Near-Equilibrium Growth of Chemically Stable Covalent Organic Framework/Graphene Oxide Hybrid Materials for the Hydrogen Evolution Reaction

Designable Photo-Responsive Micron-Scale Ultrathin Peptoid Nanobelts for Enhanced Performance on Hydrogen Evolution Reaction

The development of high-reactive single-atom catalysts (SACs) based on long-range-ordered ultrathin organic nanomaterials (UTONMs) (i.e., below 3 nm) provides a significant tactic for the advancement in hydrogen evolution reactions (HER) but remains challenging. Herein, photo-responsive ultrathin peptoid nanobelts (UTPNBs) with a thickness of ≈2.2 nm and micron-scaled length are generated using the self-assembly of azobenzene-containing amphiphilic ternary alternating peptoids. The pendants hydrophobic conjugate stacking mechanism reveals the formation of 1D ultralong UTPNBs, whose thickness is dictated by the length of side groups that are linked to peptoid backbones. The photo-responsive feature is demonstrated by a reversible morphological transformation from UTPNBs to nanospheres (21.5 nm) upon alternative irradiation with UV and visible lights. Furthermore, the electrocatalyst performance of these aggregates co-decorated with nitrogen-rich ligand of terpyridine (TE) and uniformly-distributed atomic platinum (Pt) is evaluated toward HER, with a photo-controllable electrocatalyst activity that highly depended on both the presence of Pt element and structural characteristic of substrates. The Pt-based SACs using TE-modified UTPNBs as support exhibit a favorable electrocatalytic capacity with an overpotential of ≈28 mV at a current density of 10 mA cm-2. This work presents a promising strategy to fabricate stimuli-responsive UTONMs-based catalysts with controllable HER catalytic performance.

COF-Based Photocatalysts for Enhanced Synthesis of Hydrogen Peroxide

Covalent Organic Frameworks (COFs), with their intrinsic structural regularity and modifiable chemical functionality, have burgeoned as a pivotal material in the realm of photocatalytic hydrogen peroxide (H2O2) synthesis. This article reviews the recent advancements and multifaceted approaches employed in using the unique properties of COFs for high-efficient photocatalytic H2O2 production. We first introduced COFs and their advantages in the photocatalytic synthesis of H2O2. Subsequently, we spotlight the principles and evaluation of photocatalytic H2O2 generation, followed by various strategies for the incorporation of active sites aiming to optimize the separation and transfer of photoinduced charge carriers. Finally, we explore the challenges and future prospects, emphasizing the necessity for a deeper mechanistic understanding and the development of scalable and economically viable COF-based photocatalysts for sustainable H2O2 production.

Engineering organic polymers as emerging sustainable materials for powerful electrocatalysts

Cost-effective and high-efficiency catalysts play a central role in various sustainable electrochemical energy conversion technologies that are being developed to generate clean energy while reducing carbon emissions, such as fuel cells, metal-air batteries, water electrolyzers, and carbon dioxide conversion. In this context, a recent climax in the exploitation of advanced earth-abundant catalysts has been witnessed for diverse electrochemical reactions involved in the above mentioned sustainable pathways. In particular, polymer catalysts have garnered considerable interest and achieved substantial progress very recently, mainly owing to their pyrolysis-free synthesis, highly tunable molecular composition and microarchitecture, readily adjustable electrical conductivity, and high stability. In this review, we present a timely and comprehensive overview of the latest advances in organic polymers as emerging materials for powerful electrocatalysts. First, we present the general principles for the design of polymer catalysts in terms of catalytic activity, electrical conductivity, mass transfer, and stability. Then, the state-of-the-art engineering strategies to tailor the polymer catalysts at both molecular (i.e., heteroatom and metal atom engineering) and macromolecular (i.e., chain, topology, and composition engineering) levels are introduced. Particular attention is paid to the insightful understanding of structure-performance correlations and electrocatalytic mechanisms. The fundamentals behind these critical electrochemical reactions, including the oxygen reduction reaction, hydrogen evolution reaction, CO2 reduction reaction, oxygen evolution reaction, and hydrogen oxidation reaction, as well as breakthroughs in polymer catalysts, are outlined as well. Finally, we further discuss the current challenges and suggest new opportunities for the rational design of advanced polymer catalysts. By presenting the progress, engineering strategies, insightful understandings, challenges, and perspectives, we hope this review can provide valuable guidelines for the future development of polymer catalysts.

Single Ru Sites on Covalent Organic Framework-Coated Carbon Nanotubes for Highly Efficient Electrocatalytic Hydrogen Evolution

Covalent organic frameworks (COFs) with precisely controllable structures and highly ordered porosity possess great potential as electrocatalysts for hydrogen evolution reaction (HER). However, the catalytic performance of pristine COFs is limited by the poor active sites and low electron transfer. Herein, to address these issues, the conductive carbon nanotubes (CNTs) are coated by a defined structure RuBpy(H2 O)(OH)Cl2 in bipyridine-based COF (TpBpy). And this composite with single site Ru incorporated can be used as HER electrocatalyst in alkaline conditions. A series of crucial issues are carefully discussed through experiments and density functional theory (DFT) calculations, such as the coordination structure of the atomically dispersion Ru ions, the catalytic mechanism of the embedded catalytic site, and the effect of COF and CNTs on the electrocatalytic properties. According to DFT calculations, the embedded single sites Ru act as catalytic sites for H2 generation. Benefitting from increasing the catalyst conductivity and the charge transfer, the as-prepared c-CNT-0.68@TpBpy-Ru shows an excellent HER overpotential of 112 mV at 10 mA cm-2 under alkaline conditions as well as an excellent durability up to 12 h, which is superior to that of most of the reported COFs electrocatalysts in alkaline solution.

Single Cobalt Atoms Immobilized on Palladium-Based Nanosheets as 2D Single-Atom Alloy for Efficient Hydrogen Evolution Reaction

Single-atom alloys (SAAs) display excellent electrocatalytic performance by overcoming the scaling relationships in alloys. However, due to the lack of a unique structure engineering design, it is difficult to obtain SAAs with a high specific surface area to expose more active sites. Herein, single Co atoms are immobilized on Pd metallene (Pdm) support to obtain Co/Pdm through the design of the engineered morphology of Pd, realizing the preparation of ultra-thin 2D SAA. The unsaturated coordination environments combined with the unique geometric and electronic structures realize the modulation of the d-band center and the redistribution of charges, generating highly active electronic states on the surface of Co/Pdm. Benefiting from the synergistic interaction and spillover effect, the Co/Pdm electrocatalyst exhibits outstanding hydrogen evolution reaction (HER) performance in both acid and alkaline solutions, especially with a Tafel slope of 8.2 mV dec^-1 and a low overpotential of 24.7 mV at 10 mA cm^-2 in the acidic medium, which outperforms commercial Pt/C and Pd/C. This work highlights the successful preparation of 2D ultra-thin SAA, which provides a new strategy for the preparation of HER electrocatalyst with high efficiency, activity, and stability.

Ultrathin 2D Cerium-Based Metal-Organic Framework Nanosheet That Boosts Selective Oxidation of Inert C(sp3 )H Bond through Multiphoton Excitation

The development of methodologies for inducing and tailoring activities of catalysts is an important issue in various catalysis. The ultrathin 2D monolayer metal-organic framework (MOF) nanosheets with more accessible active sites and faster diffusion obtained by exfoliating 3D layered MOFs are of great potential as heterogeneous catalysts, but the rational design and preparation of 3D layered MOFs remains a grand challenge. Herein, a novel weak electrostatic interaction strategy to construct a 3D layered cerium-bearing MOF by coordinating chlorine-capped cerium nodes and linear photoactive methyl viologen (MV⁺ ) organic linkers is used. Under multiphoton excitation, the MV⁺ ligands and CeCl chromophores are triggered consecutively to form the high activity chlorine radical (Cl^• ) for activation of inert C(sp³ )H bond through a hydrogen atom transfer. Benefiting from framework confinement effects, synergistic effects of two active sites and/or flexibility of the ultrathin framework nanosheets with high surface utilization, the observed activities increase in the order CeCl₃ /MV⁺  < bulk 3D MOF crystals < 2D MOF nanosheets in photocatalysis. This work not only contributes a new strategy to construct 3D layered MOFs and their ultrathin nanosheets but also paves the way to use nanostructured MOFs to handle synergy of multiple molecular catalysts.