Electrochemical reduction of CO2 (CO2RR) provides an attractive pathway to achieve a carbon-neutral energy cycle. Single-atom catalysts (SAC) have shown unique potential in heterogeneous catalysis, but their structural simplicity prevents them from breaking linear scaling relationships. In this study, we develop a feasible strategy to precisely construct a series of electrocatalysts featuring well-defined single-atom and dual-site iron anchored on nitrogen-doped carbon matrix (Fe1–N–C and Fe2–N–C). The Fe2–N–C dual-atom electrocatalyst (DAC) achieves enhanced CO Faradaic efficiency above 80% in wider applied potential ranges along with higher turnover frequency (26,637 h–1) and better durability compared to SAC counterparts. Furthermore, based on in-depth experimental and theoretical analysis, the orbital coupling between the iron dual sites decreases the energy gap between antibonding and bonding states in *CO adsorption. This research presents new insights into the structure–performance relationship on CO2RR electrocatalysts at the atomic scale and extends the application of DACs for heterogeneous electrocatalysis and beyond.

Single‐atom nanozymes (SAzymes) are promising in next‐generation nanozymes, nevertheless, how to rationally modulate the microenvironment of SAzymes with controllable multi‐enzyme properties is still challenging. Herein, we systematically investigate the relationship between atomic configuration and multi‐enzymatic performances. The constructed MnSA−N3‐coordinated SAzymes (MnSA−N3−C) exhibits much more remarkable oxidase‐, peroxidase‐, and glutathione oxidase‐like activities than that of MnSA−N4−C. Based on experimental and theoretical results, these multi‐enzyme‐like behaviors are highly dependent on the coordination number of single atomic Mn sites by local charge polarization. As a consequence, a series of colorimetric biosensing platforms based on MnSA−N3−C SAzymes is successfully built for specific recognition of biological molecules. These findings provide atomic‐level insight into the microenvironment of nanozymes, promoting rational design of other demanding biocatalysts.

to CO suffer from sluggish reaction kinetics and ambiguous mechanism. [5] Therefore, efficient and selective electrocatalysts for the reduction of CO 2 to CO should be found.Metal-nitrogen−doped carbon (M-N-C) catalysts are promising candidates as catalysts for electrochemical conversion of CO 2 to CO. [6] M-N-C catalysts that include M-N 4 centers are similar to molecular metalloenzyme systems, which have tremendous potential for CO production. [7] Recently, numerous studies have constructed noble metal (Au, Ag, Pt, Pd, and Ir), [8] transition metal (Fe, Co, Ni, Cu, Zn, Mn, Cd, and Cr), [9] and p-block metal (Bi, Sn, and Sb) [10] based M-N-C electrocatalysis for CO 2 RR to produce CO. [11] Theoretical calculations and experimental verifications have identified that the metal centers in the M-N 4 -C matrix are primary catalytic active sites for CO 2 adsorption and reduction. [12] Nevertheless, previous studies evaluated the CO 2 -to-CO efficiency of M-N-C catalysts merely by changing metals, without a systematic screening process. [13] For example, Ju et al. has compared the CO 2 RR activity of M-N-C (M = Fe, Co, Ni, Mn, and Cu) catalysts and analyzed reactivity trends according to various overpotential ranges. [14] More recently, Wang et al. has reported M-N-C catalysts (M = Fe, Co, and Ni) with a metal-pyridine N structure and demonstrated their selectivity order for CO 2 -to-CO conversion. [15] Moreover, most typically theoretical studies have proposed a single descriptor such as the difference between limiting potentials for CO 2 RR and the hydrogen evolution reaction (HER), which was denoted as U L (CO 2 )-U L (H 2 ), to quantify the selectivity of CO 2 RR limitedly. [16] However, the selectivity of CO generation in experiments varies with electrochemical potential so U L (CO 2 )-U L (H 2 ) as a descriptor does not completely describe the efficiency of the reaction. As a result, a general descriptor should be sought, and a systematic screening approach should be developed to find superior M-N 4 -C for CO 2 RR to CO production.Here, we used theoretical studies to develop a universal procedure for screening suitable M-N 4 -C electrocatalysts, which could transform CO 2 to CO with high activity and selectivity. Twenty-three M-N 4 -C candidates were chosen and input into this screening system. The selectivity, activity, and structural stability for CO 2 RR-to-CO were evaluated in a systematic sequence To identify high-efficiency metal-nitrogen-doped (M-N-C) electrocatalysts for the electrochemical CO 2 -to-CO reduction reaction (CO 2 RR), a method that uses density functional theory calculation is presented to evaluate their selectivity, activity, and structural stability. Twenty-three M-N 4 -C catalysts are evaluated, and three of them (M = Fe, Co, or Ni) are identified as promising candidates. They are synthesized and tested as proof-of-concept catalysts for CO 2 -to-CO conversion. Different key descriptors, including the maximum reaction energy, differences of the *H and *CO binding energy (ΔG *H −ΔG *CO ...

ZnO has been studied intensely for chemical sensors due to its high sensitivity and fast response. Here, we present a simple approach to precisely control oxygen vacancy contents to provide significantly enhanced acetone sensing performance of commercial ZnO nanopowders. A combination of H2O2 treatment and thermal annealing produces optimal surface defects with oxygen vacancies on the ZnO nanoparticles (NPs). The highest response of ∼27,562 was achieved for 10 ppm acetone in 0.125 M H2O2 treated/annealed ZnO NPs at the optimal working temperature of 400 °C, which is significantly higher than that of reported so far in various acetone sensors based on metal oxide semiconductors (MOSs). Furthermore, first-principles calculations indicate that pre-adsorbed O formed on the surface of H2O2 treated ZnO NPs can provide favorable adsorption energy, especially for acetone detection, due to strong bidentate bonding between carbonyl C atom of acetone molecules and pre-adsorbed O on the ZnO surface. Our study demonstrates that controlling surface oxygen vacancies by H2O2 treatment and re-annealing at optimal temperature is an effective method to improve the sensing properties of commercial MOS materials.

A surficial molecular dipole effect depending on ion‐molecular interactions has been crucial issues regarding to an interfacial potential, which can modulate solid electronic and electrochemical systems. Their properties near the interfacial region can be dictated by specific interactions between surface and adsorbates, but understandings of the corresponding details remain at interesting issues. Here, intuitive observations of an ionic pair formation‐induced interfacial potential shifts are presented with an ionovoltaic system, and corresponding output signal variations are analyzed in terms of the surficial dipole changes on self‐assembled monolayer. With aiding of photoelectron spectroscopies and density function theory simulation, the ionic pair formation‐induced potential shifts are revealed to strongly rely on a paired molecular structure and a binding affinity of the paired ionic moieties. Chemical contributions to the binding event are interrogated in terms of polarizability in each ionic group and consistent with chaotropic/kosmotropic character of the ionic groups. Based on these findings, the ionovoltaic output changes are theoretically correlated with an adsorption isotherm reflecting the molecular dipole effect, thereby demonstrating as an efficient interfacial molecular probing method under electrolyte interfacing conditions.