Solar panels are well established to produce electricity as photovoltaic cells and are already in development to photo-catalyse overall water splitting to produce green hydrogen as artificial leaves or photocatalyst sheets.^1,2 This presentation will introduce solar chemistry panels as an emerging technology to enable sunlight-powered circular carbon chemistry. Our progress in designing and constructing prototype solar devices for the direct conversion of carbon dioxide as well as the valorisation of biomass and plastic waste streams into renewable fuels and higher-value chemicals will be presented. 

Specifically, a standalone artificial leaf based on an integrated lead halide perovskite-BiVO₄ tandem light absorber architecture with immobilised molecular catalysts has been created for solar CO₂ reduction to produce syngas (CO and H₂) fuel coupled to oxygen (O₂) evolution from water oxidation.³ Further manufacturing advances have enabled the reduction of material requirements to fabricate light weight devices that float on water, thereby enabling applications on open water sources instead of requiring land for installation.⁴ The versatile tandem design also allows for the integration of biocatalysts and thus the assembly of semi-artificial photosynthetic devices, demonstrating selective and bias-free conversion of CO₂-to-formate using immobilised enzymes.⁵ Recent progress in catalyst-development has allowed us to show carbon-carbon bond formation and the direct production of ethanol and propanol directly from CO₂, establishing artificial photosynthesis to produce liquid multicarbon fuels.⁶ The encapsulated perovskite photoelectrodes also provide a platform for the assembly of wireless solar devices for the valorisation of biomass and plastic waste through solar reforming (instead of oxidising water), ^7,8 as well as the coupling to CO₂-to-fuel conversion,⁸ including atmospheric CO₂ through integrated direct air capture.⁹ 

An alternative solar carbon capture and utilisation technology is based on co-deposited semiconductor powders on a conducting substrate.² Modification of these immobilised powders with a molecular catalyst provides us with a photocatalyst sheet that can cleanly produce formate from aqueous CO₂ while co-producing O₂.¹⁰ CO₂-fixing bacteria grown on such tandem photocatalyst sheets enable the production of multicarbon products through clean CO2-to-acetate conversion.¹¹ The deposition of a single semiconductor material on glass allows sunlight-driven plastic and biomass waste upcycling to organic products coupled to hydrogen evolution or CO₂-to-fuel conversion, thereby allowing for simultaneous waste remediation and fuel production.^12,13  

The concept and prospect of integrated solar chemistry panels for artificial photosynthesis and solar reforming,^14,15 strategies to improve light management in such devices¹⁶ and their relevance to secure and harness sustainable energy supplies in a circular economy will be discussed.

Perovskite and organic photoactive materials due to their excellent optoelectronic properties have great potential to be used in photoelectrochemical devices for green hydrogen generation via solar water splitting. These two types of materials have attracted great scientific interest by reaching record high single-junction solar cell efficiencies, but their photoelectrode performance is currently limited by their instability in an aqueous environment.

We will present a cost-effective way of protecting halide perovskite and organic photoactive layers used to reach both stable (>100 hours) and remarkably high, water oxidation photocurrents (>8 mA cm^‑2 and >25 mA cm^‑2 at 1.23 V_RHE, respectively).[1-3] We will also show monolithic organic tandem photoanodes with exceptionally low, negative onset potential and bias-free water splitting in two-electrode setup with solar-to-hydrogen efficiency reaching up to 5%. [3]

However, in solar water-splitting, due to the high overpotential of water oxidation a significant amount of energy is lost producing a low market value product (oxygen). In this presentation, we will show our most recent results on how we can apply graphite sheet protected organic and perovskite photoelectrodes to achieve simultaneous production of solar hydrogen and a value-added product from glycerol. We will show that the carefully chosen energetics of the perovskite and organic photoactive materials (optical bandgaps of 1.6 and 1.5 eV, respectively) combined with a developed Au–Pt–Bi electrocatalyst allows us to reach both bias-free operation and photocurrents close to the theoretical limit of the materials.

The sluggish kinetic of oxygen evolution reaction (OER) consistently reduces the efficiency of solar water splitting and therefore its competition with the fossil-based technologies widely available on the market. To overcome this limitation, the focus of the scientific community is shifting towards alternative oxidation reactions¹, characterized by lower energy requirements and inexpensive starting compounds. In this work, the oxidation of biomass derivatives into useful chemicals was investigated at the anodic compartment of a photoelectrochemical (PEC) cell. The photoanode was selected, evaluating the material’s stability, performance, and sustainability, in addition to the specific selectivity towards the desired products. The following PEC systems were explored:  i) Titanium doped hematite (Ti: Fe₂O₃) photoanodes, modified with cobalt- or nickel-based co-catalysts, for the conversion of 5-hydroxymethil furfural (HMF) into 2,5- furan dicarboxylic acid (FDCA); ii) bismuth vanadate (BiVO₄) photoanodes for glycerol oxidation to dihydroxyacetone (DHA).

Ti: Fe₂O₃ photoanodes were employed to oxidize the biomass derivative HMF to FDCA, a valuable building-block chemical for the synthesis of the PET-alternative, polyethylene furanoate (PEF). At first, a borate buffer solution was employed (pH 9) and the (2,2,6,6-Tetramethylpiperidin-1-yl) oxyl (TEMPO) mediator was introduced to accelerate the process. To improve selectivity over OER, cobalt-based cocatalysts were deposited on the photoanode’s surface, and the one modified with cobalt phosphate (CoPi) showed the highest efficiency and selectivity for FDCA². The source of this enhancement was correlated to the effect of the cocatalyst on the charge carrier dynamics, investigated by electrochemical impedance spectroscopy (EIS) and Intensity Modulated Photocurrent Spectroscopy (IMPS). To avoid the use of TEMPO, nickel-based electrocatalysts were deposited on the electrode’s surface. The Ni(OH)₂-electrodeposited (Ti: Fe₂O₃-Ni)³ and the NiMo-sputtered Ti: Fe₂O₃ photoanodes (Ti: Fe₂O₃-NiMo) were tested for the direct HMF oxidation in 0.1 M NaOH (pH 13) electrolyte. Partial HMF photoelectrochemical conversion to FDCA was achieved, pointing out the beneficial effect of Ni-based co-catalyst in shifting the selectivity. Operando X-ray Absorption Spectroscopy (XAS) measurements were also performed to explore the interaction between HMF and the two deposited electrocatalysts, helping to achieve some insights into the oxidation mechanism.

Glycerol oxidation to DHA was studied using nanoporous BiVO₄ photoanodes under acidic conditions, in a flow PEC cell. This time, no cocatalysts nor electron mediator were required, as glycerol proved to be an effective hole scavenger for this photoanode. The stability of the semiconductor was evaluated through long-term chronopotentiometries, both by fixing and modulating the current over time. After the conversion, a photoelectrochemical characterization was performed to assess the photoanode’s performance and SEM images were acquired for structural analysis.

Overall, a deep understanding of the favourable reaction conditions was essential not only to enhance process efficiency, but also to elucidate the underlying oxidation mechanism. This knowledge may also facilitate the successful coupling of valuable cathodic reactions, such as the hydrogen evolution reaction (HER) or CO₂ reduction, thereby substantially improving the overall utility of the PEC device.

All-Inorganic Halide Perovskite Nanocrystals (NCs) have emerged as a new class of fascinating nanomaterials with outstanding optoelectronic properties, with promise to revolutionize different disciplines like photovoltaics, lasing and emission. In the present talk, we will describe our efforts towards the application of these materials for solar-driven processes spanning from photocatalysis, environmental remediation,[1] H2 production and waste valorization.[2], We will discuss on the rational design of these fascinating materials towards photoelectrochemical processes, and the importance of extracting basic electronic and optical information to understand the carrier dynamics,[3] the influence of trap states and to define adequate defect passivation strategies to maximize the performance and stability of these materials. Moreover, proper interrogation tools are needed to validate their photoelectrocatalytic activity and selectivity. The development of autonomous photoelectrochemical devices based on these materials will be discussed on the basis of recent results from the European Innovation Coucil Project OHPERA. 

Transitioning away from fossil fuels in the energy and chemical sectors is crucial to achieving a sustainable and environmentally friendly future. One promising approach in this transition is the utilization of glycerol, a byproduct of biodiesel production, as a plentiful and renewable source for producing valuable chemicals. Glycerol's valorization not only provides a sustainable alternative to fossil fuels but also adds value to biodiesel production by converting its byproduct into high-value chemicals. However, the process of converting glycerol is complex due to the intricate reaction mechanisms involved, which significantly impact the selection of products. This study delves into the chemical selectivity of glycerol when catalyzed by various metallic surfaces, focusing on the use of specific descriptors for carbon (*C, *CH2OH) and oxygen (*O, CH3O). By employing linear regression analysis, we discovered that CH2OH and CH3O are superior descriptors compared to *C and *O, respectively. This superiority is attributed to their unique interactions with adjacent groups and specific bond characteristics, which influence the reaction intermediates and overall reaction pathway.

To validate these findings, we conducted multilinear regression analyses, further supporting the effectiveness of CH2OH and CH3O as descriptors. The research progressed by utilizing scaling relationships to develop selectivity maps for glycerol dehydrogenation. These maps serve as a valuable tool in identifying potential catalyst candidates by illustrating the selectivity trends based on the relative bond strengths of carbon and oxygen descriptors on different metallic surfaces. The study's results indicate that the first dehydrogenation step of glycerol can lead to two different intermediates, each bonded through either the secondary carbon or the secondary oxygen, depending on the relative bond strengths of the descriptors. In the subsequent dehydrogenation step, up to five intermediates may form, again influenced primarily by the bond strength interactions of carbon and oxygen with the catalyst surface. These detailed selectivity maps, in combination with kinetic considerations and experimental data, offer a comprehensive guide for selecting and optimizing catalysts for efficient glycerol dehydrogenation.

In conclusion, this research provides significant insights into the valorization of glycerol, highlighting the importance of selecting appropriate descriptors for understanding and controlling the reaction mechanisms involved. The development of selectivity maps presents a practical approach to predicting and enhancing catalyst performance, paving the way for more efficient and sustainable chemical production processes from glycerol. By addressing the complexities of glycerol valorization, this study contributes to the broader goal of transitioning away from fossil fuels. The findings emphasize the potential of using renewable feedstocks and advanced catalysis to produce high-value chemicals, supporting the shift towards a more sustainable and circular economy. This research not only advances the understanding of glycerol chemistry but also offers practical solutions for developing greener technologies in the energy and chemical sectors.

1. Introduction

Biodiesel, a clean and non-toxic biofuel, is gaining prominence in Europe, and its market is expected to grow [1]. However, during the process of converting plant oils or animal fats into biodiesel, about 10% of glycerol is produced as a by-product [2]. The excess glycerol production drives the need for new applications for its use [3]. This project aims to upgrade glycerol through electrochemical oxidation, reducing waste in the biofuel sector and yielding valuable products. Among all the glycerol derivatives, lactic acid, in particular, is in high demand within the food and pharmaceutical industries. It has been extensively used as a crucial monomer in the production of polylactic acid for manufacturing bio-based plastic [4]. In an electrolysis system resembling water electrolysis, the glycerol electrolysis couples hydrogen evolution reaction (HER) on the cathode side, while substituting the sluggish water oxidation (>1.23 VRHE) with glycerol electro-oxidation reaction (0.6-0.8 VRHE) on the anode side. This process offers a strategy for generating green hydrogen with lower energy requirement compared to water electrolysis. Simultaneously, it enables the co-production of lactic acid, which offers environmental advantages and economic benefits [5]. However, the challenge in this process is the selective production of lactic acid due to the competing reaction pathways for glycerol oxidation, resulting in producing various oxidation products and an increased separation costs downstream.

2. Materials and Methods

Commercial Pt nanoparticles supported on carbon (60 wt%, Pt/C) were employed to benchmark the reaction in an alkaline environment. Various metal oxide supports, such as aluminium oxides, are introduced to enhance the conversion of dihydroxyacetone to lactic acid. The properties of the aluminas are detailed in the table, including the commercial acidic alumina (Al2O3_A), Al2O3 nano powders (Al2O3_NPs), and basic alumina (Al2O3_B). The catalysts were prepared by spray-coating an ink containing Pt/C, which is mixed with metal oxides, to the surface of a carbon paper (Freudenberg H23), which served as a conductive substrate.

Glycerol electrolysis was conducted via chronopotentiometry and chronoamperometry in the Membrane Electrode Assembly cell at 60°C, coupled with online gas chromatography for hydrogen production detection. Following the electrolysis measurements, the electrolytes were collected and analysed using high-performance liquid chromatography to detect liquid oxidation products.

3. Results and Discussion

The results from chronopotentiometry show a stable performance under constant currents at 100 mA over one hour, with a gradual increase in the cell voltage from 0.6 to 0.9V. The resulting electrolytes were collected and analysed using the HPLC for the liquid products. The measurements were carried out on catalysts materials prepared by mixing Pt/C with different alumina materials. The lactic acid yield on Pt/C reaches around 40% and the lactic acid yield on PtC_Al2O3_NPs and PtC_Al2O3_A can reach 68%. The relevant characterisations of the materials and in-situ techniques will be discussed in the presentation.

4. Conclusion

This study demonstrates the effectiveness of the Pt-based materials for glycerol electro-oxidation at a low potential window in alkaline condition. The glycerol electrolysis enables production of H₂ at lower thermodynamic energy input than water electrolysis, meanwhile, allows the co-production of valuable products such as lactic acid, glycolic acid, glyceric acid, etc. The addition of aluminas with surface acidity promote the production of lactic acid from a yield of 40% on Pt/C to 68% on Pt/Al2O3 with acidic properties.

Electrocatalytic reactions play a central role in replacing a fossil fuel-based economy with systems based on renewable energy that provide green electricity and produce basic chemicals and fuels. Electrochemical splitting of water, for example, produces hydrogen at the cathode, which can be used as an energy carrier, fuel, or as a chemical in refining processes. Nevertheless, the slow kinetics of the oxygen evolution reaction (OER) at the anode and the need for scarce and expensive platinum group metals as highly active electrocatalyst materials hinder efficient water electrolysis on an industrially relevant scale. Therefore, the substitution of OER by the electrochemical alcohol oxidation reaction (AOR) using non-noble metal electrocatalysts could decrease the electrical energy and cost needed to produce hydrogen at the cathode, while also producing value-added chemicals at the anode.^[1-4] In particular, the electrooxidation of glycerol, a waste product of the biodiesel industry, is highly interesting since multiple products, all required in different industries, can be obtained.^[5] Still, controlling the reaction selectivity becomes a challenge. Suppressing the cleavage of the C-C bond over non-noble metal-based electrocatalysts is challenging. Often, only formate is reported as a major product, while C2 (e.g., oxalic acid) or C3 (e.g., glyceric acid) products are obtained in lower amounts.

In this communication, the electrocatalytic performance of several multi-metal-based catalysts based on Co, Cu, or Ni in the alcohol electrooxidation will be discussed. The first part of the talk will focus on understanding how tuning the Co:Cu ratio in a CoCu hydroxycarbonate impacts the activity and selectivity of different alcohols. In the presence of glycerol, in-situ leaching of Cu is observed, which leads to activation of the electrocatalyst. While the activity can be tuned, the selectivity remains unchanged, with formate being the only product.^[6]  Therefore, to suppress the C-C cleavage and increase the formation of C3 products, solketal, a mono alcohol obtained by acetal modification of glycerol, is electro-oxidized instead of glycerol.^[7] Using solketal, the stability of the Cu-based catalyst during the electrooxidation reaction is also modified. In the second part, ATR-IR spectroscopy and single-particle-on-the-nanoelectrode with identical-location transmission electron microscope provide additional insights into how the presence of solketal impacts the catalyst reconstruction and product formation, explaining the impact of Cu leaching on the GOR and SOR activity, in a CoNiFeCu multimetal electrocatalysts.

The efficient production of green hydrogen (gH2) is crucial for a sustainable energy transition. To reduce the costs associated with gH2 production via electrolysis, several challenges need to be addressed. For example, developing more efficient and stable anodes using accessible and widely available materials can help reduce capital and operational costs. The high overpotential required for water oxidation (OER, oxygen evolution reaction), including the most active materials for the reaction (Ir or Ru-based), is one of the main factors limiting the efficiency of these devices. In this context, replacing the OER at the anode in electrolyzers with the oxidation of biomass-derived substances can enhance overall efficiency by reducing the energy requirements of the devices and potentially producing valuable chemicals [1-2].

To produce a target chemical in an efficient and sustainable way, it is important to maximize the reaction activity and selectivity. This can be achieved by optimizing various components of the electrochemical device, including the electrode and electrolyte. Several biomass-derived molecules can be converted into valuable products, including various poly- and monosaccharides and polyols. In this context, glycerol, which is a model molecule for the oxidation of polyols and an abundant byproduct of biodiesel production [2], emerges as an interesting molecule for both fundamental and applied studies in this field.

Numerous studies have been published over the last few decades on the electro-oxidation of small organic molecules, using electrodes ranging from model surfaces like single crystals, which focus exclusively on fundamental aspects, to carbon and stainless steel, which focus on the viability of large-scale applications. It is well known that alcohols and polyols are oxidized on Pt- and Pd-based materials in alkaline media at much lower potentials than on materials based on non-noble metals [1]. Consequently, many studies have been conducted on these systems over the last few decades. However, many fundamental questions remain open in the field, such as how the structure of the catalysts influences the activity and selectivity and what role the electrolyte plays in the electrochemical reaction.

Therefore, in this talk, I will present results from my research group on the electro-oxidation of glycerol. I will focus on results obtained with polycrystalline Pt and analyze some fundamental aspects of the modification of the electrode by p-block adatoms and the effect of alkaline metal ions.

Glycerol, often regarded as a waste byproduct of biodiesel production, can be upgraded into various higher-value chemicals through selective partial oxidation. A promising ‘green’ pathway is the photoelectrochemical (PEC) oxidation of glycerol; due to the high value of the targeted products, such as dihydroxyacetone, this route offers a more favorable techno-economic case than, for example, PEC water splitting[RK1] . In this study, we present two key aspects of PEC glycerol oxidation using BiVO₄ thin films as a model photoanode. First, we explore the impact of the electrolyte on the PEC performance of BiVO₄. Our experimental findings demonstrate that both the anion and cation of the electrolyte profoundly influence performance, affecting parameters such as photocurrent, stability, and selectivity towards glycerol oxidation products. Notably, NaNO₃ is identified as the optimal electrolyte for PEC glycerol oxidation with BiVO₄, outperforming the previously favored Na₂SO₄. Second, we address the challenge of peak overlap in high-performance liquid chromatography (HPLC) analysis, particularly between glycerol, dihydroxyacetone, and formic acid. We propose a quantification protocol that resolves these peak overlaps using various detectors, including the refractive index (RI) and variable-wavelength UV detectors. Glycolaldehyde emerges as the most dominant product from BiVO₄.

The replacement of the traditionally applied anode half reaction, i.e., water oxidation (OER) with alternative oxidation reactions could significantly decrease the cell voltages in CO₂ electrolyzer cells in parallel with generating valuable platform chemicals. Besides the criteria typically well-addressed in (the not that numerous) studies (the reaction can be driven at considerably lower potentials compared to the OER in parallel with generating products that are more valuable than the substrate molecule) one aspect is almost always overlooked: the carbon-neutral/negative operation (from the cradle to the gate) of the complete process is ensured. Even though this is one of the most important requirements for the industrial deployment of CO₂ electrolysis technology. Quite a few reactions have been already considered from which the selective electrocatalytic oxidation of glycerol (GOR) seems to be a particularly promising direction. Unpurified (i.e., crude) glycerol (glycerol content is in between 45 to 80 wt%) can be accessed in large quantities from a relatively pure source (biodiesel/soap industry). Most of the studies in the literature use pure glycerol as the substrate even though purification of the reactant/product stream can significantly increase the carbon footprint potentially tipping out the carbon balance of the whole system.

In this study, CO2RR to CO was driven at the cathode (Ag nanoparticles), and the GOR was performed at the anode of a small (1 cm² active surface area) microfluidic electrolyzer cell utilizing crude glycerol (at least 80 wt% glycerol content) as the reactant. Due to the several impurities in crude glycerol (methanol, various (metal) ions, fatty acid residues and other organics) that can negatively affect the activity, selectivity and most importantly, the stability of the electrocatalysts, both noble metal (Pt and its bimetallic alloys), and non-noble metal based (Fe, and Ni-based single atom catalysts) electrocatalysts were screened. When pristine glycerol was replaced by crude glycerol, achievable current densities rapidly dropped for the noble metal samples along with a change in selectivity: still, a mixture of C1-C3 products formed (glycerate, glycolate, tartronate, oxalate, lactate and formate), but only 50% of the passed charge was consumed by their formation when Pt was used as the anode catalyst. Contrastingly, the major GOR product was formate (around 90% FE) in the case of all single atom catalysts regardless of the purity of the used glycerol source. Under optimal conditions, the paired CO2RR/GOR electrolyzer cell was operated for five hours at industrially relevant current densities (≈ 100 mA cm^-2) with stable CO2RR and GOR selectivity using a mixed Fe-Ni single atom catalyst as the anode and crude glycerol as the reactant.

Electro-oxidation of biomass derived species, such as glycerol and glucose, presents a sustainable approach for converting side streams into value-added products. Additionally, employing electro-oxidation of biomass offers an attractive alternative to the challenging oxygen evolution reaction in an anodic compartment. Electro-oxidation activity and selectivity depend on an electrocatalyst, but also on the electrode potential, the pH, and the electrolyte. For example, for broadly employed gold (Au) electrocatalysts, electro-oxidation activity of glycerol and glucose have been observed under alkaline conditions, whereas under acidic and neutral conditions, Au is almost inactive.

The characteristic of solid-liquid interface a play pivotal role in electrocatalysis. These interface properties can vary substantially depending e.g. on solvent and electrode potential and the variations can, in turn, have direct impact on electrocatalytic behaviour. The grand-canonical ensemble (GCE) DFT calculations  [1]  offer a robust framework for modelling electrochemical interfaces and reactions at the atomic level, while maintaining fixed electrode potentials but they are computationally more costly than standard canonical DFT calculations and not always possible for complex organic molecules.

Under electrocatalytic conditions, solvent-originating species may be present on the surface of the electrocatalyst, potentially influencing the electro-oxidation of biomass-derived organic compounds. To assess the presence or absence of species such as hydroxyls and oxygens, Pourbaix diagrams can be computed [2,3]  across varying electrocatalytic conditions. Our findings reveal that under oxidating potentials, the Au(111) surface contains OH groups at basic conditions, while no OH species are present at acidic conditions [2]  In contrast, on the Pt(111) surface [3], the Pourbaix diagrams are substantially more complex, highlighting the rich pattern of mixed O and OH overlayer structures at alkaline conditions.

In my presentation, I will also discuss how we employed DFT methods to analyse reaction mechanisms and energetics glycerol [2]  and glucose [4] electro-oxidation on Au(111) at varying electrocatalytic reaction conditions. The presence or absence of adsorbed OH groups significantly impact on electro-oxidation of organic species on Au(111), with alkaline conditions being energetically more favourable  giving an explantions for  the experimentally observed pH-dependent activity and selectivity under alkaline conditions.

Overall our results emphasize the importance of considering the electrocatalytic reaction conditions in calculations, as these conditions can have a substantial impact the reaction mechanism, thermodynamics, and kinetics, thus affecting the overall performance of the electrocatalyst.

Thanks to its wide availability, CO₂-neutrality and intrinsically renewable nature, biomass is emerging as a promising substitute to fossil fuels, and biomass electro-oxidation as an encouraging production route for hydrogen and value-added chemicals. To catalyse these electrochemical oxidation reactions, platinum group metals have emerged as promising candidates, showing good activity at low overpotentials. However, noble metals suffer from rapid and drastic activity drops, caused by the poisoning nature of some adsorptive species. The first step, to tackle this issue and to allow high reaction rates to be sustained for longer times, is the identification of these poisonous intermediates. This insight could guide either the development of mildly binding, poison-resistant catalyst, or the identification of potential pulsing protocols to recover the active sites.

For the specific case of platinum, while it is generally accepted that the formation of platinum oxides is responsible for the rapid Pt deactivation above 0.8V vs RHE, a similar activity decline is observed at lower potentials, the cause of which is less clear. In the case of glycerol oxidation, while the activity at 0.8V can be recovered by pulsing to mildly reductive potential (≈0.4V), this kind of pulsing has no effect on the catalytic activity at 0.6V, which can however be recovered by oxidative pulsing (1.2V). In a recent attempt to identify the poisonous intermediates, Chen et al. have proposed that glyceric acid could be blocking the surface at 0.6V, and reported increased glyceric acid selectivity by reductive pulsing.¹  Expanding on their work, here we combined surface enhanced infrared spectroscopy and potential pulsing to identify poisoning intermediates and improve the catalyst stability.

Our results show that not only carboxylate species, but also linear (1930-1970 cm^-1) and bridge-bonded (1700-1790 cm^-1) CO accumulate during both glycerol and formate oxidation. These CO intermediates show a blue shift compared to pure CO, of around 100 cm^-1, and twice as high Stark tuning slopes (of 120-50 cm^-1). This suggests the presence of partially hydrogenated CO adsorbates, previously observed in methanol oxidation.² What’s more, this hydrogenated form of CO appears to poison the active sites up to potentials as high as 0.9V vs RHE, largely above the oxidation potential of pure CO.

Our study shows how hydrogenated CO is an overlooked cause of Pt deactivation, and common to several oxidation reactions. The identification of the poisoning intermediates also provides insights into alleviating the blockage of sites, as for the case of CO, potential pulsing above 1.2V vs RHE was found to be an effective approach to reactive the catalyst.

Depleting reserves of fossil fuels and growing concerns with atmospheric CO₂ levels necessitate the development of non-petroleum derived, renewable fuels and carbon-based building blocks for chemical industries. Solar and Biomass refineries have been proposed as potential replacements for the current petroleum paradigm, and one possible way to convert wate biomass to added value chemicals while also reducing water or CO2 to fuels is a direct photoelectrochemical approach. Identifying semiconductor material and co-catalyst combinations that can selectively drive key photo-oxidation reactions at high photocurrent densities remains a challenge in the field. In this presentation progress in developing semiconductors as photoanodes is discussed. Results with oxides like WO3, BiVO4, and SrTiO3 will be presented as well as with using 2D-TMD materials (MoS2) and organic semiconductor bulk heterojunctions. The oxidation activity toward key model reactions of the oxidation of biomass-derived 2,5-hydroxylmethylfurfural (HMF) into 2,5-Furandicarboxaldehyde (DFF) and 2,5-furandicarboxylicacid (FDCA), and the oxidation of glycerol will be examined and factors that determine selectivity will be presented. Aspects of solar light harvesting, material nanostructure, electrocatalysis kinetics, and charge-carrier separation/transport are discussed.