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Decoration of an axial coordination ligand (ACL) on the active metal site is a highly effective and versatile strategy to tune activity of single‐atom catalysts (SACs). However, the regulation mechanism of ACLs on SACs is still incompletely known. Herein, we investigate diversified combinations of ACL‐SACs, including all 3d–5d transition metals and ten prototype ACLs. We identify that ACLs can weaken the adsorption capability of the metal atom (M) by raising the bonding energy levels of the M−O bond while enhancing dispersity of the d orbital of M. Through examination of various local configurations and intrinsic parameters of ACL‐SACs, a general structure descriptor σ is constructed to quantify the structure–activity relationship of ACL‐SACs which solely based on a few key intrinsic features. Importantly, we also identified the axial ligand descriptor σACL, as a part of σ, which can serve as a potential descriptor to determine the rate‐limiting steps (RLS) of ACL‐SACs in experiment. And we predicted several ACL‐SACs, namely, CrN4‐, FeN4‐, CoN4‐, RuN4‐, RhN4‐, OsN4‐, IrN4‐ and PtN4‐ACLs, that entail markedly higher activities than the benchmark catalysts of Pt and IrO2 for oxygen reduction reaction and oxygen evolution reaction, respectively, thereby supporting that the general descriptor σ can provide a simple and cost‐effective method to assess efficient electrocatalysts. [ABSTRACT FROM AUTHOR]

The existing electronic waste (e‐waste) and leaching solutions generated by industries accumulate significant amounts of gold (Au), even in excess of those in natural minerals. Therefore, the recycling of Au is extremely significant for the potential sustainability of chemical industry. By designing ionic covalent organic frameworks (COFs), here we synthesize a series of Ionic‐COF‐X (X=Cl−, Br−, AcO−, and SO42−) by anion regulation strategy and further explore their adsorption performance towards Au recovery. All these ionic COFs exhibit ultrahigh gold adsorption efficiency and excellent regeneration. Moreover, anion regulation could indeed affect the Au capture performance. In particular, when Cl− ions serve as counter ions, the Au capacity of Ionic‐COF‐Cl could reach 1270.8 mg g−1. Moreover, in the actual CPU leaching solution test, the selectivity of Ionic‐COF‐Cl towards Au3+ ion hits 39000 and 4600 times higher than that of Cu2+ and Ni2+ ions, respectively, suggesting that the Ionic‐COF‐Cl is a promising material for highly selective recovering gold from actual e‐waste. DFT calculations further reveal that counter ions can regulate the adsorption affinity of ionic COF framework toward Au. In short, this work provides a useful anion regulation strategy to design ionic COFs as a promising platform for gold selective recovery from actual e‐waste. [ABSTRACT FROM AUTHOR]

The nickel‐iron based materials are widely studied as excellent oxygen evolution reaction (OER) electrocatalysts. However, its relatively poor OER stability limits its practical applications. Herein, a zipper‐like interlocked heterostructure of NiFe layered double hydroxide (LDH)‐WN is constructed. The NiFe LDH‐WN exhibits not only ultrahigh OER activity of 228 mV overpotential at a current density of 50 mA cm−2, but also extremely long‐term stability over 4500 h at 50 mA cm−2 and over 550 h at an industrial current density ≈350 mA cm−2, which is ascribed to its special zipper‐like interlocked structure. Moreover, in situ Raman confirms that the presence of WN can efficiently achieve NiFe LDH reconstruction to slower the metal dissolution during OER, and therefore boosts its stability. DFT calculations reveal that WN not only can increase the *O adsorption capability and conductivity of NiFe LDH layer, but also can anchor the metal atoms of NiFe LDH layer to improve the dissolution energy barrier. In short, this work presents a new method of constructing the interlocked heterostructure to improve the OER stability of Ni‐Fe‐based catalysts, which would accelerate its practical application. [ABSTRACT FROM AUTHOR]

The semiconducting properties and applications of three dimensional (3D) covalent organic frameworks (COFs) are greatly hampered because of their long‐ranged non‐conjugated skeletons and relatively unstable linkages. Here, a robust imidazole‐linked fully conjugated 3D covalent organic framework (BUCT‐COF‐7) is synthesized through the one‐pot multicomponent Debus‐Radziszewski reaction of the saddle‐shaped aldehyde‐substituted cyclooctatetrathiophene, pyrene‐4,5,9,10‐tetraone, and ammonium acetate. The semiconducting BUCT‐COF‐7, as a metal‐free catalyst, shows excellent two electron oxygen reduction reaction (ORR) activity in alkaline medium with high hydrogen peroxide (H2O2) selectivity of 83.4 %. When the BUCT‐COF‐7 as cathode catalyst is assembled into the electrolyzer, the devices showed high electrochemical production rate of H2O2 up to 326.9 mmol g−1 h−1. The accumulative amount of H2O2 could totally degrade the dye methylene blue via Fenton reaction for wastewater treatment. This is the first report about intrinsic 3D COFs for efficient electrochemical synthesis of H2O2, revealing the promising applications of fully conjugated 3D COFs in the environment‐related field. [ABSTRACT FROM AUTHOR]

Developing low‐cost and high‐efficient bifunctional catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is greatly significant for water electrolysis. Here, Ni3N‐CeO2/NF heterostructure is synthesized on the nickel foam, and it exhibits excellent HER and OER performance. As a result, the water electrolyzer based on Ni3N‐CeO2/NF bifunctional catalyst only needs 1.515 V@10 mA cm−2, significantly better than that of Pt/C||IrO2 catalysts. In situ characterizations unveil that CeO2 plays completely different roles in HER and OER processes. In situ infrared spectroscopy and density functional theory calculations indicate that the introduction of CeO2 can optimizes the structure of interface water, and the synergistic effect of Ni3N and CeO2 improve the HER activity significantly, while the in situ Raman spectra reveal that CeO2 accelerates the reconstruction of OV (oxygen vacancy)‐rich NiOOH for boosting OER. This study clearly unlocks the different catalytic mechanisms of CeO2 for boosting the HER and OER activity of Ni3N for water splitting, which provides the useful guidance for designing the high‐performance bifunctional catalysts for water splitting. [ABSTRACT FROM AUTHOR]

To achieve practical application of fuel cell, it is vital to develop highly efficient and durable Pt‐free catalysts. Herein, we prepare atomically dispersed ZnNC catalysts with Zn‐Pyrrolic‐N4 moieties and abundant mesoporous structure. The ZnNC‐based anion‐exchange membrane fuel cell (AEMFC) presents an ultrahigh peak power density of 1.63 and 0.83 W cm−2 in H2‐O2 and H2‐air (CO2‐free), and also exhibits long‐term stability with more than 120 and 100 h for H2‐air (CO2‐free) and H2‐O2, respectively. Density functional calculations further unveil that the Zn‐Pyrrolic‐N4 structure is the origin of high activity of as‐synthesized ZnNC catalyst, while the Zn‐Pyridinic‐N4 moiety is inactive for oxygen reduction reaction (ORR), which successfully explain the puzzle why most Zn‐metal‐organic framework ‐derived ZnNC catalysts in previous reports did not present good ORR activity because of their Zn‐Pyridinic‐N4 moieties. This work offers a new route for speeding up development of AEMFCs. [ABSTRACT FROM AUTHOR]

The application of three‐dimensional (3D) covalent organic frameworks (COFs) in renewable energy fields is greatly limited due to their non‐conjugated skeletons. Here, we design and successfully synthesize a thiophene‐enriched fully conjugated 3D COF (BUCT‐COF‐11) through an all‐thiophene‐linked saddle‐shaped building block (COThTh‐CHO). The BUCT‐COF‐11 exhibits excellent semiconducting property with intrinsic metal‐free oxygen reduction reaction (ORR) activity. Using the COF as cathode catalyst, the assembled anion‐exchange membrane fuel cells (AEMFCs) exhibited a high peak power density up to 493 mW cm−2. DFT calculations reveal that thiophene introduction in the COF not only improves the conductivity but also optimizes the electronic structure of the sample, which therefore boosts the ORR performance. This is the first report on the application of COFs as metal‐free catalysts in fuel cells, demonstrating the great potential of fully conjugated 3D COFs as promising semiconductors in energy fields. [ABSTRACT FROM AUTHOR]

A general structure descriptor σ is constructed to quantify the structure–activity relationship of axial‐coordination‐ligand single‐atom catalysts (ACL‐SACs), as reported by Dapeng Cao, Xiao Cheng Zeng et al. in their Research Article (e202407812). The σ is solely based on a few key intrinsic features and can provide a simple and quick way to screen efficient electrocatalysts...By Zelong Qiao; Run Jiang; Haoxiang Xu; Dapeng Cao and Xiao Cheng ZengReported by Author; Author; Author; Author; Author [Extracted from the article]

A general structure descriptor σ is constructed to quantify the structure–activity relationship of axial‐coordination‐ligand single‐atom catalysts (ACL‐SACs), as reported by Dapeng Cao, Xiao Cheng Zeng et al. in their Research Article (e202407812). The σ is solely based on a few key intrinsic features and can provide a simple and quick way to screen efficient electrocatalysts...By Zelong Qiao; Run Jiang; Haoxiang Xu; Dapeng Cao and Xiao Cheng ZengReported by Author; Author; Author; Author; Author [Extracted from the article]

Designing highly active multifunctional catalysts to meet the demands for fuel cells, metal–air batteries, and water-splitting devices is a top priority. Here, an efficient and novel trifunctional electrocatalyst (Fe2P/Co@NPC) with Fe2P and Co nanoparticles embedded in porous carbon has been developed by facile one-pot pyrolysis. The synergistic effect of Fe2P and Co nanoparticles furnishes Fe2P/Co@NPC with excellent catalytic performance for oxygen reduction reaction (ORR, E1/2 = 0.876 V), oxygen evolution reaction (OER, η10 = 331 mV), and hydrogen evolution reaction (HER, η10 = 235 mV). Significantly, using Fe2P/Co@NPC catalyst as the cathode, the assembled anion exchange membrane fuel cell delivers a peak power density of 1.25 W cm−2. Moreover, the assembled rechargeable Zn–air battery, using Fe2P/Co@NPC as a bifunctional oxygen catalyst, exhibits a maximum power density of 233.56 mW cm−2 and impressive cycle performance. Using Fe2P/Co@NPC as a bifunctional HER and OER catalyst, the overall water electrolyzer also achieves a low voltage of 1.73 V to deliver 10 mA cm−2. This work represents a protocol for the preparation of high efficient trifunctional electrocatalysts using cheaper heteroatom-containing metal–organic small molecules as a precursor for electrochemical energy devices. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) have recently shown great potential for photocatalytic hydrogen production. Currently almost all reports are focused on two-dimensional (2D) COFs, while the 3D counterparts are rarely explored due to their non-conjugated frameworks derived from the sp 3 carbon based tetrahedral building blocks. Here, we rationally designed and synthesized a series of fully conjugated 3D COFs by using the saddle-shaped cyclooctatetrathiophene derivative as the building block. Through molecular engineering strategies, we thoroughly discussed the influences of key factors including the donor-acceptor structure, hydrophilicity, specific surface areas, as well as the conjugated/non-conjugated structures on their photocatalytic hydrogen evolution properties. The as-synthesized fully conjugated 3D COFs could generate the hydrogen up to 40.36 mmol h -1  g -1 . This is the first report on intrinsic metal-free 3D COFs in photocatalytic hydrogen evolution application. Our work provides insight on the structure design of 3D COFs for highly-efficient photocatalysis, and also reveals that the semiconducting fully conjugated 3D COFs could be a useful platform in clear energy-related fields., (© 2024 Wiley-VCH GmbH.)

The continuous dissolution and oxidation of active sites in Ru-based electrocatalysts have greatly hindered their practical application in proton exchange membrane water electrolyzers (PEMWE). In this work, we first used density functional theory (DFT) to calculate the dissolution energy of Ru in the 3d transition metal-doped MRuO x (M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) to evaluate their stability for acidic oxygen evolution reaction (OER) and screen out ZnRuO x as the best candidate. To confirm the theoretical predictions, we experimentally synthesized these MRuO x materials and found that ZnRuO x indeed displays robust acidic OER stability with a negligible decay of η 10 after 15 000 CV cycles. Of importance, using ZnRuO x as the anode, the PEMWE can run stably for 120 h at 200 mA cm -2 . We also further uncover the stability mechanism of ZnRuO x , i.e., Zn atoms doped in the outside of ZnRuO x nanocrystal would form a "Zn-rich" shell, which effectively shortened average Ru-O bond lengths in ZnRuO x to strengthen the Ru-O interaction and therefore boosted intrinsic stability of ZnRuO x in acidic OER. In short, this work not only provides a new study paradigm of using DFT calculations to guide the experimental synthesis but also offers a proof-of-concept with 3d metal dopants as RuO 2 stabilizer as a universal principle to develop high-durability Ru-based catalysts for PEMWE.

Designing robust bifunctional catalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction in all-pH conditions for overall water splitting (OWS) is an effective way to achieve sustainable development. Herein, a composite Ru-VO 2 containing Ru-doped VO 2 and Ru nanoparticles (NPs) is synthesized, and it shows a high OWS performance in full-pH range due to their synergist effect. In particular, the OER mass activities of Ru-VO 2 at 1.53 V (vs RHE) in acidic, alkaline, and PBS solutions are ≈65, 36, and 235 times of commercial RuO 2 in the same conditions. The "Ru-VO 2 || Ru-VO 2 " two-electrode electrolyzer only needs a voltage of 1.515 V (at 10 mA cm -2 ) in acidic water splitting, which can operate stably for 125 h at 10 mA cm -2 without significant voltage decay. In situ Raman spectra and in situ differential electrochemical mass spectrometry prove that the OER of Ru-VO 2 in acid follows the adsorption evolution mechanism. Density functional theory calculations further reveal the synergistic effect between Ru NP and Ru-doped VO 2 , which breaks the hydrogen bond network formed by *OH adsorbed on the Ru single-atom site, and thereby significantly enhances the OER activity. This work provides new insights into the design of novel bifunctional pH-universal catalysts for OWS., (© 2023 Wiley-VCH GmbH.)

Discovering highly efficient and stable non-precious metal catalysts for the oxygen evolution reaction (OER) is crucial for energy conversion in water splitting. However, preparing high-performance OER catalysts and elucidating the structural changes in the process are still challenging. Herein, we synthesize the NiTe/Ni 2 P heterostructure and demonstrate the strain engineering of NiTe/Ni 2 P via the lattice incompatibility between the phosphide and the telluride. The strain engineering of the NiTe/Ni 2 P heterostructure not only significantly boosts the OER activity but also effectively stabilizes the intrinsic structure of the catalyst after the OER process by using the in situ -produced metal salt as a protection layer. After the OER stability test, no oxyhydroxide phase is observed, and in situ Raman spectroscopy reveals that a voltage-dependent phase transition appears during the OER, which is different from most previously reported Ni-based catalysts, for which the generation of irreversible NiOOH occurs after the OER. Density functional theory calculations further reveal that the tensile strain of Ni 2 P will inhibit the presence of irreversible phase transitions of Ni 2 P into NiOOH due to the weak adsorption ability of the oxygen species caused by strain engineering. In short, this work opens a new gate for using strain nanotechnology to design high-performance OER catalysts.

To achieve practical application of fuel cell, it is vital to develop highly efficient and durable Pt-free catalysts. Herein, we prepare atomically dispersed ZnNC catalysts with Zn-Pyrrolic-N 4 moieties and abundant mesoporous structure. The ZnNC-based anion-exchange membrane fuel cell (AEMFC) presents an ultrahigh peak power density of 1.63 and 0.83 W cm -2 in H 2 -O 2 and H 2 -air (CO 2 -free), and also exhibits long-term stability with more than 120 and 100 h for H 2 -air (CO 2 -free) and H 2 -O 2 , respectively. Density functional calculations further unveil that the Zn-Pyrrolic-N 4 structure is the origin of high activity of as-synthesized ZnNC catalyst, while the Zn-Pyridinic-N 4 moiety is inactive for oxygen reduction reaction (ORR), which successfully explain the puzzle why most Zn-metal-organic framework -derived ZnNC catalysts in previous reports did not present good ORR activity because of their Zn-Pyridinic-N 4 moieties. This work offers a new route for speeding up development of AEMFCs., (© 2022 Wiley-VCH GmbH.)