Revealing the Adsorption Behavior of Nitrogen Reduction Reaction on Strained Ti2 CO2 by a Spin-Polarized d-band Center Model.

Electrocatalytic reduction of dinitrogen to ammonia has attracted significant research interest. Herein, it reports the boosting performance of electrocatalytic nitrogen reduction on Ti2 CO2 MXene with an oxygen vacancy through biaxial tensile strain engineering. Specifically, tensile strain modified electronic structures and formation energy of oxygen vacancy are evaluated. The exposed Ti atoms with additional electron states near the Fermi level serve as active site for intermediate adsorption, leading to superior catalytic performance (Ulimit = -0.44 V) under 2.5% biaxial tensile strain through a distal mechanism. However, the two sides of the "Sabatier optimum" in volcano plot are not limited by two different electronic steps, but are induced by the diverse adsorption behaviors of intermediates. Crucially, the "Sabatier optimum" results from the different response speeds of the adsorption energy for *N2 and *NNH to strains. Moreover, the authors observe conventional d-band adsorption for *N2 and *NNH, non-linear adsorption for *NNH2 , and abnormal d-band adsorption for *N, *NH, *NH2 , and *NH3 , which can be explained by the competition between attractive orbital hybridization and repulsive orbital orthogonalization with the spin-polarized d-band model, which further clarifies the contributions of 3σ → dz2 and dxz /dyz → 2π* to the overall population of bonding and anti-bonding states.

S-functionalized 2D V2B as a promising anode material for rechargeable lithium ion batteries.

The development of novel high specific capacity anode materials is urgently needed for rechargeable metal ion batteries. Herein, S-functionalized V2B as the electrode material for Li/Na/K ion batteries are comprehensively investigated using first-principles calculations. Specifically, V2BS2 was verified with good electrical conductivity via band structure and density of states calculations. Phonon dispersion and ab initio molecular dynamic simulations were performed and confirmed the dynamic and thermal stability of V2BS2. The use of V2BS2 with a high theoretical specific capacity of 606 mA h g-1 for lithium ion batteries (LIBs) due to the bilayer adsorption of Li atoms is encouraging, which is attributed to the double empty orbitals of the S atoms and small lattice mismatch (1.5%) between the Li layers and substrate. Furthermore, dendrite formation would be well prohibited and safety issues for battery operation would be ensured for V2BS2 as electrode materials because of the low open circuit voltage with 0.37 V. The high charge/discharge rate for LIBs is also achievable owing to the high mobility of adatoms on the surface of V2BS2. Our work not only finds use as a promising material for the field of energy storage, but also provides constructive design strategies for developing high performance anode materials for rechargeable metal ion batteries.

Manipulating Electric Double Layer Adsorption for Stable Solid-Electrolyte Interphase in 2.3†Ah Zn-Pouch Cells.

Constructing a reliable solid-electrolyte interphase (SEI) is imperative for enabling highly reversible zinc metal (Zn0 ) electrodes. Contrary to conventional "bulk solvation" mechanism, we found the SEI structure is dominated by electric double layer (EDL) adsorption. We manipulate the EDL adsorption and Zn2+ solvation with ether additives (i.e. 15-crown-5, 12-crown-4, and triglyme). The 12-crown-4 with medium adsorption on EDL leads to a layer-structured SEI with inner inorganic ZnFx /ZnSx and outer organic C-O-C components. This structure endows SEI with high rigidness and strong toughness enabling the 100 cm2 Zn||Zn pouch cell to exhibit a cumulative capacity of 4250 mAh cm-2 at areal-capacity of 10 mAh cm-2 . More importantly, a 2.3 Ah Zn||Zn0.25 V2 O5 ⋅n H2 O pouch cell delivers a recorded energy density of 104 Wh Lcell -1 and runs for >70 days under the harsh conditions of low negative/positive electrode ratio (2.2 : 1), lean electrolyte (8 g Ah-1 ), and high-areal-capacity (≈13 mAh cm-2 ).

Establishing an orbital-level understanding of active origins of heteroatom-coordinated single-atom catalysts: The case of N2 reduction.

Heteroatom-coordinated single-atom catalysts (SACs) supported by porous graphene exhibit high activity in electrochemical reduction reactions. However, the underlying active origins are complex and puzzling, hindering the development of efficient catalysts. Herein, we investigate the active origins of heteroatom-coordinated Fe-XmYn SACs (X, Y = B, C, N, O, m + n = 4) toward nitrogen reduction reaction (NRR) as a model reaction, through comprehensive analysis of structural, energetic, and electronic parameters. Specifically, the number and arrangement of heteroatoms are found to significantly affect the degree of d-orbital splitting and magnetic moment of the Fe center. Moreover, d-orbital splitting energy (dSE), rather than the conventional d-band theory, explains the adsorption behavior of intermediates in multi-step electron-proton coupling (EPC) reactions. In addition, both s- and d-orbitals of Fe are found to be important for Fe-N bonding, which promotes charge transfer (CT) and N2 activation. Importantly, CT is thought to influence the Pauli repulsion and orbital interaction. Correspondingly, relationships are unveiled between limiting potential (Ulimit) and adsorption energy ΔE(*NNH), dSE, CT, Fe-N bond. In all, this work provides orbital-level insights into the active origins of Fe-XmYn SACs, contributing to the understanding of intrinsic mechanism and the design of electrocatalysts for multi-step EPC reactions.

Development of rechargeable high-energy hybrid zinc-iodine aqueous batteries exploiting reversible chlorine-based redox reaction.

The chlorine-based redox reaction (ClRR) could be exploited to produce secondary high-energy aqueous batteries. However, efficient and reversible ClRR is challenging, and it is affected by parasitic reactions such as Cl2 gas evolution and electrolyte decomposition. Here, to circumvent these issues, we use iodine as positive electrode active material in a battery system comprising a Zn metal negative electrode and a concentrated (e.g., 30 molal) ZnCl2 aqueous electrolyte solution. During cell discharge, the iodine at the positive electrode interacts with the chloride ions from the electrolyte to enable interhalogen coordinating chemistry and forming ICl3-. In this way, the redox-active halogen atoms allow a reversible three-electrons transfer reaction which, at the lab-scale cell level, translates into an initial specific discharge capacity of 612.5 mAh gI2-1 at 0.5 A gI2-1 and 25 °C (corresponding to a calculated specific energy of 905 Wh kgI2-1). We also report the assembly and testing of a Zn | |Cl-I pouch cell prototype demonstrating a discharge capacity retention of about 74% after 300 cycles at 200 mA and 25 °C (final discharge capacity of about 92 mAh).