The 2022 solar fuels roadmap Segev, Gideon; Kibsgaard, Jakob; Hahn, Christopher ...
Journal of physics. D, Applied physics,
08/2022, Letnik:
55, Številka:
32
Journal Article
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Abstract
Renewable fuel generation is essential for a low carbon footprint economy. Thus, over the last five decades, a significant effort has been dedicated towards increasing the performance of ...solar fuels generating devices. Specifically, the solar to hydrogen efficiency of photoelectrochemical cells has progressed steadily towards its fundamental limit, and the faradaic efficiency towards valuable products in CO
2
reduction systems has increased dramatically. However, there are still numerous scientific and engineering challenges that must be overcame in order to turn solar fuels into a viable technology. At the electrode and device level, the conversion efficiency, stability and products selectivity must be increased significantly. Meanwhile, these performance metrics must be maintained when scaling up devices and systems while maintaining an acceptable cost and carbon footprint. This roadmap surveys different aspects of this endeavor: system benchmarking, device scaling, various approaches for photoelectrodes design, materials discovery, and catalysis. Each of the sections in the roadmap focuses on a single topic, discussing the state of the art, the key challenges and advancements required to meet them. The roadmap can be used as a guide for researchers and funding agencies highlighting the most pressing needs of the field.
Arrays of graphene solution‐gated field‐effect transistors are fabricated for the detection of electrical activity of electrogenic cells. Cardiomyocyte‐like cells are cultured on the transistor ...arrays and their action potentials are detected by the underlying transistors. The analysis of the recorded cell signals and the electronic noise of the transistors confirm that graphene transistors surpass state‐of‐the‐art devices for bioelectronic applications.
Colloidal self-assembly allows rational design of structures on the micrometer and submicrometer scale. One architecture that can generate complete three-dimensional photonic bandgaps is the diamond ...cubic lattice, which has remained difficult to realize at length scales comparable with the wavelength of visible or ultraviolet light. In this work, we demonstrate three-dimensional photonic crystals self-assembled from DNA origami that act as precisely programmable patchy colloids. Our DNA-based nanoscale tetrapods crystallize into a rod-connected diamond cubic lattice with a periodicity of 170 nanometers. This structure serves as a scaffold for atomic-layer deposition of high-refractive index materials such as titanium dioxide, yielding a tunable photonic bandgap in the near-ultraviolet.
The hydrogen energy provided by solar-driven photoelectrochemical (PEC) water splitting must be greater than the energy used to produce and operate the technology, as a fundamental system requirement ...to enable energetic benefits to society. PEC H sub(2) production will require significant advances from both basic scientific research and applied technology development, prior to manufacturing and field deployment. To identify opportunities and priorities, here we use prospective life cycle system modeling to investigate the net-energy significance of six characteristics describing the PEC life cycle: (1) embodied energy of active cell materials, (2) embodied energy of inactive module materials, (3) energy intensity of active cell fabrication, (4) energy intensity of PEC module assembly, (5) initial energy use for production of balance-of-system (BOS), and (6) ongoing energy use for operation and end-of-life of BOS. We develop and apply a system model describing material and energy flows during the full life cycle of louvered thin-film PEC cells and their associated modules and BOS components. We find that fabrication processes for the PEC cells, especially the thin-film deposition of active cell materials, are important drivers of net energy performance. Nevertheless, high solar-to-hydrogen (STH) conversion efficiency and long cell life span are primary design requirements for PEC systems, even if such performance requires additional energy and material inputs for production and operation. We discuss these and other system dynamics, and highlight pathways to improve net energy performance.
Tailoring optical properties in photocatalysts by nanostructuring them can help increase solar light harvesting efficiencies in a wide range of materials. Whereas plasmon resonances are widely ...employed in metallic catalysts for this purpose, latest advances of nonradiative, dielectric nanophotonics also enable light confinement and enhanced visible light absorption in semiconductors. Here, a design procedure for large‐scale nanofabrication of semiconductor photoelectrodes using imprint lithography is developed. Anapole excitations and metasurface lattice resonances are combined to enhance the absorption of the model material, amorphous gallium phosphide (a‐GaP), over the visible spectrum. It is shown that cost‐effective, high sample throughput is achieved while retaining the precise signature of the engineered photonic states. Photoelectrochemical measurements under hydrogen evolution reaction conditions and sunlight illumination reveal the contributions of the respective resonances and demonstrate an overall photocurrent enhancement of 5.7, compared to a planar film. These results are supported by optical and numerical analysis of single nanodisks and of the upscaled metasurface.
Amorphous gallium phosphide acting as model semiconductor photocatalyst is top‐down nanostructured into a 25 mm2 photoelectrode with nanoimprint lithography. The engineered photonic states—anapole excitation and lattice resonance—promote broadband light trapping into the sub‐micrometer resonators. A comparison between the metasurface photoelectrode and a planar film under hydrogen evolution reaction conditions and sunlight illumination shows a nearly sixfold photocurrent enhancement.
A new method for achieving high efficiency planar CH3NH3I3–x Cl x perovskite photovoltaics, based on a low pressure, reduced temperature vapor annealing is demonstrated. Heterojunction devices based ...on this hybrid halide perovskite exhibit a top PCE of 16.8%, reduced J–V hysteresis, and highly repeatable performance without need for a mesoporous or nanocrystalline metal oxide layer. Our findings demonstrate that large hysteresis is not an inherent feature of planar heterojunctions, and that efficient charge extraction can be achieved with uniform halide perovskite materials with desired composition. X-ray diffraction, valence band spectroscopy, and transient absorption measurements of these thin films reveal that structural modifications induced by chlorine clearly dominate over chemical and electronic doping effects, without affecting the Fermi level or photocarrier lifetime in the material.
The coupling of CO-generating molecular catalysts with copper electrodes in tandem schemes is a promising strategy to boost the formation of multi-carbon products in the electrocatalytic reduction of ...CO2. While the spatial distribution of the two components is important, this aspect remains underexplored for molecular-based tandem systems. Herein, we address this knowledge gap by studying tandem catalysts comprising Co-phthalocyanine (CoPc) and Cu nanocubes (Cucub). In particular, we identify the importance of the relative spatial distribution of the two components on the performance of the tandem catalyst by preparing CoPc-Cucub/C, wherein the CoPc and Cucub share an interface, and CoPc-C/Cucub, wherein the CoPc is loaded first on carbon black (C) before mixing with the Cucub. The electrocatalytic measurements of these two catalysts show that the faradaic efficiency towards C2 products almost doubles for the CoPc-Cucub/C, whereas it decreases by half for the CoPc-C/Cucub, compared to the Cucub/C. Our results highlight the importance of a direct contact between the CO-generating molecular catalyst and the Cu to promote C–C coupling, which hints at a surface transport mechanism of the CO intermediate between the two components of the tandem catalyst instead of a transfer via CO diffusion in the electrolyte followed by re-adsorption.
Achieving stable operation of photoanodes used as components of solar water splitting devices is critical to realizing the promise of this renewable energy technology. It is shown that p-type ...transparent conducting oxides (p-TCOs) can function both as a selective hole contact and corrosion protection layer for photoanodes used in light-driven water oxidation. Using NiCo2O4 as the p-TCO and n-type Si as a prototypical light absorber, a rectifying heterojunction capable of light driven water oxidation was created. By placing the charge separating junction in the Si using a np+ structure and by incorporating a highly active heterogeneous Ni–Fe oxygen evolution catalyst, efficient light-driven water oxidation can be achieved. In this structure, oxygen evolution under AM1.5G illumination occurs at 0.95 V vs RHE, and the current density at the reversible potential for water oxidation (1.23 V vs RHE) is >25 mA cm–2. Stable operation was confirmed by observing a constant current density over 72 h and by sensitive measurements of corrosion products in the electrolyte. In situ Raman spectroscopy was employed to investigate structural transformation of NiCo2O4 during electrochemical oxidation. The interface between the light absorber and p-TCO is crucial to produce selective hole conduction to the surface under illumination. For example, annealing to produce more crystalline NiCo2O4 produces only small changes in its hole conductivity, while a thicker SiO x layer is formed at the n-Si/p-NiCo2O4 interface, greatly reducing the PEC performance. The generality of the p-TCO protection approach is demonstrated by multihour, stable, water oxidation with n-InP/p-NiCo2O4 heterojunction photoanodes.
The path to realizing low-cost, stable, and earth-abundant photoelectrodes can be enabled through a detailed understanding of the optoelectronic properties of these materials by combining theory and ...experimental techniques. Of the limited set of oxide photocathode materials currently available, CuFeO2 has emerged as a promising candidate warranting detailed attention. In this work, highly compact thin films of rhombohedral (3R) CuFeO2 were prepared via reactive co-sputtering. Despite its 1.43 eV indirect band gap, a cathodic photocurrent of 0.85 mA/cm2 was obtained at 0.4 V versus reversible hydrogen electrode in the presence of a sacrificial electron acceptor. This unexpected performance was related to inefficient bulk charge separation because of the ultrafast (<1 ps) self-trapping of photogenerated free carriers. The electronic structure of 3R-CuFeO2 was elucidated through a combination of optical and X-ray spectroscopic techniques and further complemented by first-principles computational methods including a many-body approach for computing the O K-edge X-ray absorption spectrum. Through resonant inelastic X-ray scattering spectroscopy, the visible absorption edges of CuFeO2 were found to correspond to Cu → Fe metal-to-metal charge transfer, which exhibits a high propensity toward self-trapping. Findings of the present work enable us to understand the performance bottlenecks of CuFeO2 photocathodes and suggest feasible strategies for improving material limitations.
Inverted planar heterojunction perovskite solar cells based on all-inorganic selective contact layers show great promise for commercialization owing to their competitiveness in terms of cost and ...stability. However, the power conversion efficiencies (PCEs) of the few reported perovskite solar cells with this type of device structure have been limited by relatively low photovoltages. Here, we propose a new device structure comprising electron beam-evaporated nickel and niobium oxides as the hole and electron selective contact layers, respectively. We demonstrate that a metal oxide material can be directly deposited on a perovskite film by electron beam evaporation without damaging the interface. We propose that the turn-on voltage of the p–n junction formed by the selective contacts represents a quantitative proxy of the charge blocking performance. A high turn-on voltage of 1.36 V is obtained for the NiO x /Nb2O5 p–n junction. An open-circuit voltage of 1.16 V is achieved using a hybrid organic–inorganic perovskite with a band gap of 1.6 eV. The large photovoltage, enabled by the excellent charge extraction and blocking properties of the inorganic selective contact layers, leads to the highest PCE of over 19.0% for this class of device.
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