Advances in smart technologies and the Internet of Things (IoT) require compact and efficient energy storage devices. Among microscale systems, RuO2-based micro-supercapacitors (MSCs) can deliver high-power pulses, but the limited stability window of their aqueous electrolytes restricts their energy density. This study investigated the use of pyrrolidinium-based protic ionic liquids (PILs) with different alkyl chain lengths and anion types to achieve pseudocapacitive charge storage in RuO2 MSCs with an extended cell voltage of up to 1.5 V. Of the tested electrolytes, 1-propyl pyrrolidinium trifluoroacetate [Pyr3H]*[TFA]- exhibited excellent energy density and cycling performance, and 1-methyl pyrrolidinium tetrafluoroborate [Pyr1H]*[BF4]- demonstrated low equivalent series resistance and superior power retention. The experimental findings were consistent with Reactive Force Field (ReaxFF) molecular dynamics simulations which revealed proton exchange and ion diffusion mechanisms in both ionic liquids. Ionogel-based MSCs demonstrated long-term cycling stability, retaining performance over 5000 charge/discharge cycles. These results highlight the potential of using pyrrolidiniumbased PILs in on-chip, solid-state MSCs to power microelectronics.

Hydrated ruthenium dioxide (RuO2) 2 ) stands out as the archetype of pseudocapacitive materials, renowned for its outstanding capacitance and remarkable stability for supercapacitor applications. Herein, we introduce a model of amorphous low-density hydrous RuO2 2 for supercapacitors, achieving 2.2 g cm-3 -3 density, utilizing a combined approach of ab initio molecular dynamics simulations (AIMD) and static calculations using the Nudged Elastic Band (NEB) technique, within the frame of density functional theory (DFT), making the first instance of such an approach. Starting from an anhydrous amorphous structure, we systematically increase hydration levels within the model. It is found that full hydration exhibits both the presence of more than one OH group per Ru atom in the structure and molecular water loading into RuO2 2 pores. Hydrogen diffusion is estimated at 7.05 . 05 x 10 -6 cm2 2 s-1 , -1 , which is further correlated with the specific presence of OH species located at non-bridging oxygen sites. They are shown to almost annihilate local hydrogen migration barriers (0.06 eV), while non dissociated water molecules insures hydrogen migration from distant sites via Grotthuss type of mechanisms (0.3-0.4 eV activation range). These findings provide valuable insights into the behavior of hydrated RuO2 2 in supercapacitors, shedding light on the statistical interplay between hydration and hydrogen motion for enhanced energy storage applications.

The rapid development of the Internet of Things (IoT) demands reliable and long-term energy supply to microelectronic devices distributed over the network with high power performance and less maintenance required. [1] Micro-supercapacitors (MSCs) have come to the foreground as miniaturized energy storage devices showing outstanding power density and long cycle life. However, the low cell voltage and low energy density remain major bottleneck that prevents their adoption in real device applications. To this end, several studies have been devoted to the engineering of MSC electrode materials and structural architecting of current collectors within the limited available footprint. This approach could offer opportunities to enhance the electrochemically active surface and mass loading of active materials with fast ion diffusion kinetics, leading to high areal energy density performance. [2] Although several efforts have been put forth in this direction, the complex synthesis route, unfavourable interfacial and mechanical stability of the electrode, electrolyte compatibility issues, etc. remain an arduous challenge. [3] The low cell voltage is another major issue preventing from achieving high energy density values in MSCs as it is directly linked to the electrochemical stability window (ESW) of the electrolytes used. [4] In addition, liquid-state electrolytes currently employed are inappropriate for the microfabrication route as it is prone to evaporation, leakage, and potential safety issues. Hence, a lot of research attention has been given to developing solid-state electrolytes able to afford large operational windows and help promote the application of on-chip MSCs. In this work, we have demonstrated the use of protic ionic liquid (PIL)-based electrolytes able to provide pseudocapacitance in hydrous ruthenium dioxide (RuO 2 ) electrodeposited on interdigitated MSC substrates with extended operational cell voltage. As a pseudocapacitive material, RuO 2 exhibits excellent conductivity, high electrochemical reversibility, and cycling stability. [5] On the other hand, as room temperature molten salts, PILs help to overcome evaporation and encapsulation problems associated with the conventional aqueous electrolytes and flammability and safety issues linked to common organic electrolytes. [6-9] We explored pyrrolidinium-based PILs with varying alkyl substitutions, their structure-property, and electrochemical studies for RuO 2 MSCs. To further expand the use of these PILs in real devices, 3D MSCs with higher active material mass loading was realised using interdigitated porous Au current collector substrates. The PIL-based porous RuO 2 MSCs showed superior charge storage and higher energy density performance as compared to conventional aqueous electrolytes. To envision the practical application of RuO 2 MSCs and their subsequent integration with microelectronic devices, ionogel-based solid-state electrolytes were developed. This work opens pathways to develop micro-supercapacitors exhibiting high energy and power density by combining pseudocapacitive metal oxide-based active materials and protic ionic-liquid-based non-aqueous electrolytes and help their integration with on-chip IoT devices. References [1] N. A. Kyeremateng, T. Brousse, D. Pech, Nat Nanotechnol 2017, 12, 7. [2] C. Lethien, J. Le Bideau, T. Brousse, Energ Environ Sci 2019, 12, 96. [3] Y. Li, S. Xiao, T. Qiu, X. Lang, H. Tan, Y. Wang, Y. Li, Energy Storage Mater 2022, 45, 741. [4] C. Zhong, Y. Deng, W. Hu, J. Qiao, L. Zhang, J. Zhang, Chem Soc Rev 2015, 44, 7484. [5] A. Ferris, S. Garbarino, D. Guay, D. Pech, Adv Mater 2015, 27, 6625. [6] D. Rochefort, A. L. Pont, Electrochem Commun 2006, 8, 1539. [7] M. Yoshizawa, W. Xu, C. A. Angell, J Am Chem Soc 2003, 125, 15411. [8] J. P. Belieres, C. A. Angell, J Phys Chem B 2007, 111, 4926. [9] J. S. Seenath, D. Pech, D. Rochefort, J Power Sources 2022, 548, 232040.

The enhanced areal energy of three-dimensional (3D) micro-supercapacitors has made these miniaturized energy-storage components increasingly important at the dawn of the Internet of Things. Although ultrahighcapacitances have been obtained with Ru-based pseudocapacitive materials, their substitution with abundant non-noble transition metals is a key requirement to reduce the price of electrochemical micro-storage systems and enable long-term sustainability. Here we report a cost-effective and industrially feasible approach to realize 3D micro-supercapacitors based on highly porous scaffolds of Ni/MnO2. These low-price electrodes exhibit a huge areal capacitance exceeding 4 F cm-2 and excellent cycling stability. In addition, extended cell voltages up to 2.6 V with areal energy of 1159 mJ cm-2 (i.e. 0.3 mWh cm-2) and high power of 11.1 mW cm-2 were achieved using innovative Na-based ionogel electrolytes. We also show a novel micro-supercapacitor design based on entangled porous Ni/MnO2 pillars, combining both energy and power ability on a small footprint area.

. The development of an efficient photocatalyst capable of producing enough hydrogen for applications in everyday life under direct sunlight exposure is still challenging. In this work, a new concept for a three-dimensional microstructured photocatalyst is proposed, in which a standard deep-reactive ion etching process allows for the optimization, fabrication and subsequent deposition of TiO 2 thin films by physical vapor deposition for H 2 production by direct water splitting. After the development of enlarged surface microstructures, the composition and morphology of the 3D TiO 2 photocatalyst were characterized by XRD, XPS, UV/Vis spectroscopy and SEM. Furthermore, the influence of the area enlargement factor on the 3D photocatalyst surface morphology and its photocatalytic performance under UV-visible irradiation was thoroughly analyzed and corroborated by electrochemical experiments. The photocatalyst exhibited an increase in H 2 production by almost a factor of 12 compared to conventional planar TiO 2 films. The H 2 production was further improved by a factor of 4 through the introduction of Au nanoparticles grown on top of the TiO 2 layer. The advantages and development of robust and hierarchical photocatalysts using microelectromechanical fabrication techniques are highlighted as potential solutions for a broad range of applications from photocatalysis, electronics, and sensing elements to 3D metamaterials.

Figures dataset for Journal of Power Sources 548 (2022) 232040

The rising growth of smart and autonomous microelectronic devices in the IoT (Internet of Things) era urges the development of advanced microscale energy sources with tailor-made features and customized energy/power requirements [1]. Micro-supercapacitors (MSCs) emerged as potential energy storage devices complementing micro-batteries to power ubiquitous sensor networks needed to foster the development of IoT. However, the low cell voltage and low energy density remain major bottleneck that prevents their application at a large scale in real devices. To mitigate this issue, several studies have been devoted to the engineering of MSC electrode materials and structural architecting of current collectors to enhance the surface area and areal energy density by considering the limited available footprint area [2]. This approach however has associated challenges such as complex synthesis route, the deleterious interfacial and mechanical stability of the electrode, and compatibility issues with the electrolyte and the current collector underneath [3]. Another important challenge to solve for reaching high energy density values in MSCs is the limited electrochemical stability window (ESW) of the electrolytes used as energy stored is directly related to the square of the cell voltage [4]. The electrolytes play a major role in deciding the ESW and liquid-state electrolytes currently employed are troublesome for the microfabrication process due to leakage, evaporation, and safety issues. Therefore, it’s imperative to develop alternative electrolytes including solid-state electrolytes reconcilable to the target application of MSCs. To address the low energy density challenge of current MSCs, we have developed interdigitated MSCs using hydrous ruthenium dioxide (RuO2) electrodes in combination with novel protic ionic liquid (PIL)-based electrolytes able to provide pseudocapacitance while affording a higher ESWs as compared to conventional aqueous electrolytes. As a state-of-the-art pseudocapacitive electrode material, RuO2 owns the key merits of excellent conductivity, high electrochemical reversibility, and cycling stability [5], whereas PILs could help alleviate issues facing currently used electrolytes such as evaporation and encapsulation problems pertaining to aqueous-based and flammability of common organic electrolytes [6], [7], [8]. In the next step, the slow proton transport kinetics of PILs were addressed by the doping of silicotungstic acid (SiWa, H4SiW12O40) with the PIL, which further boosted the pseudocapacitive current response with enlarged cell voltage. The real MSC device was realized by the use of RuO2 deposited on interdigitated porous Au current collectors having a high area enlargement factor (AEF) in combination with triethylammonium bis(trifluoromethanesulfonyl)imide (TEAH-TFSI)-based PIL. The resultant 3D MSC rendered a cell voltage exceeding 2V with areal capacitance as high as 86 mF cm-2 at 5 mV s-1 on par with the performance of 3D MSC tested using 0.5 M H2SO4 (cell voltage of 0.9 V and areal capacitance of 85 mF cm-2 at 5 mV s-1) but higher energy density performance (more than 4 times) using similar number of RuO2 deposition cycles. To demonstrate the potential integration in real on-chip device application, ionogel-based all-solid-state MSC is developed that showed performance comparable to liquid-state electrolyte with superior long-term cycling stability. This study gives a new perspective to develop all-solid-state micro-supercapacitors using pseudocapacitive active materials that can operate in ionic-liquid-based non-aqueous electrolytes compatible with on-chip IoT-based device applications seeking high areal energy/ power performance. References [1] N. A. Kyeremateng, T. Brousse, D. Pech, Nat Nanotechnol 2017, 12, 7. [2] C. Lethien, J. Le Bideau, T. Brousse, Energ Environ Sci 2019, 12, 96. [3] A. Ferris, D. Bourrier, S. Garbarino, D. Guay, D. Pech, Small 2019, 15, e1901224. [4] C. Zhong, Y. Deng, W. Hu, J. Qiao, L. Zhang, J. Zhang, Chem Soc Rev 2015, 44, 7484. [5] A. Ferris, S. Garbarino, D. Guay, D. Pech, Adv Mater 2015, 27, 6625. [6] M. Yoshizawa, W. Xu, C. A. Angell, J Am Chem Soc 2003, 125, 15411. [7] J. P. Belieres, C. A. Angell, J Phys Chem B 2007, 111, 4926. [8] D. Rochefort, A. L. Pont, Electrochem Commun 2006, 8, 1539.

3D porous electrodes have been considered as a new paradigm shift for increasing the energy storage of pseudocapacitive micro-supercapacitors for on-chip electronics. However, the conformal deposition of active materials is still challenging when highly porous structures are involved. In this work, we have investigated the atomic layer deposition (ALD) of ruthenium dioxide RuO2 on porous Au and Pt architectures prepared by hydrogen bubble templated electrodeposition, with area enlargement factors ranging from 400 to 10 000 cm(2)/cm(2). Using proper ALD conditions, a uniform RuO2 coverage has been successfully obtained on porous Au, with a specific electrode capacitance of 8.1 mF cm(-2) and a specific power of 160 mW cm(-2) for a minute amount of active material. This study also shows the importance of the chemical composition and reactivity of the porous substrate for achieving conformal deposition of a ruthenium oxide layer.

Data that supports the plots of Energy Storage Materials 47 (2022) 134–140

To power the next generation of miniaturized electronic devices, the energy storage capability of Li-ion micro-batteries has to be significantly improved and the fabrication of high performance 3D electrodes is mandatory. Here we show how to carefully match the design of efficient 3D scaffold based on metallic porous template with the deposition parameters of titanium dioxide films made from thermal Atomic Layer Deposition method for designing efficient 3D electrodes for Li-ion micro-batteries. A 3D electrode made from Pt porous scaffold coated with 150 nm-thick anatase TiO 2 film reaches a high surface capacity value up to 1600 μ Ah.cm −2 at C/12 with a good cycling stability during 100 cycles.

Small dimension Li-ion microbatteries are of great interest for embedded microsystems and on-chip electronics. However, the deposition of fully crystallized cathode thin film generally requires high temperature synthesis or annealing, incompatible with microfabrication processes of integrated Si devices. In this work, a low temperature deposition process of a porous Prussian blue-based cathode on Si wafers is reported. The active material is electrodeposited under aqueous conditions using a pulsed deposition protocol on a porous dendritic metallic current collector that ensures good electronic conductivity of the composite. The high voltage cathodes exhibit a huge areal capacity of ≈650 μAh cm-2 and are able to withstand more than 2000 cycles at 0.25 mA cm-2 rate. The application of these electrode composites with porous Sn based alloying anodes is also demonstrated for the first time in full cell configuration, with high areal energy of 3.1 J cm-2 and more than 95% reversible capacity. This outstanding performance can be attributed to uniform deposition of Prussian blue materials on conductive matrix, which maintains electronic conductivity while simultaneously providing mechanical integrity to the electrode. This finding opens new horizons in the monolithic integration of energy storage components compatible with the semiconductor industry for self-powered microsystems.

Three-dimensional (3D) electrodes with improved areal energy have become increasingly important for microscale energy storage at the dawn of the Internet of Things. At its heart are a plethora of microelectronic devices that require embedded energy harvesters and energy storage components to ensure autonomy. In this study, we develop porous metallic micro- structures and their conformal coating with a new RuOxNySz, material through a facile optimized electrodeposition process. The microporous structure with a nanodendritic network shows high areal capacitance (14.3 F cm(-2) for the electrode and 714 mF cm(-2) for an all-solid-state microsupercacitor) and stable perform- ance (>80% retention after 5000 cycles) toward storage. Remarkable Li+ storage capability with high areal capacity (5 mAh cm(-2)) and rate characteristics (1.5 mAh cm(-2) at 3C) is also observed. These results coupled with a facile synthetic strategy can thus offer inspiration for large-scale production of 3D porous electrodes for microbatteries and microsupercapacitors.

Hydrogen and its interaction with metal oxide surfaces is of major importance for a wide range of research and applied fields spanning from catalysis, energy storage, microelectronics, to metallurgy. This paper reviews state of the art of first principles calculations on the well-known ruthenium oxide (RuO2) surface in its (110) orientation and its interaction with hydrogen. In addition to it, the paper also fills gaps in knowledge with new calculations and results on the (001) surface. Bulk and surface interactions are thoroughly reviewed. This includes systematic analysis of adsorption sites, local agglomeration propensity of hydrogen, and migration pathways in which literature data and their potential deviations are explained. We notably discuss novel results on propensity for agglomeration of hydrogen within bulk channels [001] oriented in which the proton-like behavior of adsorbed hydrogen hinders further agglomeration in adjacent channels. The paper brings new insights into the migration pathways on the surface and in bulk, both exhibiting preferential diffusion paths along the [001] direction. The paper finally investigates the subsurface region. We show that while the subsurface has more stable sites for adsorption compared to bulk, its accessibility from the surface shows prohibitive activation barriers inhibiting penetration into subsurface and bulk. We further calculate and discuss adsorption and penetration processes on the alternative RuO2 (001) surface.

With its huge pseudocapacitance and excellent stability, ruthenium dioxide (RuO2) is considered to be one of the best electrode materials for supercapacitors. However, such properties are only obtained with hydrous RuO2 in an amorphous phase, limiting the range of possible deposition techniques. Herein we report a detailed understanding of reactions of protons (H+) occurring in crystalline RuO2 with regard to its orientation using density functional theory. In particular, we show that migration pathways are energetically favorable along the [001] direction, leading to a deeper H+ penetration within the bulk of the active material and a much higher charge storage ability.

Long-term stability is one of the most desired functionalities of energy storage microdevices for wearable electronics, wireless sensor networks and the upcoming Internet of Things. Although Li-ion microbatteries have become the dominant energy-storage technology for on-chip electronics, the extension of lifetime of these components remains a fundamental hurdle to overcome. Here, we develop an ultra-stable porous anode based on SnAu alloys able to withstand a high specific capacity exceeding 100 µAh cm −2 at 3 C rate for more than 6000 cycles of charge/discharge. Also, this new anode material exhibits low potential (0.2 V versus lithium) and one of the highest specific capacity ever reported at low C-rates (7.3 mAh cm −2 at 0.1 C). We show that the outstanding cyclability is the result of a combination of many factors, including limited volume expansion, as supported by density functional theory calculations. This finding opens new opportunities in design of long-lasting integrated energy storage for self-powered microsystems.

Hydrous RuOx has been one of the well-studied materials for application in supercapacitors owing to its excellent properties (high conductivity similar to metals, redox activity capable of fast faradaic reactions and structural water enabling swift proton transfer and decreased diffusion distance). The main issue regarding supercapacitors is that, they suffer from low energy density compared to batteries. One way to overcome this problem is to increase surface area of the active material and hence the energy stored through 3D structuration of current collector. Multiple techniques have been used in this regard like 3D printing, pholitography methods...etc. However, these techniques are pretty complex, time consuming and have constraining conditions. Hence, it’s necessary to develop economic and simple routes for 3D structuration of electrodes for micro-supercapacitors. One simple, time efficient and easy to set up method that can be used under ambient conditions is the electrochemical structuration using dynamic hydrogen bubble template (DHBT). With this strategy, 3D scaffolds which can hold small quantities of intrinsic pseudocapacitve materials like RuOx can be fabricated. The challenge in this latter case is magnified, needing controlled decoration of active materials for efficient utilization and full benefit of the 3D framework. Hence, the pursuit of superior micro-supercapacitors not only needs controlled deposition, but also requires stable 3D scaffolds to maximize capacitance per footprint area1. We have previously shown electrodeposition of active RuOx on porous gold electrodes for micro-supercapacitors achieving a capacitance of 3 F/cm².2 One other approach would be to deposit the active material directly by the DHBT method. As RuOx is a good conductor this would not hinder its efficiency (this would not be the case for MnO2 for example). The difficulty here is that, not all metals can be deposited by the DHBT technique as other factors play a crucial role such as the exchanged current density towards H2 evolution and mechanical stability3. In the current work, we report two different strategies for the 3D deposition of RuOx. The first is the successful fabrication of highly porous 3D platinum current collector using DHBT followed by a conformal coating of hydrous RuOx to achieve a specific capacitance as high as 7 F/cm². The second is the direct electrodeposition of the active material, RuOx, in a 3D porous structure. These two approaches are characterized and discussed within the framework of fabricating superior micro-supercapacitors with excellent capacitance and low internal resistance. References 1. N. A. Kyeremateng, T. Brousse, and D. Pech, Nat. Nanotechnol., 12, 7–15 (2017) 2. A. Ferris, S. Garbarino, D. Guay, and D. Pech, Adv. Mater., 27, 6625–6629 (2015) 3. Plowman, B. J., Jones, L. A., & Bhargava, S. K. Chem. Commun., 51, 4331–4346 (2015) Figure 1

This paper reports the synergetic effects of UV and visible light irradiation on the photocatalytic activity of well-defined nanostructures composed of TiO2 films and Au nanoparticles. New insights into the electronic as well as the chemical processes that drive water decomposition were obtained by varying the position of the NPs on top and at different depths inside the semiconductor film. This work highlights a synergetic effect of UV and visible light on the photocatalytic activity of all the Au containing structures: hydrogen produced under UV+Vis shows an 100 % enhancement compared to the net production obtained only under UV or vis light. The systems where Au NPs are embedded in the TiO2 outperform the one where NPs are positioned on the surface, indicating that water-splitting reaction occurs primarily on the TiO2 surface rather than on the metal. Photocurrent and photocatalytic activity measurements under UV (353–403 nm), visible (400– 1100 nm) and UV+Vis (300–1100 nm) light, revealed the synergetic contribution of UV and Vis. Indeed, the plasmonic Au NPs create an intense oscillating electric field at the Au NPs/semiconductor interface (visible light contribution); this mechanism coupled with the

Microscale energy storage for embedded electronics remains a major challenge at the dawn of the Internet of Things. In article number 1901224, David Pech, Daniel Guay, and co-workers describe the integration of 3D pseudocapacitive electrodes on a silicon wafer to realize all-solid-state interdigitated microsupercapacitors with a record cell capacitance of 812 mF cm−2 per footprint area.

Due to their high-power density and long lifetime, microsupercapacitors have been considered as an efficient energy supply/storage solution for the operation of small electronic devices. However, their fabrication remains confined to 2D thin-film microdevices with limited areal energy. In this study, the integration of all-solid-state 3D interdigitated microsupercapacitors on 4 in. silicon wafers with record energy density is demonstrated. The device electrodes are composed of a pseudocapacitive hydrated ruthenium dioxide RuO2 deposited onto highly porous current collectors. The encapsulated devices exhibit cell capacitance of 812 mF cm(-2) per footprint area at an energy density of 329 mJ cm(-2), which is the highest value ever reported for planar configuration. These components achieve one of the highest surface energy/power density trade-offs and address the issue of electrical energy storage of modern electronics.

Small-scale electrochemical capacitors, also called microsupercapacitors, have been the subject of intense research in the past few years as miniaturized energy storage components for modern electronics. Although numerous microfabrication processes have been successfully assessed to achieve low-profile supercapacitors with submillimeter-scale features, several advances still need to be made in their performance characteristics to become industrially viable components. Here we report the occurrence of unexpected properties of on-chip supercapacitors when reducing interelectrode spacing down to the nanometer scale. An ultrahigh power concomitant with a high capacitance and energy density, an unforeseeable extended cell voltage, and an impressive lifetime were obtained at such small dimensions with a focused ion beam (FIB) patterned nanosupercapacitor based on RuOx pseudocapacitive material. The scaling relationship between miniaturized supercapacitors and electrochemical responses leads to valuable understanding of electrode reactions and rate-limiting steps. This finding offers new opportunities in the design of integrated energy storage devices with improved properties.