Oxygen Functionalized Copper Nanoparticles for Solar-Driven Conversion of Carbon Dioxide to Methane

Direct Photocatalytic Methane Oxidation to Formaldehyde by N Doping Co-Decorated Mixed Crystal TiO2

In this paper, N-doped TiO2 mixed crystals are prepared via direct calcination of TiN for highly selective oxidation of CH4 to HCHO at room temperature. The structures of the prepared TiO2 samples are characterized to be N-doped TiO2 of anatase and rutile mixed crystals. The crystal structures of TiO2 samples are determined by XRD spectra and Raman spectra, while N doping is demonstrated by TEM mapping, ONH inorganic element analysis, and high-resolution XPS results. Significantly, the production rate of HCHO is as high as 23.5 mmol·g-1·h-1 with a selectivity over 90%. Mechanism studies reveal that H2O is the main oxygen source and acts through the formation of ·OH. DFT calculations indicate that the construction of a mixed crystal structure and N-doping modification mainly act by increasing the adsorption capacity of H2O. An efficient photocatalyst was prepared by us to convert CH4 to HCHO with high yield and selectivity, greatly promoting the development of the photocatalytic CH4 conversion study.

A Ni-O-Ag photothermal catalyst enables 103-m2 artificial photosynthesis with >17% solar-to-chemical energy conversion efficiency

The scalable artificial photosynthesis composed of photovoltaic electrolysis and photothermal catalysis is limited by inefficient photothermal CO2 hydrogenation under weak sunlight irradiation. Herein, NiO nanosheets supported with Ag single atoms [two-dimensional (2D) Ni1Ag0.02O1] are synthesized for photothermal CO2 hydrogenation to achieve 1065 mmol g-1 hour-1 of CO production rate under 1-sun irradiation. This performance is attributed to the coupling effect of Ag-O-Ni sites to enhance the hydrogenation of CO2 and weaken the CO adsorption, resulting in 1434 mmol g-1 hour-1 of CO yield at 300°C. Furthermore, we integrate the 2D Ni1Ag0.02O1-supported photothermal reverse water-gas shift reaction with commercial photovoltaic electrolytic water splitting to construct a 103-m2 scale artificial photosynthesis system (CO2 + H2O → CO + H2 + O2), which achieves more than 22 m3/day of green syngas with an adjustable H2/CO ratio (0.4-3) and a photochemical energy conversion efficiency of >17%. This research charts a promising course for designing practical, natural sunlight-driven artificial photosynthesis systems.

Rare-Earth-Modified Metal-Organic Frameworks and Derivatives for Photo/Electrocatalysis

Metal-organic frameworks (MOFs) and their derivatives have attracted much attention in the field of photo/electrocatalysis owing to their ultrahigh porosity, tunable properties, and superior coordination ability. Regulating the valence electronic structure and coordination environment of MOFs is an effective way to enhance their intrinsic catalytic performance. Rare earth (RE) elements with 4f orbital occupancy provide an opportunity to evoke electron rearrangement, accelerate charged carrier transport, and synergize the surface adsorption of catalysts. Therefore, the integration of RE with MOFs makes it possible to optimize their electronic structure and coordination environment, resulting in enhanced catalytic performance. In this review, progress in current research on the use of RE-modified MOFs and their derivatives for photo/electrocatalysis is summarized and discussed. First, the theoretical advantages of RE in MOF modification are introduced, with a focus on the roles of 4f orbital occupancy and RE ion organic coordination ligands. Then, the application of RE-modified MOFs and their derivatives in photo/electrocatalysis is systematically discussed. Finally, research challenges, future opportunities, and prospects for RE-MOFs are also discussed.

Scalable Edge-Oriented Metallic Two-Dimensional Layered Cu2Te Arrays for Electrocatalytic CO2 Methanation

Copper-based nanomaterials are compelling for high-efficient, low-cost electrocatalytic CO₂ reduction reaction (CO₂RR) due to their exotic electronic and structural properties. However, controllable preparation of copper-based two-dimensional (2D) materials with abundant catalytically active sites, that guarantee high CO₂RR performance, remains challenging, especially on a large scale. Here, an in situ vertical growth of scalable metallic 2D Cu₂Te nanosheet arrays on commercial copper foils is demonstrated for efficient CO₂-to-CH₄ electrocatalysis. The edge-oriented growth of Cu₂Te nanosheets with tunable sizes and thicknesses is facilely attained by a two-step process of chemical etching and chemical vapor deposition. These active sites abounding on highly exposed edges of Cu₂Te nanosheets greatly promote the electroreduction of CO₂ into CH₄ at a potential as low as -0.4 V (versus the reversible hydrogen electrode), while suppressing hydrogen evolution reaction. When a flow cell is employed to accelerate the mass transfer, the faradaic efficiency reaches ∼63% at an applied current density of 300 mA cm^-2. These findings will provide great possibilities for developing scalable, energy-efficient Cu-based CO₂RR electrocatalysts.

The Crystal Plane is not the Key Factor for CO2 -to-Methane Electrosynthesis on Reconstructed Cu2 O Microparticles

Cu₂ O microparticles with controllable crystal planes and relatively high stability have been recognized as a good platform to understand the mechanism of the electrocatalytic CO₂ reduction reaction (CO₂ RR). Herein, we demonstrate that the in situ generated Cu₂ O/Cu interface plays a key role in determining the selectivity of methane formation, rather than the initial crystal plane of the reconstructed Cu₂ O microparticles. Experimental results indicate that the methane evolution is dominated on all three different crystal planes with similar Tafel slopes and long-term stabilities. Density functional theory (DFT) calculations further reveal that *CO is protonated via a similar bridge configuration at the Cu₂ O/Cu interface, regardless of the initial crystal planes of Cu₂ O. The Gibbs free energy changes (ΔG) of *CHO on different reconstructed Cu₂ O planes are close and more negative than that of *OCCOH, indicating the methane formation is more favorable than ethylene on all Cu₂ O crystal planes.

Gold-like activity copper-like selectivity of heteroatomic transition metal carbides for electrocatalytic carbon dioxide reduction reaction

An overarching challenge of the electrochemical carbon dioxide reduction reaction (eCO₂RR) is finding an earth-abundant, highly active catalyst that selectively produces hydrocarbons at relatively low overpotentials. Here, we report the eCO₂RR performance of two-dimensional transition metal carbide class of materials. Our results indicate a maximum methane (CH₄) current density of −421.63 mA/cm² and a CH₄ faradic efficiency of 82.7% ± 2% for di-tungsten carbide (W₂C) nanoflakes in a hybrid electrolyte of 3 M potassium hydroxide and 2 M choline-chloride. Powered by a triple junction photovoltaic cell, we demonstrate a flow electrolyzer that uses humidified CO₂ to produce CH₄ in a 700-h process under one sun illumination with a CO₂RR energy efficiency of about 62.3% and a solar-to-fuel efficiency of 20.7%. Density functional theory calculations reveal that dissociation of water, chemisorption of CO₂ and cleavage of the C-O bond—the most energy consuming elementary steps in other catalysts such as copper—become nearly spontaneous at the W₂C surface. This results in instantaneous formation of adsorbed CO—an important reaction intermediate—and an unlimited source of protons near the tungsten surface sites that are the main reasons for the observed superior activity, selectivity, and small potential.

It is of high interests to develop new catalysts for selective CO2 electroreduction. Here the authors investigate two-dimensional transition metal carbides for CO2 to methane conversion with superior activity, selectivity and low overpotentials.

Cu Nanocluster-Loaded TiO2 Nanosheets for Highly Efficient Generation of CO-Free Hydrogen by Selective Photocatalytic Dehydrogenation of Methanol to Formaldehyde

Safe storage and transportation of H₂ is a fundamental requirement for its wide applications in the future. Controllable release of high-purity H₂ from a stable storage medium such as CH₃OH before use offers an efficient way of achieving this purpose. In our case, Cu nanoclusters uniformly dispersed onto (001) surfaces of TiO₂ nanosheets (TiO₂/Cu) are selectively prepared by thermal treatment of HKUST-1 loaded TiO₂ nanosheets. One of the TiO₂/Cu composites, TiO₂/Cu_50, exhibits remarkably high activity toward the selective dehydrogenation of CH₃OH to HCHO with a H₂ evolution rate of 17.8 mmol h^-1 per gram of catalyst within a 16-h photocatalytic reaction (quantum efficiency at 365 nm: 16.4%). Theoretical calculations reveal that interactions of Cu nanoclusters with TiO₂ could affect their electronic structures, leading to higher adsorption energy of CH₃OH at Ti sites and a lower barrier for the dehydrogenation of CH₃OH by the synergistic effect of Cu nanoclusters and TiO₂, and lower Gibbs free energy for desorption HCHO and H₂ as well.

Electrocatalysis for CO2 conversion: from fundamentals to value-added products

This timely and comprehensive review mainly summarizes advances in heterogeneous electroreduction of CO₂: from fundamentals to value-added products.

Kinetically Stable Oxide Overlayers on Mo3 P Nanoparticles Enabling Lithium-Air Batteries with Low Overpotentials and Long Cycle Life

The main drawbacks of today's state-of-the-art lithium-air (Li-air) batteries are their low energy efficiency and limited cycle life due to the lack of earth-abundant cathode catalysts that can drive both oxygen reduction and evolution reactions (ORR and OER) at high rates at thermodynamic potentials. Here, inexpensive trimolybdenum phosphide (Mo₃ P) nanoparticles with an exceptional activity-ORR and OER current densities of 7.21 and 6.85 mA cm^-2 at 2.0 and 4.2 V versus Li/Li⁺ , respectively-in an oxygen-saturated non-aqueous electrolyte are reported. The Tafel plots indicate remarkably low charge transfer resistance-Tafel slopes of 35 and 38 mV dec^-1 for ORR and OER, respectively-resulting in the lowest ORR overpotential of 4.0 mV and OER overpotential of 5.1 mV reported to date. Using this catalyst, a Li-air battery cell with low discharge and charge overpotentials of 80 and 270 mV, respectively, and high energy efficiency of 90.2% in the first cycle is demonstrated. A long cycle life of 1200 is also achieved for this cell. Density functional theory calculations of ORR and OER on Mo₃ P (110) reveal that an oxide overlayer formed on the surface gives rise to the observed high ORR and OER electrocatalytic activity and small discharge/charge overpotentials.