Yanfang Gao

Developing effective electrocatalysts that can convert low-concentration nitrate (NO3–) into ammonia (NH3) in dilute electrolytes remains a major challenge. In this work, high-performance atomically dispersed CuCo catalysts (CuCo-ADCs) were prepared using a hydrothermal route. When tested in electrolyte containing 50 ppm NO3–-N and 5 mM K2SO4 (supporting electrolyte), the catalyst delivered a high NH3 Faradaic efficiency (FE) of 92.15%, ammonia selectivity of 96.33%, and NH3 production rate of 281.28 μg h–1 cm–2 at –0.6 V vs reversible hydrogen electrode (RHE). Electrochemical measurements indicated reduced solution diffusion resistance for this catalyst. After 10 h of continuous operation, more than 85% of the initial catalytic activity could be retained. Mechanistic characterizations suggested that the atomic-level dispersion accelerated reaction kinetics and suppressed the competing hydrogen evolution reaction. Such improvement originated from the optimized *NO3 adsorption and decreased N═O bond dissociation energy through bimetallic synergy. Within this catalytic system, Cu drove the nitrate reduction reaction, Co was responsible for key bond cleavage, and Ni promoted hydrogenation steps as well as product desorption. This study offers alternative design ideas for atomically dispersed catalysts intended for resource recovery from low-concentration nitrate-rich wastewater. The present catalytic system may be applied for simultaneous nitrogen removal and ammonia generation in practical wastewater treatment.

In solid-state lithium metal batteries (SSLMBs), the development of high-performance solid-state electrolytes (SSEs) hinges on materials that can simultaneously enable rapid lithium-ion transport and suppress dendrite growth. Hydrogen-bonded organic frameworks (HOFs) based on diamino-triazine moieties offer a promising solution to these challenges, leveraging their unique structural attributes: the electron-rich triazine rings form planar hydrogen-bond networks that provide directional pathways for lithium-ion migration, while terminal -NH2 groups act as lithium-ion coordination sites to enhance lithium-ion dissociation and suppress anion mobility within the HOF channels, thereby improving Li+ conduction. Three diamino-triazine HOFs (HOF-MA-1, -2, -3) were synthesized via hydrothermal assembly of melamine with various synthon linkers, resulting in network structures rich in hydrogen bonds. When employed as solid-state electrolytes, the HOF-MA-3 electrolyte membrane exhibits exceptional performance: a room-temperature Li+ conductivity of 2.66×10-3 S cm-1, a high Li+ transference number of 0.89, and a wide electrochemical window of 0.1–4.8 V. These favorable properties enable stable cycling of SSLMBs, with a capacity retention as a high capacity retention of 89% after 100 cycles at 1 C. This remarkable cycling stability can be attributed to the HOF's intrinsic ability to promote the formation of a stable solid-electrolyte interphase and its provision of continuous ion-conducting pathways.

Manganese dioxide (MnO2) stands out as a promising multifunctional material for supercapacitors and hydrogen evolution reaction (HER) owing to its high theoretical capacitance, rich valence states, low cost, and environmental friendliness. However, the strong Jahn-Teller effect induces electron localization in Mn3+, giving rise to poor intrinsic conductivity, sluggish charge transport, and structural instability, which severely restricts its practical applications. Herein, a series of Zn-doped MnO2 was synthesized through a facile hydrothermal method to modulate the spin state and electronic structure of MnO2. Zn doping triggered local lattice distortion, broke the symmetric octahedral field of [MnO6], and optimized the occupation of Mn 3d orbitals, thereby enhancing spin polarization and promoting d-electron delocalization. Systematic characterizations and density functional theory (DFT) calculations verified that Zn doping reduced the bandgap of MnO2 from 1.7 eV to 1.1 eV, increased the eg orbital occupancy, and generated abundant oxygen vacancies and electrochemically active sites, which significantly improved electron mobility and ion diffusion kinetics. As the supercapacitor cathode, the assembled Zn-MnO2//La-MoO3/GQDs asymmetric supercapacitor achieved a maximum energy density of 23.9 Wh kg−1 with 80.9% capacitance retention after 6000 cycles. Meanwhile, as an electrocatalyst for HER in 1 M KOH, 1% Zn-MnO2 exhibited a lower overpotential of 161 mV at 10 mA cm−2 and a small Tafel slope of 85 mV dec−1, with outstanding stability after 5000 cycles. This work demonstrated that Zn doping-induced spin state modulation effectively addressed the inherent limitations of MnO2, providing a feasible strategy for designing high-performance Mn-based materials for integrated energy storage and conversion applications.

Advancing cost-effective and efficient Fe–N–C catalysts is essential for expanding the commercial viability of Zn–air batteries. Covalent organic frameworks (COFs) have emerged as promising precursors owing to their tunable architecture and excellent chemical stability. However, their limited electrochemical activity and harsh synthesis conditions have hindered practical applications. In this work, macromolecular polyimide COFs (PI-COFs) were successfully synthesized through a high-temperature solid-phase method. The π-conjugation degree of the xCN/Fe catalysts was finely tuned by adjusting the size of the imide π-conjugation unit within the PI-COF framework. Structural characterization confirmed that variations in π-conjugation directly affected the density of delocalized π electrons. A volcano-type dependence was observed between π-electron delocalization and OER activity. Notably, the MNCN/Fe catalyst with moderate π conjugation demonstrated excellent bifunctional activity, with an ORR half-wave potential of 0.808 V (vs. RHE) and an OER overpotential of 322 mV at 10 mA cm⁻². The MNCN/Fe-based Zn–air battery could illuminate a small light bulb, verifying its practical feasibility. Overall, this work establishes an effective strategy to modulate π-conjugation in Fe–N–C catalysts for enhanced electrochemical energy conversion.

Defect-rich Ni-TDC nanoflowers by Fe( iii ) ions substitution at Ni2 sites have great potential for assembling high-performance energy storage devices.

Layered manganese dioxide (δ-MnO₂) exhibits potential in the hydrogen evolution reaction (HER) due to its multivalent redox properties and high specific surface area. However, its poor intrinsic conductivity and insufficient active sites limit the electron transfer efficiency and adsorption/desorption of *H intermediates. Herein, we constructed an X–MO/NF (X = Ni, Cu, Zn) electrocatalytic system by in situ growth of δ-MnO₂ on the surface of nickel foam (NF) via a one-step hydrothermal method and introduction of transition metal atoms. It has been shown that the transition metals trigger the charge compensation mechanism by changing the O coordination environment, inducing the formation of oxygen vacancies and unsaturated Mn³⁺ sites in MnO₂ lattice, thus balancing the charge distribution and optimizing the electronic structure. Ni–MO/NF, Cu–MO/NF, and Zn–MO/NF exhibit low overpotentials of 145 mV, 131 mV, and 115 mV at 10 mA cm⁻² in 1 M KOH, respectively. Theoretical calculations confirmed that via Ni, Cu, and Zn doping, the hydrogen adsorption-free energy could be reduced and the surface reaction kinetics accelerated. Nevertheless, the diversity of their orbital contributions to the electronic structure of MnO₂ led to different redistributions of the electron cloud density, thus showing variation in the degree of enhancement of the catalytic performance. This work reveals the regulation rule of transition metal atoms on the coordination environment of δ-MnO₂, which provides a new perspective and theoretical guidance for optimizing the catalytic performance of transition metal oxides.

The development of cost-effective and straightforward methodologies for the fabrication of high-performance electrode materials represents a crucial advancement in the application and evolution of supercapacitors (SCs). Hierarchical porous carbon materials have been considered a type of promising material for SCs owing to their high specific surface area and excellent electronic conductivity. Herein, the synthesis of structurally controllable porous carbons from pomelo peel through carbonization, the template method and activation treatment is reported. In this work, an impedance model was used to evaluate the charge storage capacity and ion transmission rate of porous electrodes of SCs. Biochar materials were prepared using CaCO₃ and KOH as the template and activator, respectively, and the effects of different template and activator contents on the specific surface area, pore volume, morphology and electrochemical properties of the prepared biochar materials were investigated. The as-prepared biochar, designated as 800-PAC-750-1:1, possessed a hierarchically porous framework with a relatively high specific surface area of 2384 m² g⁻¹ and a specific capacitance of 240.3 F g⁻¹ at a current density of 0.5 A g⁻¹. The 800-PAC-750-1:1 electrode also exhibited excellent cycling stability with 87.5% capacitance retention after 10 000 cycles.

In situ formation of VN quantum nanodots (VNQDs) anchored on a three-dimensional porous N-doped carbon (PNC) skeleton was achieved by a simple strategy to build porous VNQDs@PNC composites as pseudocapacitive anode materials for LIBs.