Plasmonic Ag-decorated Cu2O nanowires for boosting photoelectrochemical CO2 reduction to multi-carbon products

Efficient Cu2O Photocathodes for Aqueous Photoelectrochemical CO2 Reduction to Formate and Syngas

Photoelectrochemical carbon dioxide reduction (PEC-CO2R) represents a promising approach for producing renewable fuels and chemicals using solar energy. However, attaining even modest solar-to-fuel (STF) conversion efficiency often necessitates the use of costly semiconductors and noble-metal catalysts. Herein, we present a Cu2O/Ga2O3/TiO2 photocathode modified with Sn/SnOx catalysts through a simple photoelectrodeposition method. It achieves a remarkable half-cell STF efficiency of ∼0.31% for the CO2R in aqueous KHCO3 electrolyte, under AM 1.5 G illumination. The system enables efficient production of syngas (FE: ∼62%, CO/H2 ≈ 1:2) and formate (FE: ∼38%) with a consistent selectivity over a wide potential range, from +0.34 to -0.16 V vs the reversible hydrogen electrode. We ascribe the observed performance to the favorable optoelectronic characteristics of our Cu2O heterostructure and the efficient Sn/SnOx catalysts incorporated in the PEC-CO2R reactions. Through comprehensive experimental investigations, we elucidate the indispensable role of Cu2O buried p-n junctions in generating a high photovoltage (∼1 V) and enabling efficient bulk charge separation (up to ∼70% efficiency). Meanwhile, we discover that the deposited Sn/SnOx catalysts have critical dual effects on the overall performance of the PEC devices, serving as active CO2R catalysts as well as the semiconductor front contact. It could facilitate interfacial electron transfer between the catalysts and the semiconductor device for CO2R by establishing a barrier-free ohmic contact.

Cascade signal amplification using Hg2+-induced oxidation of silver nanoparticles and cation exchange reaction for ICP-MS bioassay

Combining the Hg2+-induced oxidization of silver nanoparticles with the cation exchange reaction between Ag+ and CuS nanoparticles for cascade signal amplification, a sensitive, universal and label-free ICP-MS bioassay for nucleic acids and proteins was developed. By replacing the loop sequence of the T-Hg-T hairpin structure with specific sequences or aptamers to different biomarkers, it has great promise for the early detection of biomarkers potentially for diagnosis of cancerous diseases.

Seedless wet synthesis of copper-twinned nanocrystals

The wet synthesis of copper (Cu)-twinned nanostructures often requires the addition of noble metal seeds, as twinned Cu seeds are prone to oxidative etching, which inevitably introduces other metal species. In this study, a universal and seedless wet method is proposed for the synthesis of various Cu-twinned nanostructures, such as large Cu decahedrons (with sizes up to 300 nm), singly twinned Cu right bipyramids, and Cu nanorods. The amount of chloride ions (Cl-) and oleylamine and an optimal heating rate at the initial stage were proven to be crucial in this synthesis. Theoretical results revealed that the amount of Cl- could adjust the Gibbs free energy of Cu seeds by promoting the dissociation of oleylamine, which, in turn, determined the structure of thermodynamically favorable seeds based on the thermodynamic model. To the best of our knowledge, this is the first report on large Cu decahedrons and singly twinned Cu right bipyramids. Moreover, they both showed strong localized surface plasmon resonance in the near-infrared region. The photothermal conversion efficiency of large Cu decahedrons increased up to 52.9% upon 808 nm laser irradiation, which is the highest value ever reported for Cu nanocrystals.

Solar-CO2 -to-Syngas Conversion Enabled by Precise Charge Transport Modulation

The rational design of the directional charge transfer channel represents an important strategy to finely tune the charge migration and separation in photocatalytic CO2 -to-fuel conversion. Despite the progress made in crafting high-performance photocatalysts, developing elegant photosystems with precisely modulated interfacial charge transfer feature remains a grand challenge. Here, a facile one-pot method is developed to achieve in situ self-assembly of Pd nanocrystals (NYs) on the transition metal chalcogenide (TMC) substrate with the aid of a non-conjugated insulating polymer, i.e., branched polyethylenimine (bPEI), for photoreduction of CO2 to syngas (CO/H2 ). The generic reducing capability of the abundant amine groups grafted on the molecular backbone of bPEI fosters the homogeneous growth of Pd NYs on the TMC framework. Intriguingly, the self-assembled TMCs@bPEI@Pd heterostructure with bi-directional spatial charge transport pathways exhibit significantly boosted photoactivity toward CO2 -to-syngas conversion under visible light irradiation, wherein bPEI serves as an efficient hole transfer mediator, and simultaneously Pd NYs act as an electron-withdrawing modulator for accelerating spatially vectorial charge separation. Furthermore, in-depth understanding of the in situ formed intermediates during the CO2 photoreduction process are exquisitely probed. This work provides a quintessential paradigm for in situ construction of multi-component heterojunction photosystem for solar-to-fuel energy conversion.

Modulating the Cu2O Photoelectrode/Electrolyte Interface with Bilayer Surfactant Simulating Cell Membranes for Boosting Photoelectrochemical CO2 Reduction

The low solubility of CO₂ molecules and the competition of the hydrogen evolution reaction (HER) in aqueous electrolytes pose significant challenges to the current photoelectrochemical (PEC) CO₂ reduction reaction. In this study, inspired by the bilayer phospholipid molecular structure of cell membranes, we developed a Cu₂O/Sn photocathode that was modified with the bilayer surfactant DHAB for achieving high CO₂ permeability and suppressed HER. The Cu₂O/Sn/DHAB photocathode stabilizes the *OCHO intermediate and facilitates the production of HCOOH. Our findings show that the Faradaic efficiency (FE) of HCOOH by the Cu₂O/Sn/DHAB photoelectrode is 83.3%, significantly higher than that achieved with the Cu₂O photoelectrode (FE_HCOOH = 30.1%). Furthermore, the FE_H2 produced by the Cu₂O/Sn/DHAB photoelectrode is only 2.95% at -0.6 V vs RHE. The generation rate of HCOOH by the Cu₂O/Sn/DHAB photoelectrode reaches 1.52 mmol·cm^-2·h^-1·L^-1 at -0.7 V vs RHE. Our study provides a novel approach for the design of efficient photocathodes for CO₂ reduction.

Hydrophobic surface efficiently boosting Cu2O nanowires photoelectrochemical CO2 reduction activity

The limited mass transfer of CO₂ and the competitive hydrogen evolution reaction (HER) during photoelectrochemical (PEC) CO₂ reduction usually result in low CO₂ reduction activity. Here, we constructed a Cu₂O/Sn/PTFE photocathode with a hydrophobic surface based on Cu₂O by physical vapor deposition and a dipping method. The CO faradaic efficiency (FE) increased from 34.5% (Cu₂O) to 95.1% (Cu₂O/Sn/PTFE) at -0.7 V vs. RHE, and the FE_H2 decreased from 27.9% (Cu₂O) to 3.8% (Cu₂O/Sn/PTFE). The introduction of the hydrophobic layer enhances the local CO₂ concentration on the electrode surface and effectively isolates H⁺ from the aqueous electrolyte, thereby enhancing the CO₂ reduction activity.

Converting CO2 into Value-Added Products by Cu2 O-Based Catalysts: From Photocatalysis, Electrocatalysis to Photoelectrocatalysis

Converting CO₂ into value-added products by photocatalysis, electrocatalysis, and photoelectrocatalysis is a promising method to alleviate the global environmental problems and energy crisis. Among the semiconductor materials applied in CO₂ catalytic reduction, Cu₂ O has the advantages of abundant reserves, low price and environmental friendliness. Moreover, Cu₂ O has unique adsorption and activation properties for CO₂ , which is conducive to the generation of C₂₊ products through CC coupling. This review introduces the basic principles of CO₂ reduction and summarizes the pathways for the generation of C₁ , C₂ , and C₂₊ products. The factors affecting CO₂ reduction performance are further discussed from the perspective of the reaction environment, medium, and novel reactor design. Then, the properties of Cu₂ O-based catalysts in CO₂ reduction are summarized and several optimization strategies to enhance their stability and redox capacity are discussed. Subsequently, the application of Cu₂ O-based catalysts in photocatalytic, electrocatalytic, and photoelectrocatalytic CO₂ reduction is described. Finally, the opportunities, challenges and several research directions of Cu₂ O-based catalysts in the field of CO₂ catalytic reduction are presented, which is guidance for its wide application in the energy and environmental fields is provided.