Haijun Liu

The chemical stability of cationic groups, not only related to alkaline degradation but also to electrochemical degradation at high potentials, is the key factor that limits the durability of anion exchange membranes (AEMs) and anion exchange ionomers (AEIs) [1]. In recent years, quaternary ammonium (QA) groups represented by N-heterocyclic ammonium (NHA) groups display excellent ionic conductivity and superior alkaline stability, which makes NHA groups promising candidates to be applied in AEMs and AEIs [2]. However, electrochemical degradation of NHA groups has been neglected in previous research, even though the electrochemical oxidation of phenyl QAs was found in the ionomer at the oxygen evolution potentials [3]. In short, the mechanism by which effect of substituents affects the durability of NHAs cations, including alkaline stability and electrochemical stability, is unclear yet, and NHA groups must be attached to the polymer backbones by substituents to achieve their applications. In this work, the chemical stability of NHA is comprehensively studied. To investigate the relationship between alkaline durability and structure, we report a systematic study on the alkaline stability of 24 representative NHA groups at different hydration numbers (λ). The electronic effect of substituents on NHA groups and degradation mechanisms of NHA groups are systematically investigated by ¹H nuclear magnetic resonance (¹H NMR) and density functional theory (DFT) calculations, showing that the NHA groups with electron-donating substituents exhibit outstanding alkaline stability and linking NHA groups with the polymer backbone via γ-position could be a rational design for highly alkaline stable AEMs and AEIs. Furthermore, a constant voltage is applied to the QAs electrolyte solution to measure the electrochemical stability by simulating the real operating environment of and AEM water electrolyzers. Compared to structural changes before and after voltage application, NHA exhibits worse stability than alkyl QAs, involving the radical degradation and electrochemical degradation. These results above give us a clearer picture while designing the polymer used for electrochemical devices, which is that a careful balance needs to be established between alkaline and electrochemical durability, especially under the high potential and harsh alkaline environment. References [1] D. Li et al., “Durability of Anion Exchange Membrane Water Electrolyzers,” Energy Environ. Sci., vol. 14, no. 6, pp. 3393-3419, Jan. 2021. [2] M. G. Marino et al., “Alkaline Stability of Quaternary Ammonium Cations for Alkaline Fuel Cell Membranes and Ionic Liquids,” ChemSusChem, vol. 8, no. 3, pp. 513-523, Feb. 2015. [3] D. Li et al., “Phenyl Oxidation Impacts the Durability of Alkaline Membrane Water Electrolyzer,” ACS Appl. Mater. Interfaces, vol. 11, no. 10, pp. 9696-9701, Feb. 2019. Figure 1

The kinetic mechanism of the methanol oxidation reaction (MOR) has been controversial due to the lack of accurate monitoring technology and static calculation of the kinetic process, as well as the failure to consider the relationship between the free energy barriers and electrode potential. This work focused on Pt and PtRu catalysts and assessed the potential-dependent MOR kinetic process via metal–electrolyte models to reconcile the experimental and computational MOR activity. The obtained results demonstrate that the potential-dependent rate-determining steps (RDSs) change with the increase of electrode potential in the orders of (R3: CH₃O* → CH₂O* + H⁺ + e⁻) → (R5: CHO* → CO* + H⁺ + e⁻) → (R14: CO* + OH* → CO₂* + H⁺ + e⁻), and (R4: CH₂O* → CHO* + H⁺ + e⁻) → (R5: CHO* → CO* + H⁺ + e⁻) → (R14: CO* + OH* → CO₂* + H⁺ + e⁻), respectively, which is attributed to the variation in the adsorption of intermediates and strength of the electrochemical double layer (E_field). Furthermore, the potential-dependent coverage of intermediates and degree of rate control (DRC) in the MOR kinetic process draw support from microkinetic modeling. The experimental cyclic voltammograms and theoretical computation are reconciled with max absolute differences (Δ^max _abs) of 0.020 and 0.023 mA cm⁻² for Pt and PtRu, respectively, giving evidence for the nature of higher MOR activity for PtRu. Importantly, our explicitly dynamic approach elucidates the potential-dependent MOR kinetic process at both the molecular and atomic levels and paves the way for the complex multi-electron reaction kinetic simulation.

The alkaline stability of N‐heterocyclic ammonium (NHA) groups is a critical topic in anion‐exchange membranes (AEMs) and AEM fuel cells (AEMFCs). Here, we report a systematic study on the alkaline stability of 24 representative NHA groups at different hydration numbers (λ) at 80 °C. The results elucidate that γ‐substituted NHAs containing electron‐donating groups display superior alkaline stability, while electron‐withdrawing substituents are detrimental to durable NHAs. Density‐functional‐theory calculations and experimental results suggest that nucleophilic substitution is the dominant degradation pathway in NHAs, while Hofmann elimination is the primary degradation pathway for NHA‐based AEMs. Different degradation pathways determine the alkaline stability of NHAs or NHA‐based AEMs. AEMFC durability (from 1 A cm⁻² to 3 A cm⁻²) suggests that NHA‐based AEMs are mainly subjected to Hofmann elimination under 1 A cm⁻² current density for 1000 h, providing insights into the relationship between current density, λ value, and durability of NHA‐based AEMs.

The alkaline stability of N‐heterocyclic ammonium (NHA) groups is a critical topic in anion‐exchange membranes (AEMs) and AEM fuel cells (AEMFCs). Here, we report a systematic study on the alkaline stability of 24 representative NHA groups at different hydration numbers (λ) at 80 °C. The results elucidate that γ‐substituted NHAs containing electron‐donating groups display superior alkaline stability, while electron‐withdrawing substituents are detrimental to durable NHAs. Density‐functional‐theory calculations and experimental results suggest that nucleophilic substitution is the dominant degradation pathway in NHAs, while Hofmann elimination is the primary degradation pathway for NHA‐based AEMs. Different degradation pathways determine the alkaline stability of NHAs or NHA‐based AEMs. AEMFC durability (from 1 A cm⁻² to 3 A cm⁻²) suggests that NHA‐based AEMs are mainly subjected to Hofmann elimination under 1 A cm⁻² current density for 1000 h, providing insights into the relationship between current density, λ value, and durability of NHA‐based AEMs.

Home energy management system (HEMS) is an important part of smart grid terminal. Reasonable scheduling strategy of household load power consumption and energy storage operation can not only relieve the pressure of power grid, but also reduce the electricity costs of users. Therefore, this paper proposed a household energy management strategy based on time-of-use(TOU) electricity tariffs. Firstly, according to the characteristics of household load, it can be divided into three categories: basic load, transferable load(TL) and interruptible load(IL). Then, with the constraints of the dispatchable load and the working state of the energy storage battery, a load optimization scheduling strategy and an energy storage charging and discharging strategy have been formulated with the goal of minimizing the cost of household electricity purchase. Finally, the simulation results show that the proposed optimal scheduling strategy can effectively reduce the peak load and household electricity cost.

In recent years, distribution network is developing rapidly from current to future advanced form. Under the tendency, this article puts forward a new AC and DC distribution network technology based on flexible substation. There is no mature design experience and complete theory for designing, equipment manufacturing and engineering construction, etc. in this technology. In this paper, system design method of AC and DC distribution network based on flexible substation are given systematically. And design of overall system, key equipment parameters, control and protection are researched and discussed. All of the research results above are adopted in the first AC and DC distribution network demonstration project based on flexible substation. The paper will provide theoretical and experimental experience for system design in the future AC and DC distribution network projects.

Today, an important problem in molecular biology is the study of gene expression mechanism. The first step in determining differential gene expression is the binding of sequence specific transcription factors to regulatory regions of the genes. An important aspect to understand how a given transcription factor functions is to know the entire gamut of binding sites and potential target genes that the factor may regulate. In this paper, we presented an improved prediction method based on hidden Markov model (HMM) called BSS-HMM(3)s (binding site search based on third-order HMMs) for transcription factor binding sites. The results show that the predicted sensitivity and specificity of BSS-HMM(3)s increased 11.95 and 12.97%, respectively, compared with Match.