Solar plastic upcycling is demonstrated through the photoelectrochemical oxidation of ethylene glycol derived from real world, pretreated polyethylene terephthalate (PET) bottle waste on an n-Si/Ni photoanode, producing formic acid and glycolic acid with high Faradaic efficiency. The catalytic silicon photoanode promotes efficient interfacial charge transfer under simulated solar illumination in alkaline media, enabling selective oxidation of PET-derived ethylene glycol. Mechanistic insights obtained from electrochemical and spectroscopic analyses indicate that nickel oxyhydroxide species facilitate C─C bond cleavage through surface-bound intermediates. These findings highlight the potential of silicon-based photoanodes as promising platforms for solar-driven plastic waste valorization and sustainable carbon recycling.

Electrochemiluminescence (ECL) triggered by bipolar electrochemistry (BE) allows combining wireless electrochemical addressing with a simple optical readout, which enables effective analytical applications. A key factor in BE-ECL is the spatial distribution of the ECL-emitting region(s), which depends on the local electric field and the type and shape of the bipolar electrode (BPE). In this work, spatially resolved ECL emission, originating from single or interconnected beads acting as building blocks for BPE arrays was investigated. The impact of the spatial and compositional anisotropy within the BPE array was imaged by the ECL response of the model [Ru(bpy)3]2+/tri-n-propylamine system. This approach allows the design of a versatile and straightforward platform for high-throughput screening and real-time visualization of electrochemical activity within a single BPE with tuneable composition and chemical reactivity. Furthermore, this work may open up new perspectives for multiplexed biosensing of analytes and screening tools with encoded signals in anisotropic electrode arrays.

Water splitting is one of the most efficient approaches to clean hydrogen production. Assessing electrolyzer performance requires evaluating the efficiency of electrocatalysts. Herein, a motion‐based method is presented that combines bipolar electrochemistry (BE) with dynamic, chemically induced electromagnets to probe the electrocatalytic efficiency of water splitting. With this approach, redox reactions are triggered in a wireless way at both extremities of a solenoid‐shaped electrolyzer composed by different metal catalysts. The resulting current follows the helical coil, producing a concentrated magnetic field that drives rotational motion in the presence of an external magnetic field without traditional ferromagnetic materials. A direct correlation between the angular velocity and the catalyst efficiency is obtained. Furthermore, by applying an alternating electric field, the resulting device behaves as a direction‐sensitive dynamic electrolyzer, with its angular velocity determined by which catalyst serves as the anode or cathode, respectively. This strategy provides a simple, wireless readout for catalyst screening, offering a new tool for hydrogen generation research.

Although it is known that iron (Fe) significantly alters the electrocatalytic activity of nickel (Ni)-based materials, little attention has been paid to the effects of Fe impurities on the photoelectrochemical (PEC) properties of solar-driven water-splitting photoanodes. Herein, we elucidate the crucial role of Fe in model metal-insulator-semiconductor (MIS) Si photoanodes decorated with Ni nanoparticles (NPs), known for their high performance in photoinduced water splitting. Our results demonstrate that residual Fe strongly influences the photoanodes' junction energetics and photovoltaic properties. We show that the synergistic effects (electrocatalytic/photovoltaic) caused by Fe doping explain the high performance previously reported for these model photoanodes. Crucially, Fe incorporation into the outer shell of Ni NPs and the electrolyte is essential to achieve the reported photovoltage up to 500 mV. Our investigations emphasize the importance of Fe in PEC devices, which has always been neglected in the past.

Metal-insulator-semiconductor (MIS) photoanodes are increasingly employed for solar water splitting due to their high performance. Here, we introduce a photoelectrochemical (PEC) mapping system that utilizes the scanning light beam of a confocal microscope, focused onto the surface of a photoanode. This approach enables submicrometric spatial resolution, which we employ to study photocurrent generation in MIS photoanodes constructed from n-type Si (n-Si) coated with oxygen evolution reaction (OER)-active Ni micropatterns. Our study highlights several key features. First, minority carrier (hole) transport beneath the uncoated SiO x surface is influenced by the presence of electrolyte at the interface. Second, the main photocurrent contribution arises from illumination of Ni-free regions, even mm away from the Ni active sites. Third, the hole collection at the catalyst becomes significantly limited under high-intensity illumination regimes. These results are rationalized, allowing a general description of the transport of photogenerated holes in these MIS photoanodes. Furthermore, PEC mapping directly reveals that the issue of limited hole collection at high illumination intensities can be mitigated by shortening the spacing between catalyst islands. These findings offer key insights for designing more efficient PEC-based solar fuel systems that perform efficiently under high light intensities, such as concentrated sunlight.

Carbon nitride (CN) is a highly promising electrochemiluminescence (ECL) nanomaterial operating in aqueous media at physiological pH. Here, we report the upconversion photoinduced ECL (PECL) emission on a p-type Si modified with CN nanosheet (p-Si/CNNS) photocathode in aqueous solution. The PECL activity of the single micrometer-sized CNNS was directly imaged by microscopy, revealing the heterogeneity at the single-particle level. In addition, the reported approach allows decreasing the onset ECL potential to -0.47 V vs. Ag/AgCl. This study opens new avenues for light-addressable electrochemical systems, the optimization of CNNS reactivity, and the study of new ECL materials.

Redox cycling (RC) is often used to amplify the faradaic current associated with the electrochemical transformation of redox-active species. For a given concentration, this allows a considerable increase in sensitivity and an improvement in the detection limit of analytical devices. However, all previous reports have focused only on the detection of achiral molecules, e.g., ferrocene derivatives. In this contribution, we report an original setup composed of two metal electrodes encoded with chiral features, facing each other to form a microchannel. The presence of the same chiral feature on the two parallel-oriented electrodes enables the preferential cyclic transformation of a specific enantiomer. It will be more easily oxidized at the anode with the right chirality and can subsequently diffuse across the microchannel to be reduced back into the starting enantiomer at a cathode with an identical chiral feature. As a function of the width of the microchannel, this cycle is repeated multiple times, significantly enhancing the overall current in terms of chiral recognition. Herein, we illustrate this fundamental concept with mesoporous Pt-Ir alloy electrodes, imprinted with either L-DOPA or D-DOPA as transducers constituting the microchannel. The latter allows an amplification of the analytical signal of DOPA as a model compound by more than one order of magnitude and with an enantiodiscrimination efficiency reaching 90%. Thus, the proposed strategy opens up very interesting perspectives for chiral-sensing applications.

Tip-enhanced Raman spectroscopy (TERS) is a powerful technique for nanoscale chemical imaging. However, its worldwide expansion is still limited by the challenging fabrication of cheap, robust and efficient TERS tips as optical nanosources to amplify the Raman signal. An original method based on bipolar electrodeposition is described here to prepare gold-coated AFM cantilevers used as TERS tips. This wireless method is simple to implement, cost-effective, and allows for the parallel fabrication of several TERS tips with good reproducibility of the metal thickness and a relatively long lifetime. The TERS activity was confirmed by imaging graphene oxide flakes with high spatial resolution (below 10 nm). A promising yield of 64% was achieved for the fabrication of active TERS tips. Therefore, this method could pave the way for the development of new chemical routes for the preparation of TERS tips and other plasmonic nanostructures.

Oil-in-water Pickering emulsions can be stabilized by poly-N-Isopropylacrylamide based microgels that adsorb, deform and entangle at the droplets interface. The surface coverage Γemulsion, defined as the mass of microgels per unit interfacial area, likely plays a key role in the emulsion properties as stability and responsiveness. The objective of the present study is to link Γemulsion to the concentration of microgels used during the emulsification process. Γemulsion was monitored by combining droplet size analysis, UV-visible quantification of non-adsorbed microgels and Cryo-SEM visualization of the droplets interface, for a microgel concentration range over almost two decades. We demonstrate the existence of three regimes. At low microgel concentration, in the particle-poor regime, the well-known "Limited Coalescence" process takes place. All the microgels adsorb, the droplet size distribution is narrow and the mean droplet size is inversely proportional to the microgel concentration: a constant minimum value of Γemulsion characterizes this domain. For higher microgel concentrations, microgels partition between the interface and the bulk continuous phase. In this intermediate "Excess" regime, both adsorbed and non-adsorbed microgel increase, proving that microgels compress at the interface to maximize their adsorption. At higher microgel concentrations, a third regime named "Saturation" regime is observed for the first time. Γemulsion then reaches a constant high plateau value while the drop size distribution becomes polydisperse, showing that the fragmentation process dominates over the coalescence. These findings should open new perspectives to better tailor emulsion properties using deformable particles as stabilizers.

HYPOTHESIS:Poly(N-isopropylacrylamide) (pNIPAM) microgels are soft particles that adsorb at liquid interfaces and confer emulsion stability against coalescence. Their conformation and interactions at the interface greatly impact the mechanical properties of the interface. In particular, the interfacial elastic modulus increases as the microgel cross-linking density decreases, as a consequence of microgel ability to deform and entangle with neighbors. The purpose of this work is to investigate how these features can be tuned by physical interactions between superchaotropic Keggin nano-ions (POMs) and pNIPAM microgels. EXPERIMENTS:Interactions between polyoxometalates (POMs) and pNIPAM microgels of varying cross-linking densities and sizes are investigated in aqueous suspensions and at liquid/liquid interfaces. The ability of microgels to stabilize oil-in-water emulsions is assessed by evaluating their kinetic stability and flow characteristics, with POMs introduced either before or after emulsification. Cryogenic electron microscopy (cryo-EM) is employed to directly visualize the microgel-stabilized emulsions. The adsorption of microgels, at a model interface and the resulting interfacial elasticity with various POM concentrations, are also studied using the oscillating pendant drop method. FINDINGS:POMs act as physical cross-linkers that promotes microgel deswelling. For large microgels, this effect increases their stiffness. and thus adding POMs reduces the stability of the emulsions. In contrast, small POM-loaded microgels produce highly stable emulsions that resist coalescence under mechanical stress or temperature increase. The same is true for large microgels supplemented in POMs after emulsification. Indeed, POMs enhance interfacial elasticity by promoting both intra-particle and inter-particle crosslinking at the interface. Lastly, by connecting microgel monolayers between neighboring droplet surfaces, POMs promote adhesion between droplets. All levels of the multiscale structure within Pickering emulsions are controlled by interactions between POMs and pNIPAM.

Green hydrogen (H2) can play a pivotal role in reducing global carbon emissions. This renewable fuel can be produced by water-splitting photoelectrochemical (PEC) devices that require a photoanode and a photocathode to serve as solar light absorbers and energy converters. So far, the use of III-V semiconductor materials as photoelectrodes has resulted in the best performance for PEC water splitting. However, the cost of these materials still prohibits their spread. Instead of employing bulk III-V wafers as photoelectrode substrates, using III-V thin film layers on inexpensive substrates to manufacture photoelectrodes appears to be, thus, a promising solution to solve this problem. Herein, we present the preparation and the study of photocathodes consisting of a thin film of GaAs grown by molecular beam epitaxy (MBE) on a p-doped Si (Si:p) substrate, which are subsequently modified by photoelectrodeposition of Ni catalyst. These Ni/GaAs/Si:p photocathodes are used for the solar-driven H2 evolution reaction (HER) in alkaline medium. We show that these photocathodes are stable in operation for several hours under illumination with a 100% Faradaic efficiency for H2. This constitutes the first example of the use of Ni as a catalyst on GaAs photocathodes. While these results support the fact that MBE-grown III-V thin films can afford HER in alkaline media when modified with an inexpensive catalyst, the effect of the GaAs thickness on incident-photon-to-electron conversion efficiency (IPCE) data shows that the III-V layer hinders the overall HER activity of the photoelectrode. Therefore, further material engineering strategies are required to improve the HER performance of these promising photocathodes.

Si photoanodes decorated with Ni nanoparticles (NPs) are known for their high performance in photoelectrochemical (PEC) solar water splitting and have been considered model systems for the mechanistic study of inhomogeneous metal-insulator-semiconductor (MIS) photoanodes. However, little attention has been paid to the effects of Fe impurities on the PEC properties despite Fe being recognized to significantly alter the electrocatalytic activity of Ni-based materials. Herein, we elucidate the crucial role of Fe in MIS photoanodes for water oxidation under light. Our results demonstrate that not only does the presence of residual Fe affect the electrocatalytic properties but also strongly influences the photoanodes’ junction energetics and photovoltaic properties. We show that the synergistic effects caused by Fe doping explain the high performance previously reported for these model photoanodes. The correlation between photovoltage, Fe content, and Ni NP size is rationalized by the pinch-off effect and the change in the effective barrier height of Ni(OH)2/NiOOH shell upon Fe incorporation. To achieve a high photovoltage (up to 500 mV), Fe incorporation into the outer shell of Ni NPs and the electrolyte is essential. Our results emphasize the importance of Fe in this PEC system, which has always been neglected in the past. These results are essential for the fundamental understanding of water-splitting photoelectrodes and will help improve the performance assessment of systems for converting solar energy into hydrogen.

Externally driven chemo-electromagnets were designed by coupling bipolar electrochemistry and the geometry of a solenoid. The chemically induced magnetic dipole allows control of the dynamic displacement, without the use of ferromagnetic materials.

Semiconductor (SC)-based photoelectrodes, employed for the production of solar fuels, such as H2 or small organic molecules, have garnered significant attention and extensive studies because they could play a crucial role in addressing the global energy crisis. While macroscopic photoelectrochemical (PEC) studies of these systems are routinely employed to monitor the overall activity of these systems, the spatiotemporal resolution of local PEC activity down to the nanoscale remains a challenge, which could lead to considerable improvement in photoelectrode design and engineering. Here, model Si-based photoanodes precisely coated with water-splitting Ni catalysts of various sizes are studied by photoinduced electrochemiluminescence (PECL) microscopy. Our results demonstrate that this method allows precise imaging of hole-driven photoelectrochemical reactivity down to a scale of similar to 50 nm, making PECL microscopy a valuable tool for elucidating charge transfer and local interfacial activity of photoelectrodes employed in PEC solar energy conversion processes.

Glassy carbon electrodes were modified with a CeO2 film and Pt nanoparticles (Pt-CeO2) for electrocatalysis. Interestingly, the oxidation of benzyl alcohol was significantly enhanced when Pt-CeO2 films were prepared by the simultaneous electrodeposition of the two materials, indicating a significant synergistic electrocatalytic activity. Subsequently, bipolar electrochemistry was employed to prepare Pt-CeO2 gradient films. Scanning electrochemical microscopy (SECM) was employed for studying local electrochemical properties at liquid/solid interfaces. SECM allowed mapping the local electrochemical performance of the Pt-CeO2 gradient films for benzyl alcohol oxidation, showing that the reaction rate is proportional to the local Pt-CeO2 surface coverage. Therefore, Pt-CeO2 deposits with different densities along the bipolar electrode offer tunable catalytic performances for benzyl alcohol oxidation. This allows identifying in a fast and straightforward way the optimal conditions for electrocatalytic processes in a more general sense because the approach, illustrated here with one specific reaction, can be easily generalized to other catalytically-active surfaces.

An electromagnet is a particular device that takes advantage of electrical currents to produce concentrated magnetic fields. The most well-known example is a conventional solenoid, having the form of an elongated coil and creating a strong magnetic field through its center when it is connected to a current source. Spontaneous redox reactions located at opposite ends of an anisotropic Janus swimmer can effectively mimic a standard power source, due to their ability to wirelessly generate a local electric current. Herein, we propose the coupling of thermodynamically spontaneous redox reactions occurring at the extremities of a hybrid Mg/Pt Janus swimmer with a solenoidal geometry to generate significant magnetic fields. These chemically driven electromagnets spontaneously transform the redox-induced electric current into a magnetic field with a strength in the range of μT upon contact with an acidic medium. Such on-board magnetization allows them to perform compass-like rotational motion and magnetotactic displacement in the presence of external magnetic field gradients, without the need of using ferromagnetic materials for the swimmer design. The torque force experienced by the swimmer is proportional to the internal redox current, and by varying the composition of the solution, it is possible to fine-tune its angular velocity.

Chemistry on-the-fly is an interesting concept, extensively studied in recent years due to its potential use for recognition, quantification and conversion of chemical species in solution. In this context, chemistry on-the-fly for asymmetric synthesis is a promising field of investigation, since it can help to overcome mass transport limitations, present for example in conventional organic electrosynthesis. Herein, the synergy between a magnetic field-enhanced self-electrophoretic propulsion mechanism and enantioselective redox chemistry on-the-fly is proposed as an efficient method to boost stereoselective conversion. We employ Janus swimmers as redox-active elements, exhibiting a well-controlled clockwise or anticlockwise motion with a speed that can be increased by one order of magnitude in the presence of an external magnetic field. While moving, these bifunctional objects convert spontaneously on-the-fly a prochiral molecule into a specific enantiomer with high enantiomeric excess. The magnetic field-enhanced self-mixing of the swimmers, based on the formation of local magnetohydrodynamic vortices, leads to a significant improvement of the reaction yield and the conversion rate.