Modulation of Mo-Fe-C sites over mesoscale diffusion-enhanced hollow sub-micro reactors toward boosted electrochemical water oxidation

Simultaneously engineering the mesoscale mass transfer and surface reactions on the electrode can promote the kinetics of oxygen evolution reaction (OER). Herein, we report the simultaneously modulation of the mesoscale diffusion and Mo-Fe-C sites formation over monodispersed hollow Fe@MoS2-C sub-micro reactors for boosted OER performance. According to finite element simulation and analysis, the hollow nanostructured MoS2-C host possessed much better mesoscale diffusion properties than its solid and yolk–shell counterparts. Notably, the sulfur vacancies and intercalated carbon in the sub-micro reactor offered a unique microenvironment for Fe anchoring on Mo-Fe-C sites. The stability and activity of the sites were revealed by theoretical calculations. The resultant Fe@MoS2-C presented an OER overpotential of 194 mV, which is much better than those of the Fe-based single-atom catalysts reported to data. Our monodispersed sub-micro reactor combined the advantage of mesoscale diffusion and single-atom sites, and it may have broad prospects for complex electrocatalytic reactions.

Sorption and diffusion properties of untreated and thermally modified beech wood dust

Dynamic water vapor sorption experiments were carried out using beech wood dust (from untreated and thermally modified wood) of two-particle sizes, (< 25 and 80–250 µm), obtained from abrasive sanding. Sorption isotherms were parameterized with the GAB and GDW models. Dust from thermally modified wood had significantly lower equilibrium moisture content compared to dust from untreated material, due to the reduction in primary sorption sites in treated material. The observed changes were quantified by the coefficients of the GAB and GDW models. Thermal modification and size of wood dust particles had no influence on binding energy of water molecules being linked to the secondary sorption sites. Water diffusivity decreased significantly with increasing moisture content, but only for monolayer sorption. For higher moisture content values, water diffusivity was practically independent of moisture content. These results were found for untreated and thermally modified material as well as for both dust size fractions. The influence of thermal modification on water diffusivity was unclear, which is attributed to the diffusion model, which represents dust particles as spheres and assumes instant hygroscopic equilibrium. Overall, this study indicates that the effectiveness of filtration processes likely depends strongly on sorption and diffusion properties of wood dust only at low moisture contents within the hygroscopic range.

Modelling and asymptotic analysis of the concentration difference in a nanoregion between an influx andoutflux diffusion acrossnarrow windows

When a flux of Brownian particles is injected in a narrow window located on the surface of a bounded domain, these particles diffuse and can eventually escape through a cluster of narrow windows. At steady state, we compute asymptotically the distribution of concentration between the different windows. The solution is obtained by solving Laplace’s equation using Green’s function techniques and second-order asymptotic analysis, and depends on the influx amplitude, the diffusion properties, as well as the geometrical organization of all the windows, such as their distances and the mean curvature. We explore the range of validity of the present asymptotic expansions using numerical simulations of the mixed boundary value problem. Finally, we introduce a length scale to estimate how deep inside a domain a local diffusion current can spread.