(Photo)electrochemical transformations represent a promising route to convert waste into value-added chemicals and fuels. Among the various approaches, photoelectrochemical (PEC) CO₂ reduction is particularly attractive due to its potential for direct solar-to-chemical energy conversion. However, realizing such devices requires selective and stable multi-carbon (C₂⁺) product formation, which remains a key challenge in the field. In our recent work, we have focused on improving both the selectivity and stability of PEC systems by using novel photocathode materials and tailored interfaces.

Here, we explore the role of microenvironments in addressing reaction selectivity,1,2 and we couple this concept with integration of halide perovskite based photoelectrodes. We show that halide perovskite based photoelectrodes coupled with tailored catalytic interfaces enable enhanced CO₂ physisorption, leading to a substantial increase in ethylene production efficiency, while maintaining long-term stability.

We also propose a similar approach for the electrochemical nitrate (NO3−) reduction reaction (NO3RR), which is a promising route for NH3 production by utilizing NO3−, a ubiquitous pollutant commonly found in wastewater. The electrochemical NO3RR to NH3 is recognized as a tandem catalytic process, comprising two major steps: NO3− to NO2− and NO2− to NH3. Therefore, achieving high overall NH3 conversion efficiency requires effective catalysis in both steps. While many researchers have focused on developing novel electrocatalysts for NO3RR, the influence of the underlying microenvironment on selective NH3 production remains poorly understood. Herein, we investigate the use of organic modifiers, specifically ionomers, to enhance the electrochemical NO3RR to NH3 on pure Cu electrocatalysts, which inherently exhibit a large energy barrier for hydrogenation due to limited H* availability.

[1] A. K. Buckley, M. Lee, T. Cheng, R. V. Kazantsev, D. M. Larson, W. A. Goddard III, F. D. Toste, F. M. Toma, Electrocatalysis at Organic–Metal Interfaces: Identification of Structure–Reactivity Relationships for CO2 Reduction at Modified Cu Surfaces, JACS 2019, 141, 18, 7355–7364

[2] A. K. Buckley, T. Cheng, M. Hwan Oh, G. M. Su, J. Garrison, S. W. Utan, C. Zhu, F. D. Toste, W. A. Goddard III, Francesca M. Toma, Approaching 100% Selectivity at Low Potential on Ag for Electrochemical CO2 Reduction to CO Using a Surface Additive, ACS Catalysis 2021, 11, 15, 9034-9042

The photoelectrochemical (PEC) reduction of carbon dioxide (CO₂RR) offers a promising strategy for the reduction of greenhouse gas emissions through the generation of valuable chemical fuels. Herein we introduce a versatile 3D-printed photoelectrochemical reactor for CO₂ conversion, operating under continuous flow conditions. The modular and compact 3D-printed PEC flow reactor developed includes a back-illuminated Bismuth Vanadate (BiVO₄) photoanode decorated with an electrodeposited cobalt phosphide (CoP) cocatalyst, a proton-exchange membrane, and a Cu-coated GDE as cathode. The system is coupled in line with both a micro gas chromatograph (micro GC) and a benchtop NMR, enabling real-time analysis of gas and liquid products under operating conditions. The system achieves 4.34 mA cm⁻² for PEC water oxidation at 1.75 V, with areas of more than 1 cm². Integration with a stable copper nanoparticle-coated gas diffusion electrode (Cu/GDE) enabled the simultaneous water oxidation and CO₂ reduction, further increasing the photocurrent to 5.24 mA cm⁻² and effectively driving CO₂RR under continuous flow, demonstrating enhanced performance and operational stability over 100 hours, selectively producing acetate (C₂) and methanol (C₁) from CO₂, with a total Faradaic efficiency of almost 90%. Acetate production reached a maximum FE of 60%, under optimal operation conditions representing competitive performance in comparison to state-of-the-art systems. This work presents a scalable and efficient platform for sustainable fuel production via integrated PEC-EC conversion.

In the pursuit of sustainable global development, mitigating carbon emissions and addressing plastic waste accumulation have emerged as critical challenges. Solar-powered systems offer a clean, cost-effective pathway to tackle these issues by enabling the conversion of CO₂ into fuels while simultaneously recycling plastic waste into high-value products, advancing waste reduction and circular economy objectives.

The PHOENIX project embodies this dual approach, focusing on the stepwise, solar-driven conversion of CO₂, beginning with its reduction to carbon monoxide (CO) and subsequent transformation into propanol. Concurrently, PET plastic waste is upcycled into glycolic acid, establishing a synergistic system that integrates renewable fuel production with plastic waste valorization.

To realize this vision, PHOENIX advances a tandem solar system that couples a photovoltaic-electrolyzer (PV-EC) unit with a photoelectrochemical (PEC) cell capable of generating over 2 V under sunlight to drive the targeted electrochemical transformations efficiently. The system is also being evaluated under concentrated light conditions to enhance solar flux utilization, increasing reaction rates and device productivity.

Recent developments within the Leitat team have significantly advanced the PEC component of the PHOENIX system through the design of stable, scalable photoanodes based on hematite (α-Fe₂O₃), addressing two key challenges in PEC technology: operational stability under realistic solar flux and scalable fabrication for device-relevant areas.

The Leitat team has developed Ti- and Ge-doped hematite thin films,[1] which exhibit improved electrical conductivity and enhanced charge separation, reducing recombination losses and increasing photocurrent densities under simulated and concentrated solar illumination. To further enhance performance, these doped photoanodes have been decorated with robust Ni-based and NiPt@C co-catalyst, which significantly lower the overpotential for the oxygen evolution reaction (OER) while ensuring chemical stability in alkaline media. Moreover, the system enables the ethylene glycol oxidation reaction (EGOR), a key step for valorizing PET-derived ethylene glycol into glycolic acid, contributing to plastic waste upcycling under solar-driven conditions within the PEC module.

To address scalability, low-temperature deposition techniques compatible with large-area substrates have been implemented, enabling the production of photoanodes with active areas exceeding 25 cm² while maintaining uniform semiconductor and catalytic properties. These scalable photoanodes have demonstrated stable operation under continuous illumination, maintaining high photocurrent densities necessary for practical PEC operation in PHOENIX.

By integrating these advanced photoanodes within the PEC module, PHOENIX is positioned to demonstrate the solar-driven production of propanol from CO₂ while enabling the valorization of PET waste into glycolic acid within a unified, circular process. The system will undergo lab-scale validation at Technology Readiness Level (TRL) 4, including a Life Cycle Assessment (LCA) to evaluate environmental impact and material recyclability.

By addressing both CO₂ reduction and plastic waste recycling through innovative photoelectrode technology, PHOENIX represents a high-risk, high-reward approach poised to drive significant breakthroughs in renewable energy and waste management technologies.

Photoelectrochemical systems serve as prototype of artificial photosynthesis devices to produce sustainable fuels and chemicals from abundant and waste feedstocks. However, they are far from their practical utilization due to instability in aqueous environments and poor selectivity towards specific redox conversion reactions. The talk will focus on the main question, i.e., Do we have semiconductors that have intrinsic stability, and offer surface activity for PEC reactions?

I will introduce specific chalcogenide Cu(In,Ga)S₂ photocathodes that are interesting due to their bandgap tunability and defect-rich surface chemistry. Our results show that PEC CO₂R can be directly facilitated on bare CIGS surface producing CO and HCOO^- at Faradaic efficiency (FE) of 32 % and 14 % respectively, without any transport layer or co-catalyst. Mechanistic analyses and atomistic simulations reveal the role of surface composition to be critical for stability and activity towards CO₂R.[1] The aqueous stability and defect-rich surface of CIGS ensures adequate PEC activity towards nitrate (NO₃^-) to ammonia (NH₃) conversion. Our work highlights the discovery of a compositionally rich and stable system active for different redox reactions. The findings are useful to design highly stable and active photocathodes for driving photoelectrochemical reactions. I will finish my talk highlighting the opportunities and challenges ahead in realizing a standalone artificial leaf-like devices from emerging chalcogenide semiconductors.

We have designed, built and characterized a prototype photoelectrochemical demonstration system capable of splitting water into hydrogen and oxygen using only photon energies. The reactor was operated during Mar-May 2024 at Stellenbosch University (33.93° S, 18.86° E), while mounted on a 2-axis tracking platform. Light was directed laterally both into the (photo)cathode and photoanode compartments, which were separated by an ion-permeable membrane. Double-sided irradiation was achieved by two methods that were compared with each other: (i) using mirrors (Ag-coated mirror for the (photo)cathode side and Al-coated mirror for the photoanode side) and (ii) linear Fresnel lenses coupled with stepped Al waveguides. The latter irradiation method delivered light, concentrated by a factor of up to 4, though theoretical simulations show that through design improvement the concentration factor could ultimately reach ≈ 15.

The reactor was operated in two modes:

(a) Photoelectrochemical (PEC), utilising an FTO|WO₃|BiVO₄|NiFeO_x photoanode and a FTO|Au|Sb₂Se₃|CdS|TiO₂|Pt photocathode^[1,2];

(b) PV-assisted photoelectrochemical (PV-PEC), utilizing the same FTO|WO₃|BiVO₄|NiFeO_x photoanode, Ni cathode and an externally mounted c-Si PV.

In mode (a), a pH gradient was employed to assist water splitting, with a pH ≈ 0.8 aqueous catholyte comprising 0.1 M H₂SO₄ and anolyte comprising 1 M H₃BO₃ + 1 M NaOH at pH ≈ 9.3. In mode II, both electrolytes were 1 M H₃BO₃ + 1 M NaOH. A cation-permeable membrane, Nafion^TM 115, was utilized in all experiments. The reactor was operated in batch recycle mode. The areas of the (photo)electrodes and the PV were all 30 cm².

We observed that our bismuth vanadate (BVO) photoanodes usually degraded within hours, for which we propose two reasons. Firstly, when coupled with c-Si PV, the potential of the photoanodes was observed to increase into the dark current regions under low irradiance. While the c-Si PV is able to generate a significant photocurrent even on cloudy days, the bismuth vanadate photoanode is unable to match this through its own electron-hole generation. When anode potentials exceeded ≈1.1 V (RHE), the photoanode is thought to have degraded through oxidation of the bismuth; the degradation was irreversible. Secondly, the photoanodes degraded equally quickly under concentrated irradiance; we are currently investigating whether this was caused by overheating, high flux of bubbles or both. It is currently unclear whether the issue is with the adhesion of the WO₃ layer to FTO or due to the bismuth film itself, but this is under active investigation and we have partially aleviated the adhesion issue by introducing a planar WO₃ seed layer between the FTO and the WO₃ nanoneedles.

I shall discuss the experimental results from reactor testing, the performance under various modes of irradiation, and the effects of electrode materials, geometries and relative configurations within the  reactor on its design, overall performance and further scale-up, as well as the future role of photoelectrochemical systems in energy storage.

Oxygen evolution reaction (OER) is the rate limiting step in (photo)electrochemical solar fuels production processes in aqueous medium like water splitting or CO₂ reduction. This is because the oxidation of water is energetically demanding (1.23 V vs RHE at pH = 0 and 25 ^oC) and slow, with sluggish kinetics and a complex, multistep mechanism that involves 4 electrons. Noble metal oxides are typically employed as electrocatalysts, such as RuO_x or IrO₂, but these are scarce and expensive. [1] Therefore, cheaper, more accessible alternatives are required to escalate (photo)electrocatalytic solar fuels production. In this context, photoelectrocatalysts based on transition metal-oxides are thoroughly investigate due to their ability to harness sunlight to yield chemical reactions, their low cost and their accessibility.

Among them, bismuth vanadate (BiVO₄) stands out due to its: a) n-type character, b) narrow band gap (2.4 eV), c) suitable valence band (VB) position, d) non-toxicity, and e) low cost. However, this material also suffers from certain drawbacks, namely, slow carriers’ transportation and surface recombination that ultimately lead to slow OER kinetics and photocorrosion. [2]

Many approaches are being studied to tackle these inconveniences like different preparation methods, nanostructuring, heterojunctions, or usage of cocatalysts. In this work, we explore two of these strategies: i) inorganic-organic heterojunctions between BiVO₄ and a conjugated porous polymer (CPP) based on 1,3,5-tri(thiophen-2-yl)benzene (3TB) monomer; and ii) deposition of MOOH (M = Fe, Ni, Fe+Ni) cocatalysts over BiVO₄ films.

The BiVO₄ films were prepared over FTO substrates through electrodeposition followed by organometallic thermal decomposition. Then, a 3TB-based CPP was deposited with different thicknesses onto the BiVO₄ films by cyclic voltammetry (CV) and its presence was confirmed by energy-dispersive X-ray spectroscopy (EDX). The hybrid photoelectrodes were then characterized photoelectrochemically by linear sweep voltammetry (LSV) and chronoamperometry (CA) under chopped illumination. An enhancement in stability could be observed (Figure a).

In another set of BiVO₄ films, MOOH cocatalysts were deposited photo(electro)chemically on top of the films. The presence of the cocatalysts was confirmed by EDX and the morphology of the clusters was studied by field-emission sweep electronic microscopy (FE-SEM). Then, the devices were photoelectrochemically characterized by LSV under chopped illumination -where an improvement in photocurrent, fill factor, and photocurrent onset potential could be observed (Figure b)- and by electrochemical impedance spectroscopy (EIS) under dark and illumination conditions, that revealed a reduction in charge transfer resistance for all the cocatalyst-containing photoelectrodes.

Next steps will be focused on merging both strategies to build an FTO/BiVO₄/3TB/MOOH device, optimizing the preparation conditions, and characterize its properties.

Bismuth-based semiconductors, including the double perovskite Cs₂AgBiBr₆ but also perovskite-inspired materials such as bismuth oxyhalides or sulphides, show great promise for sustainable light-energy conversion due to their low toxicity, abundance, and tunable electronic properties. This presentation will explore strategies to enhance the efficiency, stability, and scalability of these materials in photoelectrocatalytic applications. Methods like automated film production, surface modifications, and heterojunction formation have been employed to improve the performance of BiOI and BiOBr in water splitting and hydrogen evolution reactions. A continuous automated film production method for BiOI and BiVO₄ photoelectrodes was introduced, significantly improving the reproducibility and efficiency of large-scale production. Surface modifications and heterojunction formation have been explored to optimize PEC performance, with enhanced water oxidation and hydrogen evolution reactions observed. Some recent hints on the use of hydrothermally synthesized, low bandgap and highly absorbing AgBiS₂ in PEC water oxidation will be further provided.  These advancements position bismuth-based semiconductors as viable, eco-friendly alternatives for energy conversion technologies.

Efficient conversion and storage of solar energy are crucial steps in the establishment of a renewable and carbon neutral energy supply. Photoelectrochemical (PEC) water splitting is a promising energy conversion and storage technology, considered very promising to make use of the large amounts of sunlight that reach the surface of earth. It renders the direct conversion of light into chemical energy possible, e.g. solar fuels like hydrogen or ammonia. By the aid of nanostructuring, diffusion pathways can be drastically shortened in case of low charge carrier diffusion lengths.

Due to its high electric conductivity, beneficial hole diffusion length, and band gap of 2.7 eV suitable to absorb visible light, WO₃ is a well-understood photoanode for photoelectrochemical water splitting.[1,2] In this contribution, a study to unravel the influence of seed layers on the performance of hydrothermally-grown WO₃ photonanodes will be presented.[3] Moreover, using a sol-gel synthesis method adapted from Hillard et al.,[4] we systematically investigated the influence of calcination temperature, film thickness, and porosity on the structural, optical, and electronic properties of WO₃ thin films, reaching photocurrent exceeding 3 mA cm^-2.

In recent years, earth-abundant Fe-based materials like spinel ferrites have emerged as auspicious materials for PEC. They have the inherent ability to absorb a large part of the visible light spectrum with band gaps around 2 eV, while some of them being also very good electrocatalysts. In this presentation, the activity and stability of both pristine and hydrogen-treated ZnFe₂O₄ will be presented.[5] Using an illuminated scanning flow cell setup, we monitored the activity and dissolution rates of ZnFe₂O₄ under operando PEC conditions. It was found that at PEC water oxidation conditions, ZnFe₂O₄ does not degrade in basic pH. Moreover, thermally reduced ZnFe₂O₄ shows expected higher OER activity without compromising the stability compared to the pristine one.

Bismuth vanadate (BiVO₄) is a promising photoactive material for oxidation reactions but is unstable in strongly acidic conditions, which remains a significant challenge, [1][2] particularly for applications like the glycerol oxidation reaction (GOR), [3] which has recently received high interest, since glycerol is a byproduct from the biodiesel industry and can be converted into high-value chemicals through selective oxidation and with a rather low energy input.

In this context, achieving stable photoanode performance at low pH conditions, is crucial for efficient and selective conversion of glycerol into high added-value products, like dihydroxyacetone (DHA), [4][5]. This communication will address our strategy to enhance the stability of BVO photoanodes in acidic solutions, by the deposition of nanometric layers of metal oxides (TiO₂, and Al₂O₃) through atomic layer deposition (ALD). Notably, BVO photoanodes modified with these protection layers demonstrate significantly improved stability, with negliglible loss of performance during at least 12 hours. This research demonstrates a viable strategy for improving the stability of BVO photoanodes in acidic environments, paving the way for more robust and efficient photoelectrochemical glycerol valorization.

Photoelectrochemical (PEC) water splitting using semiconductor photoelectrodes has emerged as a promising strategy for sustainable hydrogen production and solar energy storage. However, conventional semiconductor materials face critical limitations, such as rapid recombination of photogenerated electron-hole pairs and wide bandgaps, resulting in low solar-to-hydrogen conversion efficiencies. To address these issues, this study reports the synthesis and performance evaluation of microcapsule-structured α-Fe₂O₃ (hematite) photoanodes designed to enhance surface area and charge separation efficiency. Furthermore, the effect of doping with Ge or Si (X = Ge, Si) on the photoelectrochemical properties of α-Fe₂O₃ microcapsules (denoted as X-Fe₂O₃) was investigated, aiming to improve the charge transport and photocarrier separation behavior.

The α-Fe₂O₃ microcapsules (M-Fe₂O₃) were synthesized via a spray pyrolysis method using FeCl₃ aqueous solution. For the doped samples, Ge or Si precursors were added directly to the FeCl₃ solution prior to the spray pyrolysis process, yielding Ge-Fe₂O₃ and Si-Fe₂O₃ microcapsules. To fabricate the photoelectrodes, a seed layer of α-Fe₂O₃ was first prepared on fluorine-doped tin oxide (FTO) glass substrates by spin-coating a solution of FeCl₃ and Ti(OBu)₄ in ethanol, followed by thermal treatment. Subsequently, the synthesized Fe₂O₃ or metal doped Fe₂O₃ microcapsules were deposited onto the seed layer via electrophoretic deposition and then annealed to complete the electrode fabrication.

Electrochemical characterization was conducted in 1 M KOH aqueous solution using a standard three-electrode setup, where the fabricated photoelectrodes served as the working electrode, Pt as the counter electrode, and Ag/AgCl as the reference electrode. Linear sweep voltammetry (LSV) was performed under simulated sunlight irradiation (100 mW cm⁻²) using a xenon lamp. Material characterizations including scanning electron microscopy (SEM), X-ray diffraction (XRD), UV-Vis absorption spectroscopy, and X-ray photoelectron spectroscopy (XPS) were also conducted.

SEM observations revealed that the synthesized Fe₂O₃ particles exhibited a spherical microcapsule morphology with a diameter of approximately 1000 nm, which is advantageous for increasing the surface area and improving electrolyte contact. UV-Vis absorption spectra indicated that all photoelectrodes exhibited strong light absorption up to ~600 nm, consistent with the intrinsic absorption behavior of α-Fe₂O₃, and the estimated bandgap was approximately 2.09 eV. Notably, the metal doped-Fe₂O₃ electrodes showed enhanced absorption in the wavelength region above 550 nm, suggesting improved visible light harvesting due to the doping effect.

Photoelectrochemical performance data demonstrated that metal doped Fe₂O₃ electrodes exhibited higher photocurrent densities compared to undoped Fe₂O₃. Specifically, photocurrent onset was observed around 1.0 V_RHE for all electrodes, and at 1.23 V_RHE, the X-Fe₂O₃ photoelectrodes delivered a photocurrent density of 0.31 mA cm⁻², representing a ~1.1-fold improvement over the undoped Fe₂O₃ electrode. This enhancement is attributed to improved charge separation and transport facilitated by Ge or Si doping, which may act to reduce bulk recombination or modulate band structure favorably. In conclusion, the incorporation of Ge and Si dopants into microcapsule-type α-Fe₂O₃ electrodes successfully enhanced PEC performance by improving light absorption and promoting charge carrier separation. Further improvements are expected by modifying the electrode surface, for example, through the electrodeposition of cobalt phosphate (Co-Pi), which may further suppress surface recombination and boost overall water-splitting efficiency.

Photocatalysis and photoelectrochemical cells (PECs) have been developed as environmentally friendly systems that can directly utilize photogenerated electron-hole pairs for water splitting, fuel production, conversion of carbon dioxide, and pollutant degradation. Most reports on the photocatalytic or PEC hydrogen (H₂) evolution via water splitting have focused on the H₂ reduction half-reaction by generating the photoanode non-valuable oxygen or using sacrificial agents to consume the generated h⁺, resulting in a significant waste of energy. Lately, much effort has been invested into synthesizing valuable chemicals on the photoanode while retaining the production of H₂ on the cathode. Over the past few years, polymeric carbon nitrides (CN) have attracted widespread attention due to their outstanding electronic properties, which have been exploited in various applications, including photo- and electro-catalysis, heterogeneous catalysis, CO₂ reduction, water splitting, light-emitting diodes, and PV cells. CN comprises only carbon and nitrogen, and it can be synthesized by several routes. Its unique and tunable optical, chemical, and catalytic properties, alongside its low price and remarkably high stability to oxidation (up to 500 °C), make it a very attractive material for photoelectrochemical applications. However, only a few reports regarded CN utilization in PECs due to the difficulty in acquiring a homogenous CN layer on a conductive substrate and our lack of basic understanding of the intrinsic layer properties of CN. This talk will introduce new approaches to growing CN layers with altered properties on conductive substrates for photoelectrochemical applications. The growth mechanism and their chemical, photophysical, electronic, and charge transfer properties will be discussed. The utilization of PEC with a CN-based photoanode as a stable and efficient platform for oxidizing organic molecules to added-value chemicals, with hydrogen co-production, will be presented.

Perovskite and organic photoactive materials, owing to their exceptional optoelectronic properties, are regarded as highly promising candidates for integration into photoelectrochemical systems aimed at green hydrogen generation via solar water splitting. These photoactive material classes have attracted substantial research interest, having achieved record-high power conversion efficiencies in single-junction photovoltaic devices. Nonetheless, their application in photoelectrodes remains constrained by intrinsic instability under aqueous conditions.

A cost-effective encapsulation methodology for halide perovskite and organic photoactive layers will be presented, which enabled both prolonged operational stability (>100 hours) and high photocurrent densities for water oxidation (>8 mA cm^‑2 and >25 mA cm^‑2 at 1.23 V_RHE, respectively).^1–3 Furthermore, monolithic organic tandem photoanodes will be shown to exhibit exceptionally low (negative) onset potentials, facilitating bias-free water splitting in a two-electrode configuration with solar-to-hydrogen (STH) efficiencies exceeding 5%³, alongside improved operational stability under full-spectrum solar irradiation.

In solar water splitting, significant energy loss arises due to the high overpotential associated with the oxygen evolution reaction, which results in the production of a low-value product: oxygen. Our recent efforts have focused on coupling perovskite-based photoelectrodes with alternative oxidation reactions to enhance system efficiency and product value. Our findings will be presented on the use of perovskite photoelectrodes for simultaneous hydrogen generation and the oxidation of glycerol to value-added products. By employing absorber materials with optimized optical bandgaps (~1.6 eV) in conjunction with a Au–Pt–Bi electrocatalyst, bias-free operation was achieved, yielding photocurrent densities exceeding 10 mA cm⁻² and operational stability beyond one hour. Necessary steps to achieve longer stability and increased product selectivity will be also discussed.

Nanomaterials can offer unique properties due to their high surface-to-volume ratio which can be carefully tailored as a function of the selected synthetic approach and thus making them highly attractive in various applicative fields including catalysis, sensing, and remediation. In this context, a lot of efforts have been devoted to the development of sustainable solutions aimed both at reducing the dependence on fossil fuels and the concomitant depollution actions in various environments. This contribution will report on our recent research group achievements toward the design of active catalysts for environmental applications, including photoelectrochemical water splitting processes and the degradation of water pollutants. To this purpose, among the possible candidates, we focus our attention on the carbon nitride (g-CN) based composite nanomaterials prepared by hybrid fabrication routes which allow a precise control over chemical composition, size, and properties, resulting in complex structures endowed with unique characteristics. This lecture will focus on the following selected case studies: a) Pt-gCN nanocomposite architectures, prepared by electrophoretic deposition and RF-sputtering, highlighting attractive EOR performances with minimal platinum content [1]; b) Cu_xO-functionalized carbon rich g-CN based deposits obtained through an original multi-step plasma-assisted approach consisted in the coupling of magnetron sputtering and (RF)-sputtering, showing appealing OER electrocatalytic activity [2]; c) gCN based photocathodes was developed for the efficient generation of H₂O₂ to promote electro-Fenton processes for the degradation of fenitrothion (FNT), a widely used organophosphate pesticide [3].

Selective oxidation of biomass-derived molecules such as glycerol at the photoanode offers a compelling strategy to enhance the efficiency and value proposition of photoelectrochemical (PEC) systems [1]. In this talk, we will present our recent work on the PEC oxidation of glycerol over nanoporous BiVO4 photoanodes, which exhibit intrinsic activity without the need for co-catalysts [2, 3]. Focusing on electrolyte engineering, we demonstrate how specific anion and cation effects—interpreted through the Hofmeister series—modulate interfacial charge transfer, photocurrent response, product selectivity, and long-term stability [3]. Among various electrolytes, NaNO₃ yields the highest selectivity (~50%) toward glycolaldehyde and overall PEC performance [3], highlighting the critical role of electrolyte composition in driving complex multielectron oxidation reactions.

To complement these experimental insights, we will discuss our thermodynamic analysis of glycerol oxidation under PEC-relevant conditions [4]. Our calculations reveal how applied bias and temperature influence product distributions, energy efficiency, and reaction spontaneity [4], providing a framework for interpreting experimental trends and guiding future materials and device optimization.

Lastly, we will introduce a modular, side-by-side design for a membraneless PEC device enabling simultaneous solar-driven glycerol oxidation and hydrogen production [5]. By addressing crossover and stability challenges via flow dynamics and electrolyte symmetry, we demonstrate a scalable approach to solar-driven biomass reforming. These results underline the synergy between materials design, electrolyte selection, and device architecture in advancing PEC systems for sustainable fuel and chemical production.

Photoelectrochemistry (PEC) presents a direct pathway to solar fuel synthesis by integrating light absorption and catalysis into compact electrodes.^[1-3] Among established light absorbers, metal halide perovskites have emerged as promising alternatives for solar fuel synthesis, enabling unassisted water splitting^[4,5] and CO₂ reduction to syngas.^[6-9] Yet, PEC hydrocarbon production remains elusive due to high catalytic overpotentials and insufficient semiconductor photovoltage. Here we demonstrate ethane and ethylene synthesis by interfacing lead halide perovskite photoabsorbers with suitable copper nanoflower electrocatalysts.^[10] The resulting perovskite photocathodes attain a 9.8% Faradaic yield towards C₂ hydrocarbon production at 0 V against the reversible hydrogen electrode. The catalyst and perovskite geometric surface areas strongly influence C₂ photocathode selectivity, which indicates a role of local current density in product distribution. The thermodynamic limitations of water oxidation are overcome by coupling the photocathodes to Si nanowire photoanodes for glycerol oxidation into value-added chemicals like glycerate, lactate, acetate and formate. These unassisted perovskite–silicon PEC devices attain partial C₂ hydrocarbon photocurrent densities of 155 µA cm⁻², 200-fold higher than conventional perovskite–BiVO₄ artificial leaves for water and CO₂ splitting. These insights establish perovskite semiconductors as a versatile platform towards PEC multicarbon synthesis.^[10]