on the oxidation state of Sn. An n-type conduction can easily be fabricated; however, considerable optimization is required for fabrication of a p-type behavior. In this study, n-type SnOx thin films, prepared by reactive magnetron sputtering, were converted to p-type behavior using only post-deposition annealing at 600 °C in a pure nitrogen atmosphere. The annealing-temperature-dependent electrical properties of the SnOx thin films led to a remarkable increase in the yield of p-type behavior at 600 °C. X-ray diffraction analysis revealed that the SnOx film had a SnO2-dominant crystal phase and also suggested that N2 molecules dissociated at 600 °C and filled the oxygen vacancy (VO) site as atomic nitrogen. A detailed analysis of the binding state by x-ray photoelectron spectroscopy confirmed an increase in SnO-derived components, the appearance of peaks derived from N–Sn bonding, a decrease in VO caused by nitrogen doping, and charge transfer. Thus, we found that addition of nitrogen atoms promotes a chemical shift from Sn4+ to Sn2+ and that simultaneously passivates VO and contributes to hole generation.

(Invited) Benchmarking Oxygen Evolution Reaction Activity and Stability of Unsupported and Supported IrOx Nanoparticles

Proton-exchange membrane water electrolyzers (PEMWEs) electrodes use scarce and costly platinum group metals (PGMs), but only such devices are able to meet the requirements associated with renewable energies (large amplitude and frequent and rapid variations in the current applied to the cell). Catalysts represent only 8 % to the overall stack cost, 6 % being associated with the high iridium (Ir) loading used to electrocatalyze the anodic oxygen evolution reaction (OER). High surface area supported Ir oxide (IrOx) catalysts thus represent a promising strategy to reduce the cost of this technology and limit the geological pressure on Ir. However, the Gibbs-Thompson effect, which controls the electrochemical stability of nanomaterials casts a doubt on the viability of this approach. To shed light into the benefits and limitations of supported and unsupported IrOx catalysts, we benchmarked commercial materials (unsupported IrO2, Ir/C), unsupported porous IrOx microparticles, and IrOx nanoparticles (NPs) supported on carbon black or on doped tin oxide aerogels (AG)/nanofibers (NFs). Transmission electron microscopy (TEM) and identical-location transmission electron microscopy (IL-TEM) provided changes in morphology during accelerated stress testing. Complementarily, a flow cell connected to an inductively-coupled mass spectrometer (FC-ICP-MS) was used to assess their stability number (S-number, see Figure 1). The results show that supported IrOx nanocatalysts are extremely active toward the OER because they feature mixed Ir oxidation states and a high density of active sites (small crystallite/particle size). The lack of robustness of their supports, however, prevents the nanocatalysts from sustaining this high OER activity [1, 2]. Similar to what was observed on extended surfaces, we report that mild thermal annealing (450°C) leads to lower Ir atom dissolution rate. Overall, the best compromise between OER activity and stability was obtained for unsupported porous IrOx microparticles after mild thermal annealing under air at 450°C [2]. On the cathode side, IL-TEM measurements revealed mild changes in morphology for Pt/C nanoparticles [3]. Ackowledgements This work was supported by the French National Research Agency in the frame of the MOISE project (grant number ANR-17-CE05-0033). References S. Abbou, R. Chattot, V. Martin, F. Claudel, L. Solà-Hernández, C. Beauger, L. Dubau, F. Maillard, ACS Catal. 10 (2020) 7283-7284.C. Daiane Ferreira da Silva, F. Claudel, V. Martin, R. Chattot, S. Abbou, K. Kumar, I. Jiménez-Morales, S. Cavaliere, D. Jones, J. Rozière, L. Solà-Hernandez, C. Beauger, M. Faustini, J. Peron, B. Gilles, C. Beauger, L. Piccolo, F. H. Barros de Lima, L. Dubau, F. Maillard, ACS Catal. 11 (2021) 4107-4116. A. Viola, L. Dubau, F. Maillard, in preparation. Figure 1. S-number values calculated for supported and unsupported IrOx electrocatalysts during a galvanostatic accelerated stress test (j = 10 mA cm-2 geo, T = 80 °C, U cut-off = 2 V vs. RHE) performed in Ar-saturated 0.05 M H2SO4. Reprinted with permission from ref. [2]. Copyright 2021 American Chemical Society. Figure 1

Growth, Magnetic Anisotropies and Exchange Bias of Thin Ni0.95Fe0.05/NiFeO Multilayers

Ni0.95Fe0.05/NiFeO multilayers were fabricated by radio frequency magnetron sputtering and natural oxidation. Doping of Ni by only 5 at. % Fe results in enhanced layering quality as X-ray reflectivity reveals. Due to magnetostatic anisotropy, the multilayers were found to be in-plane magnetized. The influence of mild thermal annealing (T = 525 K) on the magnetic properties of NiFe/NiFeO multilayers is also investigated. Annealing results in the enhancement of perpendicular magnetic anisotropy, mainly due to an increase in the uniaxial volume anisotropy term. Temperature-dependent hysteresis measurements between 4–400 K revealed considerable enhancement of coercivity and appearance of exchange bias effect.

Electronic Self-Passivation of Single Vacancy in Black Phosphorus via Ionization.

We report that monoelemental black phosphorus presents a new electronic self-passivation scheme of single vacancy (SV). By means of low-temperature scanning tunneling microscopy and noncontact atomic force microscopy, we demonstrate that the local reconstruction and ionization of SV into negatively charged SV^{-} leads to the passivation of dangling bonds and, thus, the quenching of in-gap states, which can be achieved by mild thermal annealing or STM tip manipulation. SV exhibits a strong and symmetric Friedel oscillation (FO) pattern, while SV^{-} shows an asymmetric FO pattern with local perturbation amplitude reduced by one order of magnitude and a faster decay rate. The enhanced passivation by forming SV^{-} can be attributed to its weak dipolelike perturbation, consistent with density-functional theory numerical calculations. Therefore, self-passivated SV^{-} is electrically benign and acts as a much weaker scattering center, which may hold the key to further enhance the charge mobility of black phosphorus and its analogs.

2+2] Cyclo-Addition Reactions for Efficient Polymerization on a HOPG Surface at Ambient Conditions.

Polymers obtained by on-surface chemistry have emerged as a class of promising materials. Here, we propose a new strategy to obtain self-assembled 1D polymers by using photochemical [2+2] cyclo-addition or by using a mild thermal annealing. All nanostructures are fully characterized by using scanning tunneling microscopy at ambient conditions on a graphite surface. We demonstrated that nature of the stimulus strongly alters the overall quality of the resulting polymers in terms of length and number of defects. This new way is an efficient method to elaborate on-surface self-assembled 1D polymers.

Manufacturing Free-Standing Graphene Oxide/Carbon Nanotube Hybrid Papers and Improving Electrical Conductivity by a Mild Annealing Treatment

The present work aims to evaluate the manufacturing processes of free-standing graphene oxide (GO)/reduced graphene oxide(rGO)/carbon nanotube (MWCNT) papers-like and the effect on electrical conductivities after annealing treatment. The pure GO and the hybrid papers were obtained by vacuum filtration and submitted to mild thermal annealing at 400 °C under an argon atmosphere. Analyses comparing the carbon paper-like materials before and after thermal treatment were done by thermogravimetric analysis (TGA), Raman spectroscopy, scanning electron microscopy (SEM), and electrical conductivity measurements. The characterization results show the annealing process effect on the morphology of paper materials. The GO papers and the hybrid (GO/rGO/MWCNT) exhibited good free-standing structure properties. The SEM results suggest the formation of gas void due to the thermal treatment. TGA and Raman results showed the thermal reduction and restoration of the carbon sp2 network of the graphene oxide induced by thermal treatment. The thermal treatment was responsible for changing the almost insulator characteristic of free-standing pure GO paper, achieving an electrical conductivity of 752 S/m, and improving 45% of the free-standing hybrid carbon nanomaterials papers (GO/rGO/MWCNT) electrical conductivity, achieving the value of 1020 S/m.

Effects of Thermally Induced Phase Transition on the Negative Thermo-Optic Properties of Atomic-Layer-Deposited TiO2Films

The negative thermo-optic properties of TiO2 have been considered promising for athermal photonic devices that can mitigate the optical-performance instability due to temperature variations. When temperature increases, its negative thermo-optic coefficient (TOC) can compensate for the unfavorable increase in refractive index exhibited by widely used optical materials such as Si, which have positive TOCs. Herein, the structure–property relationship of TiO2 is thoroughly investigated to understand the negative thermo-optic behaviors of TiO2. Through atomic layer deposition and mild thermal annealing, the obtained negative TOC values are as high as −2.30 × 10–4/°C in the visible to the near-infrared regime. X-ray diffraction/reflectivity and temperature-dependent refractive index measurements identify that the higher crystallinity of anatase TiO2 leads to greater negative TOC values due to its higher density and lower porosity, compared to those of amorphous or weakly crystalline states. The Prod’homme model and band gap analysis reveal that the effect of volume expansion is more dominant on the enhanced negative TOC of TiO2, rather than the polarizability. Photoelectron spectroscopy measurements suggest an amorphous relaxation process during annealing that further supports the amorphous-to-crystalline transformation in TiO2. The findings of the structure and chemical properties governing the negative TOC of TiO2 for athermal applications may be of significant relevance to many photonic devices showing strong performance instability due to the high positive TOCs.

Probing lattice defects in crystalline battery cathode using hard X-ray nanoprobe with data-driven modeling

Lattice defects, e.g., dislocations and grain boundaries, critically impact the properties of crystalline battery cathode materials. A longstanding challenge is to probe the meso‑scale heterogeneity and evolution of lattice defects with sensitivity to atomic-scale details. Herein, we tackle this issue with a unique combination of X-ray nanoprobe diffractive imaging and advanced machine learning techniques. The domains with different lattice defect configuration within a single-crystalline LiCoO2 cathode particle are faithfully revealed using our approach. We further visualize the rearrangement of grain boundaries and local crystallinity upon mild thermal annealing. These results pave a direct way to the understanding of crystalline battery materials’ response under external stimuli with high fidelity, which provides valuable empirical guidance to defect-engineering strategies for improving the cathode materials against aggressive battery operation.

Enhanced graphitic domains of unreduced graphene oxide and the interplay of hydration behaviour and catalytic activity

Previous studies indicate that the properties of graphene oxide (GO) can be significantly improved by enhancing its graphitic domain size through thermal diffusion and clustering of functional groups. Remarkably, this transition takes place below the decomposition temperature of the functional groups and thus allows fine tuning of graphitic domains without compromising with the functionality of GO. By studying the transformation of GO under mild thermal treatment, we directly observe this size enhancement of graphitic domains from originally ≤40 nm2 to >200 nm2 through an extensive transmission electron microscopy (TEM) study. Additionally, we confirm the integrity of the functional groups during this process by a comprehensive chemical analysis. A closer look into the process confirms the theoretical predicted relevance for the room temperature stability of GO and the development of the composition of functional groups is explained with reaction pathways from theoretical calculations. We further investigate the influence of enlarged graphitic domains on the hydration behaviour of GO and the catalytic performance of single atom catalysts supported by GO. Additionally, we show that the sheet resistance of GO is reduced by several orders of magnitude during the mild thermal annealing process.

Magnetic Aspects and Large Exchange Bias of Ni0.9Co0.1/NiCoO Multilayers

Ultrathin films of Ni0.9Co0.1 were grown by radio frequency magnetron sputtering. By means of a periodic natural oxidation procedure they were transformed into Ni0.9Co0.1/NiCoO multilayers. Room temperature hysteresis loops recorded via the magneto-optic Kerr effect have revealed over all in-plane magnetic anisotropy due to magnetostatic anisotropy. Mild thermal annealing at 250 °C enhanced a tendency for perpendicular magnetic anisotropy, mainly due to an increase of the uniaxial volume anisotropy term. Spin reorientation transition, exchange bias larger than 700 Oe, and strong coercivity enhancement were observed via a superconducting quantum interference device at low temperatures after field cooling.

(Invited) Benchmarking Oxygen Evolution Reaction Activity and Stability of Unsupported and Supported IrOx Nanoparticles

High investments and operational cost of proton-exchange membrane water electrolysers (PEMWE) devices are partly due to that of their constituting materials. In this context, research efforts are dedicated to minimize the content in iridium (Ir) used to electrocatalyze the oxygen evolution reaction (OER) at the anode. One possible materials’ strategy is to support iridium oxide nanoparticles (IrOx NPs) on a corrosion resistant support, such as antimony-doped (ATO), niobium-doped (NTO) or tantalum-doped (TaTO) tin oxide [1,2]. However, the Gibbs-Thompson effect, which controls the electrochemical stability of nanomaterials casts a doubt on the long-term relevance of this approach. To tackle these issues, we built a library of 18 supported and unsupported IrOx catalysts and established their stability number values using inductively-coupled plasma mass spectrometry (ICP-MS) and electrochemistry. Our results provide quantitative evidence that supported IrOx nanocatalysts are more active towards the OER but less stable than unsupported micrometer-sized catalysts. A large part of this instability comes from the metal oxide support which, by degrading, results in IrOx NPs being detached or electrically-disconnected (loss of doping element). In this respect, TaTO supports revealed substantially more stable than ATO supports [2]. Another reason for the drop in OER performance over the long term comes from the fact that IrOx NPs contain mixed valences including Ir atoms in (+III) oxidation state, which are highly active towards the OER but also prone to dissolve [1,3]. Similar to what was observed on extended surfaces, we report that mild thermal annealing (450°C) leads to lower Ir atom dissolution rate. Overall, the best compromise between OER activity and stability was obtained for unsupported porous IrOx microparticles after mild thermal annealing under air at 450°C [4]. Ackowledgements This work was supported by the French National Research Agency in the frame of the MOISE project (grant number ANR-17-CE05-0033). References F. Claudel, L. Dubau, G. Berthomé, L. Solà-Hernandez, C. Beauger, L. Piccolo, F. Maillard, ACS Catal. 9 (2019) 4688-4698.S. Abbou, R. Chattot, V. Martin, F. Claudel, L. Solà-Hernández, C. Beauger, L. Dubau, F. Maillard, ACS Catal. 10 (2020) 7283-7284.M. Scohy, S. Abbou, V. Martin, B. Gilles, E. Sibert, L. Dubau, F. Maillard, ACS Catal. 9 (2019) 9859-9869.C. Daiane de Ferreira, F. Claudel, V. Martin, R. Chattot, S. Abbou, I. Jiménez-Morales, S. Cavaliere, D. Jones, J. Rozière, L. Solà-Hernandez, C. Beauger, M. Faustini, J. Peron, B. Gilles, C. Beauger, L. Piccolo, F. H. Barros de Lima, L. Dubau, F. Maillard, submitted to ACS Catal.