Size‐Dependent Activity and Selectivity of Atomic‐Level Copper Nanoclusters during CO/CO 2 Electroreduction

TM2 -B2 Quadruple Active Sites Supported on a Defective C3 N Monolayer as Catalyst for the Electrochemical CO2 Reduction: A Theoretical Perspective

Developing high-performance electrocatalysts for the CO₂ reduction reaction (CO₂ RR) holds great potential to mitigate the depletion of fossil feedstocks and abate the emission of CO₂ . In this contribution, using density functional theory calculations, we systematically investigated the CO₂ RR performance catalyzed by TM₂ -B₂ (TM=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu) supported on a defective C₃ N monolayer (V-C₃ N). Through the screening in terms of stability of catalyst, activity towards CO₂ adsorption, and selectivity against hydrogen evolution reaction, Mn₂ -, Fe₂ -, Co₂ -, and Ni₂ -B₂ @V-C₃ N were demonstrated to be a highly promising CO₂ RR electrocatalyst. Due to quadruple active sites, these candidates can adsorb two or three CO₂ molecules. Strikingly, different products, distributing from C₁ to C₂₊ , can be generated. The high activity originates from the synergistic effect of TM and B atoms, in which they serve as adsorption sites for the C- and O-species, respectively. The high selectivity towards C₂₊ products at the Fe₂ -, and Ni₂ -B₂ sites stems from moderate C adsorption strength but relatively weak O adsorption strength, in which a universal descriptor, that is, 0.6 ΔE_C -0.4 ΔE_O =-1.77 eV (ΔE_C /ΔE_O is the adsorption energy of C/O), was proposed. This work would offer a novel perspective for the design of high active electrocatalysts towards CO₂ RR and for the synthesis of C₂₊ compounds.

Second Sphere Effects Promote Formic Acid Dehydrogenation by a Single-Atom Gold Catalyst Supported on Amino-Substituted Graphdiyne

Regulating the second sphere of homogeneous molecular catalysts is a common and effective method to boost their catalytic activities, while the second sphere effects have rarely been investigated for heterogeneous single-atom catalysts primarily due to the synthetic challenge for installing functional groups in their second spheres. Benefiting from the well-defined and readily tailorable structure of graphdiyne (GDY), an Au single-atom catalyst on amino-substituted GDY is constructed, where the amino group is located in the second sphere of the Au center. The Au atoms on amino-decorated GDY displayed superior activity for formic acid dehydrogenation compared with those on unfunctionalized GDY. The experimental studies, particularly the proton inventory studies, and theoretical calculations revealed that the amino groups adjacent to an Au atom could serve as proton relays and thus facilitate the protonation of an intermediate Au-H to generate H₂ . Our study paves the way to precisely constructing the functional second sphere on single-atom catalysts.

Electronic Perturbation of Copper Single-Atom CO2 Reduction Catalysts in a Molecular Way

Fine-tuning electronic structures of single-atom catalysts (SACs) plays a crucial role in harnessing their catalytic activities, yet challenges remain at a molecular scale in a controlled fashion. By tailoring the structure of graphdiyne (GDY) with electron-withdrawing/-donating groups, we show herein the electronic perturbation of Cu single-atom CO₂ reduction catalysts in a molecular way. The elaborately introduced functional groups (-F, -H and -OMe) can regulate the valance state of Cu^δ+ , which is found to be directly scaled with the selectivity of the electrochemical CO₂ -to-CH₄ conversion. An optimum CH₄ Faradaic efficiency of 72.3 % was achieved over the Cu SAC on the F-substituted GDY. In situ spectroscopic studies and theoretical calculations revealed that the positive Cu^δ+ centers adjusted by the electron-withdrawing group decrease the pK_a of adsorbed H₂ O, promoting the hydrogenation of intermediates toward the CH₄ production. Our strategy paves the way for precise electronic perturbation of SACs toward efficient electrocatalysis.

Graphdiyne-Based Single-Atom Catalysts with Different Coordination Environments

As a special carbon material, graphdiyne (GDY) features the superiorities of incomplete charge transfer effect on the atomic level, tunable electronic structure and anchoring metal atoms directly with organometallic coordination bonds M (metal)-C (alkynyl carbon in GDY), providing it an ideal platform to construct single-atom catalysts (ACs). The coordination environment of single atoms anchored on GDY plays a key role in their catalytic performance. The mini-review highlights state-of-the-art progress in the rational design of GDY-based ACs and their applications, and mainly reveals the relationship between the coordination engineering of the GDY-based ACs and corresponding catalytic performance. Finally, some prospects concerning the future development of GDY-based ACs in energy conversion are also discussed.

A Deprotection-free Method for High-yield Synthesis of Graphdiyne Powder with In Situ Formed CuO Nanoparticles

With a direct band gap, superior charge carrier mobility, and uniformly distributed pores, graphdiyne (GDY) has stimulated tremendous interest from the scientific community. However, its broad application is greatly limited by the complicated multistep synthesis process including complex deprotection of hexakis-[(trimethylsilyl)ethynyl]benzene (HEB-TMS) and peeling of GDY from the substrates. Here, we describe a deprotection-free strategy to prepare GDY powder by directly using HEB-TMS as the monomer. When CuCl was used as the catalysts in DMF solvent, the yield of GDY powder reached ≈100 %. More interestingly, uniformly dispersed CuO nanoparticles with an average diameter of ≈2.9 nm were in situ formed on GDY after the reaction. The prepared CuO/GDY was demonstrated an excellent co-catalyst for photocatalytic hydrogen evolution, comparable to the state-of-art Pt co-catalyst. The deprotection-free approach will widen the use of GDY and facilitate its scaling up to industrial level.