A Carbon-Negative Hydrogen Production Strategy: CO2 Selective Capture with H2 Production

Efficient Fe3O4/Fe Redox Cycle with Biomass Waste Glycerol for Net Carbon Benefit CO2 Reduction

CO2 utilization is a critical aspect of achieving a sustainable carbon cycle, particularly in the context of global efforts to achieve carbon neutrality. Drawing inspiration from geological chemistry, Fe-based hydrothermal CO2 reduction into valuable chemicals has emerged as a promising CO2 utilization strategy. However, the lack of a sustainable and direct Fe regeneration approach presents a notable challenge to the widespread adoption of this strategy. Herein, we propose a method for the direct reduction of Fe3O4 to Fe using biodiesel-waste glycerol. This method yields a remarkable 97.9 wt % of reduced Fe, which exhibits a high activity for CO2 (HCO3 -) reduction to formic acid, maintaining a level of ~90 %. Our investigation reveals that the Fe3O4 reduction involves a direct hydrogen transfer from hydroxyl groups to lattice O atoms on the surface of Fe3O4, forming reductive H species. The presence of a polyhydroxy structure in glycerol facilitates the stabilization of surface H species, thereby enhancing the reduction efficiency process. Based on this mechanism, we explore the potential of using various polyols derived from woody biomass, which exhibit similar capabilities for the reduction of Fe3O4 as glycerol. These findings establish an efficient and sustainable Fe3O4/Fe redox cycle, which integrates waste biomass into circular carbon economy solutions and contributes to the overall net carbon benefit of CO2 utilization.

Efficient photoreduction of CO2 to CO by Co-ZIL-L derived NiCo-OH with ultrathin nanosheet assembled 2D leaf superstructure

The photocatalytic reduction of CO2 into valuable chemicals and fuels is considered a promising solution to address the energy crisis and environmental challenges. In this work, we introduce a Co-ZIL-L mediated in situ etching and integration process to prepare NiCo-OH with an ultrathin nanosheet-assembled 2D leaf-like superstructure (NiCo-OH UNLS). The resulting catalyst demonstrates excellent photocatalytic performance for CO2 reduction, achieving a CO evolution rate as high as 309.5 mmol g-1 h-1 with a selectivity of 91.0%. Systematic studies reveal that the ultrathin nanosheet structure and 2D leaf-like architecture not only enhance the transfer efficiency of photoexcited electrons but also improve the accessibility of active reaction sites. Additionally, the Ni-Co dual sites in NiCo-OH UNLS accelerate CO2 conversion kinetics by stabilizing the *COOH intermediate, significantly contributing to its high activity. This work offers valuable insights for designing advanced photocatalysts for CO2 conversion.

Bifunctional PdMoPt trimetallene boosts alcohol-water electrolysis

Substituting oxygen evolution with alcohol oxidation is crucial for enhancing the cathodic hydrogen evolution reaction (HER) at low voltages. However, the development of high-performance bifunctional catalysts remains a challenge. In this study, an ultrathin and porous PdMoPt trimetallene is developed using a wet-chemical strategy. The synergetic effect between alloying metals regulates the adsorption energy of reaction intermediates, resulting in exceptional activity and stability for the electrooxidation of various alcohols. Specifically, the mass activity of PdMoPt trimetallene toward the electrooxidation of methanol, ethylene glycol, and glycerol reaches 6.13, 5.5, and 4.37 A mgPd+Pt -1, respectively. Moreover, the catalyst demonstrates outstanding HER activity, requiring only a 39 mV overpotential to achieve 10 mA cm-2. By employing PdMoPt trimetallene as both the anode and cathode catalyst, we established an alcohol-water hybrid electrolysis system, significantly reducing the voltage requirements for hydrogen production. This work presents a promising avenue for the development of bifunctional catalysts for energy-efficient hydrogen production.

Ruthenium Single Atomic Sites Surrounding the Support Pit with Exceptional Photocatalytic Activity

Single-metal atomic sites and vacancies can accelerate the transfer of photogenerated electrons and enhance photocatalytic performance in photocatalysis. In this study, a series of nickel hydroxide nanoboards (Ni(OH)x NBs) with different loadings of single-atomic Ru sites (w-SA-Ru/Ni(OH)x) were synthesized via a photoreduction strategy. In such catalysts, single-atomic Ru sites are anchored to the vacancies surrounding the pits. Notably, the SA-Ru/Ni(OH)x with 0.60 wt % Ru loading (0.60-SA-Ru/Ni(OH)x) exhibits the highest catalytic performance (27.6 mmol g-1 h-1) during the photocatalytic reduction of CO2 (CO2RR). Either superfluous (0.64 wt %, 18.9 mmol g-1 h-1; 3.35 wt %, 9.4 mmol-1 h-1) or scarce (0.06 wt %, 15.8 mmol g-1 h-1; 0.29 wt %, 21.95 mmol g-1 h-1; 0.58 wt %, 23.4 mmol g-1 h-1) of Ru sites have negative effect on its catalytic properties. Density functional theory (DFT) calculations combined with experimental results revealed that CO2 can be adsorbed in the pits; single-atomic Ru sites can help with the conversion of as-adsorbed CO2 and lower the energy of *COOH formation accelerating the reaction; the excessive single-atomic Ru sites occupy vacancies that retard the completion of CO2RR.

π-Sticked Metal‒Organic Monolayers for Single-Metal-Site Dependent CO2 Photoreduction and Hydrogen Evolution Reaction

Hierarchical self-assembly of 2D metal‒organic layers (MOLs) for the construction of advanced functional materials have witnessed considerable interest, due to the increasing atomic utilizations and well-defined atom‒property relationship. However, the construction of atomically precise MOLs with mono-/few-layered thickness through hierarchical self-assembly process remains a challenge, mostly because the elaborate long-range order is difficult to control via conventional noncovalent interaction. Herein, a quadruple π-sticked metal‒organic layer (πMOL) is reported with checkerboard-like lattice in ≈1.0 nanometre thickness, on which the catalytic selectivity can be manipulated for highly efficient CO2 reduction reaction (CO2RR) and hydrogen evolution reaction (HER) over a single metal site. In saturated CO2 aqueous acetonitrile, Fe-πMOL achieves a highly effective CO2RR with the yield of ≈3.98 mmol g‒1 h‒1 and 91.7% selectivity. In contrast, the isostructural Co-πMOL as well as mixed metallic FeCo-πMOL exhibits a high activity toward HER under similar conditions. DFT calculations reveal that single metal site exhibits the significant difference in CO2 adsorption energy and activation barrier, which triggers highly selective CO2RR for Fe site and HER for Co site, respectively. This work highlights the potential of supramolecular π…π interaction for constructing monolayer MOL materials to uniformly distribute the single metal sites for artificial photosynthesis.

Electrocatalysis Boosts the Methanol Thermocatalytic Dehydrogenation for High-Purity H2 and CO Production

Hydrogen production from methanol represents an energy-sustainable way to produce ethanol, but it normally results in heavy CO2 emissions. The selective conversion of methanol into H2 and valuable chemical feedstocks offers a promising strategy; however, it is limited by the harsh operating conditions and low conversion efficiency. Herein, we realize efficient high-purity H2 and CO production from methanol by coupling the thermocatalytic methanol dehydrogenation with electrocatalytic hydrogen oxidation on a bifunctional Ru/C catalyst. Electrocatalysis enables the acceleration of C-H cleavage and reduces the partial pressure of hydrogen at the anode, which drives the chemical equilibrium and significantly enhances methanol dehydrogenation. Furthermore, a bilayer Ru/C + Pd/C electrode is designed to mitigate CO poisoning and facilitate hydrogen oxidation. As a result, a high yield of H2 (558.54 mmol h-1 g-1) with high purity (99.9%) was achieved by integrating an applied cell voltage of 0.4 V at 200 °C, superior to the conventional thermal and electrocatalytic processes, and CO is the main product at the anode. This work presents a new avenue for efficient H2 production together with valuable chemical synthesis from methanol.

Regulating Degradation Pathways of Polymers by Radical-Triggered Luminescence

Understanding the radical behaviours during polymer degradation is beneficial to unveil and regulate the degradation pathways of polymers to achieve a sustainable polymer development. However, it is a long-standing challenge to study radical behaviours owing to the ultra-short lifetime of the transient radicals generated during the polymer degradation. In this contribution, we have proposed the radical-triggered luminescence to monitor the radical behaviours during polymer degradation without/with the addition of inorganic additives. It was disclosed that the pure polymers showed a single sigmoidal dynamic curve from peroxy radicals (ROO⋅) emissions, leading to the exponential proliferation for the degradation evolution. Alternatively, the degradation pathways with the addition of additives, layered double hydroxides (LDHs) with positively charged Al centers, could be modulated into a double sigmoidal dynamics, involving the main product of alkoxy radicals (RO⋅) with the activation energy of 40.2 kJ/mol and a small amount of ROO⋅ with 76.3 kJ/mol, respectively. Accordingly, the polymers with the additive-regulated pathways could exhibit prominently anti-degradation behaviours. This work is beneficial for the deep understanding of the radical mechanisms during polymer degradation, and for the rational design of anti-degradation polymers.