Self-enhanced localized alkalinity at the encapsulated Cu catalyst for superb electrocatalytic nitrate/nitrite reduction to NH3 in neutral electrolyte.

The electrocatalytic nitrate/nitrite reduction reaction (eNOx-RR) to ammonia (NH3) is thermodynamically more favorable than the eye-catching nitrogen (N2) electroreduction. To date, the high eNOx-RR-to-NH3 activity is limited to strong alkaline electrolytes but cannot be achieved in economic and sustainable neutral/near-neutral electrolytes. Here, we construct a copper (Cu) catalyst encapsulated inside the hydrophilic hierarchical nitrogen-doped carbon nanocages (Cu@hNCNC). During eNOx-RR, the hNCNC shell hinders the diffusion of generated OH- ions outward, thus creating a self-enhanced local high pH environment around the inside Cu nanoparticles. Consequently, the Cu@hNCNC catalyst exhibits an excellent eNOx-RR-to-NH3 activity in the neutral electrolyte, equivalent to the Cu catalyst immobilized on the outer surface of hNCNC (Cu/hNCNC) in strong alkaline electrolyte, with much better stability for the former. The optimal NH3 yield rate reaches 4.0 moles per hour per gram with a high Faradaic efficiency of 99.7%. The strong-alkalinity-free advantage facilitates the practicability of Cu@hNCNC catalyst as demonstrated in a coupled plasma-driven N2 oxidization with eNOx-RR-to-NH3.

Correlation between Heteroatom Coordination and Hydrogen Evolution for Single-site Pt on Carbon-based Nanocages.

The electrocatalytic performance of single-site catalysts (SSCs) is closely correlated with the electronic structure of metal atoms. Herein we construct a series of Pt SSCs on heteroatom-doped hierarchical carbon nanocages, which exhibit increasing hydrogen evolution reaction (HER) activities along S-doped, P-doped, undoped and N-doped supports. Theoretical simulation indicates a multi-H-atom adsorption process on Pt SSCs due to the low coordination, and a reasonable descriptor is figured out to evaluate the HER activities. Relative to C-coordinated Pt, N-coordinated Pt has higher reactivity due to the electron transfer of N-to-Pt, which enriches the density of states of Pt 5d orbital near the Fermi level and facilitates the capturing of protons, just the opposite to the situations for P- and S-coordinated ones. The stable N-coordinated Pt originates from the kinetic stability throughout the multi-H-atom adsorption process. This finding provides a significant guidance for rational design of advanced Pt SSCs on carbon-based supports.

Constructing Gold Single-Atom Catalysts on Hierarchical Nitrogen-Doped Carbon Nanocages for Carbon Dioxide Electroreduction to Syngas.

Precious-metal single-atom catalysts (SACs), featured by high metal utilization and unique coordination structure for catalysis, demonstrate distinctive performances in the fields of heterogeneous and electrochemical catalysis. Herein, gold SACs are constructed on hierarchical nitrogen-doped carbon nanocages (hNCNC) via a simple impregnation-drying process and first exploited for electrocatalytic carbon dioxide reduction reaction (CO2RR) to produce syngas. The as-constructed Au SAC exhibits the high mass activity of 3319 A g-1 Au at -1.0 V (vs reversible hydrogen electrode, RHE), much superior to the Au nanoparticles supported on hNCNC. The ratio of H2/CO can be conveniently regulated in the range of 0.4-2.2 by changing the applied potential. Theoretical study indicates such a potential-dependent H2/CO ratio is attributed to the different responses of HER and CO2RR on Au single-atom sites coordinating with one N atom at the edges of micropores across the nanocage shells. The catalytic mechanism of the Au active sites is associated with the smooth switch between twofold and fourfold coordination during CO2RR, which much decreases the free energy changes of the rate-determining steps and promotes the reaction activity.

Encapsulation of Red Phosphorus in Carbon Nanocages with Ultrahigh Content for High-Capacity and Long Cycle Life Sodium-Ion Batteries.

Red phosphorus (RP) has attracted great attention as a potential candidate for anode materials of high-energy density sodium-ion batteries (NIBs) due to its high theoretical capacity, appropriate working voltage, and natural abundance. However, the low electrical conductance and huge volumetric variation during the sodiation-desodiation process, causing poor rate performance and cyclability, have limited the practical application of RP in NIBs. Herein, we report a rational strategy to resolve these issues by encapsulating nanoscaled RP into conductive and networked carbon nanocages (denoted as RP@CNCs) using a combination of a phosphorus-amine based method and evacuation-filling process. The large interior cavities volume of CNCs and controllable solution-based method enable the ultrahigh RP loading amount (85.3 wt %) in the RP@CNC composite. Benefiting from the synergic effects of the interior cavities and conductive network, which afford high structure stability and rapid electron transport, the RP@CNC composite presents a high systematic capacity of 1363 mA h g-1 at a current density of 100 mA g-1 after 150 cycles, favorable high-rate capability, and splendid long-cycling performance with capacity retention over 80% after 1300 cycles at 5000 mA g-1. This prototypical design promises an efficient solution to maximize RP loading as well as to boost the electrochemical performance of RP-based anodes.

Electrocatalysis of S-doped carbon with weak polysulfide adsorption enhances lithium-sulfur battery performance.

Heteroatom-doped nanocarbons are beneficial for the performance improvement of lithium-sulfur batteries, and the reason is usually attributed to their strong adsorption to the soluble polysulfides. Herein, we found that, despite the weak polysulfide adsorption on hierarchical S-doped carbon nanocages (hSCNCs), the hSCNC-encapsulated sulfur cathode still exhibited better performance than the counterpart using undoped carbon nanocages, showing a high capacity of 579 mA h g-1 at 2 A g-1 after 400 cycles, and a high areal capacity of 4.7 mA h cm-2 with a high sulfur loading of 4.5 mg cm-2. The electrocatalysis-promoted mechanism of S-doped carbon was demonstrated, which facilitated polysulfide conversion and suppressed the polarization effect, thereby leading to superior performance.