Size-induced d band center upshift of copper for efficient nitrate reduction to ammonia.

Electrocatalytic nitrate reduction (NO3RR) technique has emerged as a hotspot in NH3 production, for its practicability, and a series of advanced electrocatalysts with high activity and robust stability needed to be constructed in today's era. In this work, size-tunable Cu nanoparticles on porous nitrogen-doped hexagonal carbon nanorods (Cu@NHC) were reasonably designed and served for catalyzing NO3RR in neutral media. Especially, Cu30%@NHC demonstrated a remarkable electroactivity for NH3 production as it showed a suitable grain size with massive catalytic centers and favorable d band structure with faster *NO3--to-*NO2- catalytic dynamics. As expected, Cu30%@NHC (3628.28 µg h-1 mgcat.-1) had a much higher NH3 yield than those for Cu20%@NHC (1268.42 µg h-1 mgcat.-1) and Cu40%@NHC (725.03 µg h-1 mgcat.-1). And those collected NH3 products indeed derived from NO3RR process revealed by 15N isotope-labeling and systemic control tests. Moreover, Cu30%@NHC was also durable for NO3RR bulk electrolysis with minor loss in activity. This work offered an effective modifying tactics to boost NO3RR catalysis and could guide the design of other advanced electrocatalysts via size-induced surface engineering.

Cation Concavities Induced d-Band Electronic Modulation on Co/FeOx Nanostructure to Activate Molecular and Interfacial Oxygen for CO Oxidation.

Cobalt-based catalysts have been identified for effective CO oxidation, but their activity is limited by molecular O2 and interfacial oxygen passivation at low temperatures. Optimization of the d-band structure of the cobalt center is an effective method to enhance the dissociation of oxygen species. Here, we developed a novel Co/FeOx catalyst based on selective cationic deposition to anchor Co cations at the defect site of FeOx, which exhibited superior intrinsic low-temperature activity (100%, 115 °C) compared to that of Pt/Co3O4 (100%, 140 °C) and La/Co2O3 (100%, 150 °C). In contrast to catalysts with oxygen defects, the cationic Fe defect in Co/FeOx showed an exceptional ability to accept electrons from the Co 3d orbital, resulting in significant electron delocalization at the Co sites. The Co/FeOx catalyst exhibited a remarkable turnover frequency of 178.6 per Co site per second, which is 2.3 times higher than that of most previously reported Co-based catalysts. The d-band center is shifted upward by electron redistribution effects, which promotes the breaking of the antibonding orbital *π of the O═O bond. In addition, the controllable regulation of the Fe-Ov-Co oxygen defect sites enlarges the Fe-O bond from 1.97 to 2.02 Å to activate the lattice oxygen. Moreover, compared to CoxFe3-xO4, Co/FeOx has a lower energy barrier for CO oxidation, which significantly accelerates the rate-determining step, *COO formation. This study demonstrates the feasibility of modulating the d-band structure to enhance O2 molecular and interfacial lattice oxygen activation.

Tailoring the d-band electronic structure of deficient LaMn0.3Co0.7O3-δ perovskite nanofibers for boosting oxygen electrocatalysis in Zn-Air batteries.

The development and design of efficient bifunctional electrocatalysts towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial for rechargeable Zinc-air batteries (ZABs). Optimizing the d-band structure of active metal center in perovskite oxides is an effective method to enhance ORR/OER activity by accelerating the rate-determining step. Herein, we report a deficient method to optimize the d-band structure of Co ions in LaMn0.3Co0.7O3-δ (LMCO-2) perovskite nanofibers, which regulates the mutual effect between B-site Co ions and reactive oxygen intermediates. It is proved by experiment and theoretical calculation that the d-band center (Md) of transition metal ions in LMCO-2 is moved up and the electron filling number of eg orbital in B site is 1.01, thus leading to the reduction of Gibbs free energy required for ORR rate-determining step (OH*→H2O*) to 0.22 eV and promoting reaction proceeds. In this manner, LMCO-2 showed good bifunctional oxygen electrocatalytic activity, with a half-wave potential of 0.71 V vs. RHE. Furthermore, the high specific capacity of 811.54 mAh g-1 and power density of 326.56 mW cm-2 were obtained by using LMCO-2 as the cathode catalyst for ZABs. This study proved the feasibility of d-band structure regulation to enhance the electrocatalytic activity of perovskite oxides.

Tailoring the Electronic Structure of Nanoelectrocatalysts Induced by a Surface-Capping Organic Molecule for the Oxygen Reduction Reaction.

Capping organic molecules, including oleylamine, strongly adsorbed onto Pt nanoparticles during preparation steps are considered undesirable species for the oxygen reduction reaction due to decreasing electrochemical active sites. However, we found that a small amount of oleylamine modified platinum nanoparticles showed significant enhancement of the electrochemical activity of the oxygen reduction reaction, even with the loss of the electrochemically active surface area. The enhancement was correlated with the downshift of the frontier d-band structure of platinum and the retardation of competitively adsorbed species. These results suggest that a capping organic molecule modified electrode can be a strategy to design an advanced electrocatalyst by modification of electronic structures.