Achieving Simultaneous CO2and H2S Conversion via a Coupled Solar-Driven Electrochemical Approach on Non-Precious-Metal Catalysts

Review of Theoretical and Computational Studies of Bulk and Single Atom Catalysts for H2 S Catalytic Conversion

Catalytic conversion of hydrogen sulfide (H2 S) plays a vital role in environmental protection and safety production. In this review, recent theoretical advances for catalytic conversion of H2 S are systemically summarized. Firstly, different mechanisms of catalytic conversion of H2 S are elucidated. Secondly, theoretical studies of catalytic conversion of H2 S on surfaces of metals, metal compounds, and single-atom catalysts (SACs) are systematically reviewed. In the meantime, various strategies which have been adopted to improve the catalytic performance of catalysts in the catalytic conversion of H2 S are also reviewed, mainly including facet morphology control, doped heteroatoms, metal deposition, and defective engineering. Finally, new directions of catalytic conversion of H2 S are proposed and potential strategies to further promote conversion of H2 S are also suggested: including SACs, double atom catalysts (DACs), single cluster catalysts (SCCs), frustrated Lewis pairs (FLPs), etc. The present comprehensive review can provide an insight for the future development of new catalysts for the catalytic conversion of H2 S.

Coupling Value-Added Anodic Reactions with Electrocatalytic CO2 Reduction

Electrocatalytic CO₂ reduction features a promising approach to realize carbon neutrality. However, its competitiveness is limited by the sluggish oxygen evolution reaction (OER) at anode, which consumes a large portion of energy. Coupling value-added anodic reactions with CO₂ electroreduction has been emerging as a promising strategy in recent years to enhance the full-cell energy efficiency and produce valuable chemicals at both cathode and anode of the electrolyzer. This review briefly summarizes recent progresses on the electrocatalytic CO₂ reduction, and the economic feasibility of different CO₂ electrolysis systems is discussed. Then a comprehensive summary of recent advances in the coupled electrolysis of CO₂ and potential value-added anodic reactions is provided, with special focus on the specific cell designs. Finally, current challenges and future opportunities for the coupled electrolysis systems are proposed, which are targeted to facilitate progress in this field and push the CO₂ electrolyzers to a more practical level.

Fight for carbon neutrality with state-of-the-art negative carbon emission technologies

After the Industrial Revolution, the ever-increasing atmospheric CO2 concentration has resulted in significant problems for human beings. Nearly all countries in the world are actively taking measures to fight for carbon neutrality. In recent years, negative carbon emission technologies have attracted much attention due to their ability to reduce or recycle excess CO2 in the atmosphere. This review summarizes the state-of-the-art negative carbon emission technologies, from the artificial enhancement of natural carbon sink technology to the physical, chemical, or biological methods for carbon capture, as well as CO2 utilization and conversion. Finally, we expound on the challenges and outlook for improving negative carbon emission technology to accelerate the pace of achieving carbon neutrality.

Dye-loaded metal-organic helical capsules applied to the combination of photocatalytic H2S splitting and nitroaromatic hydrogenation

Two dye-loaded metal-organic capsules constructed with different spatial sizes and functional groups simulated the enzymatic substrate activation for hydrogenation of nitroarenes with the kinetics obeying the Michaelis-Menten mechanism.

High Yield of CO and Synchronous S Recovery from the Conversion of CO2 and H2S in Natural Gas Based on a Novel Electrochemical Reactor

H₂S and CO₂ are the main impurities in raw natural gas, which needs to be purified before use. However, the comprehensive utilization of H₂S and CO₂ has been ignored. Herein, we proposed a fully resource-based method to convert toxic gas H₂S and greenhouse gas CO₂ synchronously into CO and elemental S by using a novel electrochemical reactor. The special designs include that, in the anodic chamber, H₂S was oxidized rapidly to S based on the I^-/I₃^- cyclic redox system to avoid anode passivation. On the other hand, in the cathodic chamber, CO₂ was rapidly and selectively reduced to CO based on a porous carbon gas diffusion electrode (GDE) modified with polytetrafluoroethylene and cobalt phthalocyanine (CoPc). A high Faraday efficiency (>95%) toward CO was achieved due to the enhanced mass transfer of CO₂ on the GDE and the presence of the selective CoPc catalyst. The maximum energy efficiency of the system was more than 72.41% with a current density of over 50 mA/cm², which was 12.5 times higher than what was previously reported on the H₂S treatment system. The yields of S and CO were 24.94 mg·cm^-2·h^-1 and 19.93 mL·cm^-2·h^-1, respectively. A model analysis determined that the operation cost of the synchronous utilization of H₂S and CO₂ method was slightly lower than that of the single utilization of H₂S in the existing natural gas purification technology. Overall, this paper provides efficient and simultaneous conversion of H₂S and CO₂ into S and CO.

Van Der Waals gap-rich BiOCl atomic layers realizing efficient, pure-water CO2-to-CO photocatalysis

Photocatalytic CO₂ reduction (PCR) is able to convert solar energy into chemicals, fuels, and feedstocks, but limited by the deficiencies of photocatalysts in steering photon-to-electron conversion and activating CO₂, especially in pure water. Here we report an efficient, pure water CO₂-to-CO conversion photocatalyzed by sub-3-nm-thick BiOCl nanosheets with van der Waals gaps (VDWGs) on the two-dimensional facets, a graphene-analog motif distinct from the majority of previously reported nanosheets usually bearing VDWGs on the lateral facets. Compared with bulk BiOCl, the VDWGs-rich atomic layers possess a weaker excitonic confinement power to decrease exciton binding energy from 137 to 36 meV, consequently yielding a 50-fold enhancement in the bulk charge separation efficiency. Moreover, the VDWGs facilitate the formation of VDWG-Bi-V_O^••-Bi defect, a highly active site to accelerate the CO₂-to-CO transformation via the synchronous optimization of CO₂ activation, *COOH splitting, and *CO desorption. The improvements in both exciton-to-electron and CO₂-to-CO conversions result in a visible light PCR rate of 188.2 μmol g^-1 h^-1 in pure water without any co-catalysts, hole scavengers, or organic solvents. These results suggest that increasing VDWG exposure is a way for designing high-performance solar-fuel generation systems.

Metal-Based Ionic Liquids in Oxidative Desulfurization: A Critical Review

Ionic liquids (ILs) as novel functional desulfurization materials have attracted increasing attentions. Metal-based ionic liquids (MILs) are classified into three types of metal chloride ILs, metal oxide ILs, and metal complex ILs based on the definition and basic structure of MILs in this critical review. On the basis of the properties of ILs such as structure designability, super dissolution performance, good thermal and chemical stability, nonflammability, and wide electrochemical window, MILs exhibit unique advantages on hydrophobicity, oxidation performance, and Brönsted-Lewis acidity. Therefore, MILs possess both the absorption and oxidation centers for the intramolecular adsorption and oxidation to improve the oxidative desulfurization (ODS) process. During the novel nonaqueous wet oxidative desulfurization process (Nasil), H₂S can be oxidized into elemental sulfur with hydrophobic MILs, which can be regenerated by oxygen for recycle, to solve the problems of low sulfur capacity, low sulfur quality, and severe secondary pollution in the aqueous Lo-Cat wet oxidative desulfurization process. Another outstanding feature of MILs in ODS is biomimetic catalysis, which has the function of activating molecular oxygen and improving the oxidation performance. Metal oxide ILs and metal complex ILs are used in combination with hydrogen peroxide or oxygen with the existing water to generate a Fenton-like reaction to convert hydrophobic organic sulfur or SO₂ into hydrophilic sulfoxide/sulfone or sulfur acid, respectively. However, the corrosion of Cl^- to the equipment and emulsification phenomenon in the extraction process of sulfoxide/sulfone separation still need further study. Furthermore, the promising strategies to construct highly efficient and green desulfurization processes for large-scale applications are provided.

Surface Assistant Charge Separation in PEC Cu2S-Ni/Cu2O Cathode

Fabrication of a high efficiency photocathode is a challenging issue in photoelectrocatalysis (PEC). In this work, a Cu₂S-Ni/Cu₂O photocathode was constructed via electrodeposition followed by a two-step overlayer deposition procedure including direct-current magnetron sputtering (DCMS) and ion exchange reaction. We found that the presence of Ni in the inner-layer could not only affect the morphology but also enhance the formation rate of the outer-layer Cu₂S. The XPS results indicate that the Ni exist as NiO_x instead of Ni⁰. The photocurrent of Cu₂S-Ni/Cu₂O achieved 2 times of it on the pristine Cu₂O. The charge dynamic characterizations, including electrochemical impedance spectroscopy (EIS), Tafel slopes, and photoluminescence (PL) spectra, demonstrated that the Ni can promote the hydrogen evolution reaction follow the Heyrovsky reaction, while Cu₂S shows a crucial role on the surface charge separation. At last, surface photovoltage microscopy (SPVM) technology was used to reveal the function of each overlayer. It gives direct evidence for the charge transportation pathway in the system and explains the function of each component.

Efficient conversion of CO2 to methane using thin-layer SiOx matrix anchored nickel catalysts

Thin-layer SiO_x matrix anchored nickel catalysts with high specific surface area and a unique electronic/geometric structure were fabricated for efficient CO₂ methanation.