Santiago Rodríguez-Jiménez

Paired electrolysis enables the simultaneous coupling of the CO2 reduction reaction (CO2RR) with anodic waste valorisation to form valuable products, but achieving selective, efficient and stable product formation remains a challenge. In this study, W-containing formate dehydrogenase (FDH) from Nitratidesulfovibrio vulgaris Hildenborough is immobilised onto an electrode made from carbon felt coated with porous TiO2 and paired with commercial Ni foam to demonstrate the first enzymatic flow electrolyser for the simultaneous conversion of CO2 and waste (plastic and biomass) to the single product formate. The enzymatic flow electrolyser achieved a combined faradaic efficiency (FE) towards formate of almost 200% for both electrodes and can operate at an unprecedently low full-cell voltage of −1.5 V for 122 h. The aqueous formate produced in the semiartificial electrolyser was further utilised downstream as a C1 building block in the photocatalytic hydrocarboxylation of alkenes, providing a path for the domino valorisation of CO2 and waste towards bulk and fine chemical synthesis.

The solar-driven valorization of CO₂ to fuels and chemicals provides an exciting opportunity to develop a circular chemical industry, but the controlled production of multicarbon organics remains a major challenge.

The integration of enzymes with semiconductor light absorbers in semiartificial photosynthetic assemblies offers an emerging strategy for solar fuel production. However, such colloidal biohybrid systems rely currently on sacrificial reagents, and semiconductor-enzyme powder systems that couple fuel production to water oxidation are therefore needed to mimic an overall photosynthetic reaction. Here, we present a Z-scheme colloidal enzyme system that produces fuel with electrons sourced from water. This "closed-cycle" semiartificial approach utilizes particulate SrTiO₃:La,Rh and BiVO₄:Mo (light absorbers), hydrogenase or formate dehydrogenase (cocatalyst), and a molecular cobalt complex (a redox mediator). Under simulated solar irradiation, this system continuously generates molecular hydrogen or formate, while co-producing molecular oxygen for 10 h using only sunlight, water, and carbon dioxide as inputs. In-depth analysis using quartz crystal microbalance, photoelectrochemical impedance spectroscopy, transient photocurrent spectroscopy, and intensity-modulated photovoltage spectroscopy provides mechanistic understanding and characterization of the semiconductor-enzyme hybrid interface. This study provides a rational platform to assemble functional semiartificial colloidal Z-scheme systems for solar fuel synthesis.

The sunlight-driven reduction of CO₂ into fuels and platform chemicals is a promising approach to enable a circular economy. However, established optimization approaches are poorly suited to multivariable multimetric photocatalytic systems because they aim to optimize one performance metric while sacrificing the others and thereby limit overall system performance. Herein, we address this multimetric challenge by defining a metric for holistic system performance that takes multiple figures of merit into account, and employ a machine learning algorithm to efficiently guide our experiments through the large parameter matrix to make holistic optimization accessible for human experimentalists. As a test platform, we employ a five-component system that self-assembles into photocatalytic micelles for CO₂-to-CO reduction, which we experimentally optimized to simultaneously improve yield, quantum yield, turnover number, and frequency while maintaining high selectivity. Leveraging the data set with machine learning algorithms allows quantification of each parameter's effect on overall system performance. The buffer concentration is unexpectedly revealed as the dominating parameter for optimal photocatalytic activity, and is nearly four times more important than the catalyst concentration. The expanded use and standardization of this methodology to define and optimize holistic performance will accelerate progress in different areas of catalysis by providing unprecedented insights into performance bottlenecks, enhancing comparability, and taking results beyond comparison of subjective figures of merit.

Solar hydrogen production has been established by interfacing cyanamide modified graphitic carbon nitride (^NCNCN_X) with [FeFe]-hydrogenase via electrostatic interaction. QCM, PEIS, IMVS, and TPC reveal the importance of specific interaction.

Electrocatalytic CO₂ reduction has developed into a broad field, spanning fundamental studies of enzymatic ‘model’ catalysts to synthetic molecular catalysts and heterogeneous gas diffusion electrodes producing commercially relevant quantities of product. This diversification has resulted in apparent differences and a disconnect between seemingly related approaches when using different types of catalysts. Enzymes possess discrete and well understood active sites that can perform reactions with high selectivity and activities at their thermodynamic limit. Synthetic small molecule catalysts can be designed with desired active site composition but do not yet display enzyme‐like performance. These properties of the biological and small molecule catalysts contrast with heterogeneous materials, which can contain multiple, often poorly understood active sites with distinct reactivity and therefore introducing significant complexity in understanding their activities. As these systems are being better understood and the continuously improving performance of their heterogeneous active sites closes the gap with enzymatic activity, this performance difference between heterogeneous and enzymatic systems begins to close. This convergence removes the barriers between using different types of catalysts and future challenges can be addressed without multiple efforts as a unified picture for the biological‐synthetic catalyst spectrum emerges.

Electrocatalytic CO₂ reduction has developed into a broad field, spanning fundamental studies of enzymatic ‘model’ catalysts to synthetic molecular catalysts and heterogeneous gas diffusion electrodes producing commercially relevant quantities of product. This diversification has resulted in apparent differences and a disconnect between seemingly related approaches when using different types of catalysts. Enzymes possess discrete and well understood active sites that can perform reactions with high selectivity and activities at their thermodynamic limit. Synthetic small molecule catalysts can be designed with desired active site composition but do not yet display enzyme‐like performance. These properties of the biological and small molecule catalysts contrast with heterogeneous materials, which can contain multiple, often poorly understood active sites with distinct reactivity and therefore introducing significant complexity in understanding their activities. As these systems are being better understood and the continuously improving performance of their heterogeneous active sites closes the gap with enzymatic activity, this performance difference between heterogeneous and enzymatic systems begins to close. This convergence removes the barriers between using different types of catalysts and future challenges can be addressed without multiple efforts as a unified picture for the biological‐synthetic catalyst spectrum emerges.

This work demonstrates the simultaneous upcycling of all components in lignocellulosic biomass together with the greenhouse gas CO₂ as an attractive opportunity to synthesise sustainable and valuable chemicals.

Light-driven conversion of CO₂ to chemicals provides a sustainable alternative to fossil fuels, but homogeneous systems are typically limited by cross reactivity between different redox half reactions and inefficient charge separation. Herein, we present the bioinspired development of amphiphilic photosensitizer and catalyst pairs that self-assemble in lipid membranes to overcome some of these limitations and enable photocatalytic CO₂ reduction in liposomes using precious metal-free catalysts. Using sodium ascorbate as a sacrificial electron source, a membrane-anchored alkylated cobalt porphyrin demonstrates higher catalytic CO production (1456 vs 312 turnovers) and selectivity (77 vs 11%) compared to its water-soluble nonalkylated counterpart. Time-resolved and steady-state spectroscopy revealed that self-assembly facilitates this performance enhancement by enabling a charge-separation state lifetime increase of up to two orders of magnitude in the dye while allowing for a ninefold faster electron transfer to the catalyst. Spectroelectrochemistry and density functional theory calculations of the alkylated Co porphyrin catalyst support a four-electron-charging mechanism that activates the catalyst prior to catalysis, together with key catalytic intermediates. Our molecular liposome system therefore benefits from membrane immobilization and provides a versatile and efficient platform for photocatalysis.