Designing Efficient Nitrate Reduction Electrocatalysts by Identifying and Optimizing Active Sites of Co-Based Spinels.

Cobalt-based spinel oxides (i.e., Co3O4) are emerging as low-cost and selective electrocatalysts for the electrochemical nitrate reduction reaction (NO3-RR) to ammonia (NH3), although their activity is still unsatisfactory and the genuine active site is unclear. Here, we discover that the NO3-RR activity of Co3O4 is highly dependent on the geometric location of the Co site, and the NO3-RR prefers to occur at octahedral Co (CoOh) rather than tetrahedral Co (CoTd) sites. Moreover, CoOhO6 is electrochemically transformed to CoOhO5 along with the formation of O vacancies (Ov) during the process of NO3-RR. Both experimental and theoretic results reveal that in situ generated CoOhO5-Ov configuration is the genuine active site for the NO3-RR. To further enhance the activity of CoOh sites, we replace inert CoTd with different contents of Cu2+ cations, and a volcano-shape correlation between NO3-RR activity and electronic structures of CoOh is observed. Impressively, in 1.0 M KOH, (Cu0.6Co0.4)Co2O4 with optimized CoOh sites achieves a maximum NH3 Faradaic efficiency of 96.5% with an ultrahigh NH3 rate of 1.09 mmol h-1 cm-2 at -0.45 V vs reversible hydrogen electrode, outperforming most of other reported nonprecious metal-based electrocatalysts. Clearly, this work paves new pathways for boosting the NO3-RR activity of Co-based spinels by tuning local electronic structures of CoOh sites.

Unlocking the Transition of Electrochemical Water Oxidation Mechanism Induced by Heteroatom Doping.

Heteroatom doping has emerged as a highly effective strategy to enhance the activity of metal-based electrocatalysts toward the oxygen evolution reaction (OER). It is widely accepted that the doping does not switch the OER mechanism from the adsorbate evolution mechanism (AEM) to the lattice-oxygen-mediated mechanism (LOM), and the enhanced activity is attributed to the optimized binding energies toward oxygen intermediates. However, this seems inconsistent with the fact that the overpotential of doped OER electrocatalysts (<300 mV) is considerably smaller than the limit of AEM (>370 mV). To determine the origin of this inconsistency, we select phosphorus (P)-doped nickel-iron mixed oxides as the model electrocatalysts and observe that the doping enhances the covalency of the metal-oxygen bonds to drive the OER pathway transition from the AEM to the LOM, thereby breaking the adsorption linear relation between *OH and *OOH in the AEM. Consequently, the obtained P-doped oxides display a small overpotential of 237 mV at 10 mA cm-2 . Beyond P, the similar pathway transition is also observed on the sulfur doping. These findings offer new insights into the substantially enhanced OER activity originating from heteroatom doping.

[Reconstruction of maxillary sinus lateral bone wall and mucosa defect of with collagen sponge and acellular cancellous bone combined with bone morphogenetic protein-2].

OBJECTIVE: To investigate the effects of reconstruction of maxillary sinus lateral bone wall and mucosa defect with collagen sponge and acellular cancellous bone combined with bone morphogenetic protein (BMP)-2 in situ. We observed the effect of the reparation and the BMP-2 induced osteogenesis. METHODS: Ten New Zealand white rabbits underwent removal of part of unilateral maxillary sinus lateral bone wall with mucosa, and then divided into 2 equal groups: experimental group and control group. Acellular porcine cancellous vertebral bone was obtained, combined with BMP-2, trimmed to suit the defect, and put into the defect of the experimental group with collagen sponge soaked in venous blood, fixed by protein glue. Same porcine cancellous vertebral bone without BMP-2 was used in the control group. After 3 months the rabbits were killed to observe the osteogenesis of the defects. RESULTS: The rabbits recovered soon after surgery. The implanted acellular cancellous bones were banded tightly with the bones around the defects, the medial surfaces of the materials were covered with mucosa, and new bone tissue entered into the pores of the complex BMP-2 materials. In the control group, only fibrillar connective tissue was filled in the pores. CONCLUSION: BMP-2 can induce osteogenesis, and collagen sponge serves to support the mucosal regeneration. Collagen sponge and acellular cancellous bone combined with BMP-2 can be used to repair the defects of the maxillary sinus bone wall and mucosa.