Polyoxometalate-Based Single-Atom Catalyst with Precise Structure and Extremely Exposed Active Site for Efficient H2 Evolution.

Single-atom catalysts with precise structure and extremely high catalytic efficiency remain a fervent focus in the fields of materials chemistry and catalytic science. Herein, a nickel-substituted polyoxometalate (POM) {NiSb6O4(H2O)3[ß-Ni(hmta)SbW8O31]3}15- (NiPOM) with one extremely exposed nickel site [NiO3(H2O)3] was synthesized using the conventional aqueous method. The uniform dispersion of single nickel center with well-defined structure was facilely achieved by anchoring nanosized NiPOM on graphene oxide (GO). The resulting NiPOM/GO can couple with CdS photoabsorber for the construction of low-cost and ultra-efficient hydrogen evolution system. The H2 yield can reach to 2753.27 mmol gPOM-1 h-1, which represents a record value among all the POM-based photocatalytic systems. Remarkablely, an extremely high hydrogen yield of 3647.28 mmol gPOM-1 h-1 was achieved with simultaneous photooxidation of commercial waste plastic, representing the first POM-based photocatalytic system for H2 evolution and waste plastic conversion. This work highlights a straightforward strategy for constructing extremely exposed single-metal site with precise microenvironment by facilely manipulating nanosized molecular cluster to control individual atom.

Theoretical Insights of Curvature Effects of FeN4-Doped Carbon Nanotubes on ORR Activity.

The advancement of metal-air batteries is critically contingent on the progression of efficient catalysts for the oxygen reduction reaction (ORR). The potential applications of a series of FeN4-doped carbon nanotubes (Fe-N4CNTs) of varying diameters as ORR catalysts were examined using density functional theory. We explored the stability and electronic properties of Fe-N4CNTs by analyzing the energy and examining the density of states. A marked dependence of the catalytic performance on the nanotube diameter was observed: as the transition from (5, 5) to (10, 10) Fe-N4CNTs occurred, the catalytic activity on the outer surface of the carbon tubes enhanced progressively, with the overpotential reducing from 0.94 to 0.86 V. Conversely, the catalytic activity on the inner surface of the carbon tubes decreased progressively with the overpotential also increasing from 0.62 to 1.04 V. In addition, we found that curvature significantly affected the electronic structure and charge transfer at the FeN4 site, regulating the adsorption and desorption of reactants, intermediates, and products during electrocatalysis and thus influencing the catalytic activity of the Fe-N4CNTs. This investigation offers valuable guidance for the design of Fe-based single-atom catalysts and the practical application of Fe-N-C materials.