• Energy Research

AbstractSolar fuels offer a promising approach to provide sustainable fuels by harnessing sunlight1,2. Following a decade of advancement, Cu2O photocathodes are capable of delivering a performance comparable to that of photoelectrodes with established photovoltaic materials3–5. However, considerable bulk charge carrier recombination that is poorly understood still limits further advances in performance6. Here we demonstrate performance of Cu2O photocathodes beyond the state-of-the-art by exploiting a new conceptual understanding of carrier recombination and transport in single-crystal Cu2O thin films. Using ambient liquid-phase epitaxy, we present a new method to grow single-crystal Cu2O samples with three crystal orientations. Broadband femtosecond transient reflection spectroscopy measurements were used to quantify anisotropic optoelectronic properties, through which the carrier mobility along the [111] direction was found to be an order of magnitude higher than those along other orientations. Driven by these findings, we developed a polycrystalline Cu2O photocathode with an extraordinarily pure (111) orientation and (111) terminating facets using a simple and low-cost method, which delivers 7 mA cm−2 current density (more than 70% improvement compared to that of state-of-the-art electrodeposited devices) at 0.5 V versus a reversible hydrogen electrode under air mass 1.5 G illumination, and stable operation over at least 120 h.

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.

Porous dendritic copper–indium metal alloy foam catalysts are interfaced with a perovskite‖BiVO4 tandem device for solar CO2-to-CO conversion under bias-free conditions using water as an electron donor.

AbstractThe production of clean fuels and chemicals from waste feedstocks is an appealing approach towards creating a circular economy. However, waste photoreforming commonly employs particulate photocatalysts, which display low product yields, selectivity, and reusability. Here, a perovskite‐based photoelectrochemical (PEC) device is reported, which produces H2 fuel and simultaneously reforms waste substrates. A novel Cu30Pd70 oxidation catalyst is integrated in the PEC device to generate value‐added products using simulated solar light, achieving 60–90% product selectivity and ≈70–130 µmol cm−2 h−1 product formation rates, which corresponds to 102–104 times higher activity than conventional photoreforming systems. The single‐light absorber device offers versatility in terms of substrate scope, sustaining unassisted photocurrents of 4–9 mA cm−2 for plastic, biomass, and glycerol conversion, in either a two‐compartment or integrated “artificial leaf” configuration. These configurations enable an effective reforming of non‐transparent waste streams and facile device retrieval from the reaction mixture. Accordingly, the presented PEC platform provides a proof‐of‐concept alternative towards photoreforming, approaching more closely the performance and versatility required for commercially viable waste utilization.

AbstractIdeonella sakaiensis (I. sakaiensis) can grow on polyethylene terephthalate (PET) as the major carbon and energy source. Previous work has shown that PET conversion in the presence of oxygen released carbon dioxide and water while yielding adenosine triphosphate (ATP) through oxidative phosphorylation. This study demonstrates that I. sakaiensis is a facultative anaerobe that ferments PET to the feedstock chemicals acetate and ethanol in the absence of oxygen. In addition to PET, the pure monomer ethylene glycol (EG), the intermediate product ethanol, and the carbohydrate fermentation test substance maltose can also serve as fermenting substrates. Co‐culturing of I. sakaiensis with the electrogenic and acetate‐consuming Geobacter sulfurreducens produced electricity from PET or EG. This newly identified plastic fermentation process by I. sakaiensis provides thus a novel biosynthetic route to produce high‐value chemicals or electricity from plastic waste streams.

The integration of the water-oxidation enzyme photosystem II (PSII) into electrodes allows the electrons extracted from water oxidation to be harnessed for enzyme characterization and to drive novel endergonic reactions. However, PSII continues to underperform in integrated photoelectrochemical systems despite extensive optimization efforts. Here we carried out protein-film photoelectrochemistry using spinach and Thermosynechococcus elongatus PSII, and we identified a competing charge transfer pathway at the enzyme-electrode interface that short-circuits the known water-oxidation pathway. This undesirable pathway occurs as a result of photo-induced O2 reduction occurring at the chlorophyll pigments and is promoted by the embedment of PSII in an electron-conducting fullerene matrix, a common strategy for enzyme immobilization. Anaerobicity helps to recover the PSII photoresponse and unmasks the onset potentials relating to the QA/QB charge transfer process. These findings impart a fuller understanding of the charge transfer pathways within PSII and at photosystem-electrode interfaces, which will lead to more rational design of pigment-containing photoelectrodes in general.

This tutorial review describes the physical–chemical aspects one must consider when building photocatalytic liposomes for solar fuel production.