Lachawiec Anthony J, DiRaimondo Thomas R, Yang Ralph T
Department of Chemical Engineering, University of Michigan, 3074 HH Dow Building, Ann Arbor, MI 48109, USA.
Rev Sci Instrum. 2008 Jun;79(6):063906. doi: 10.1063/1.2937820.
A volumetric apparatus to measure hydrogen adsorption and desorption at room temperature and up to 100 atm has been constructed and studied for accuracy, reproducibility, and stability. The design principles are presented and considerable attention to detail is given to examine the effects of diurnal temperature changes in the manifold and helium adsorption by carbon-based adsorbents during free volume measurement. A heuristic for helium correction is derived from a model with a basis in literature and verified through calculation of adsorbent density. Several materials with well-known hydrogen capacities are studied to examine reproducibility. The microporous carbon AX-21 is studied to examine the effects of pressure step size and approach to equilibrium caused by gas mixing and the Joule-Thomson effect. Hydrogen spillover on a hybrid material, Pt on templated carbon, is examined for several loadings of metal. Kinetics of both physisorption and spillover are compared via the diffusion time constant (D/R(2)) estimated by fitting models for pore and surface diffusion to time-dependent adsorption profiles. No concentration dependence was found for pore diffusion; however, the surface diffusion time constant was shown to decrease with respect to increasing hydrogen concentration.
已构建了一种用于在室温及高达100个大气压下测量氢吸附和解吸的体积测量装置，并对其准确性、可重复性和稳定性进行了研究。介绍了设计原理，并特别关注细节，以研究歧管中昼夜温度变化以及在自由体积测量期间碳基吸附剂对氦的吸附的影响。从基于文献的模型中推导出氦校正的启发式方法，并通过吸附剂密度的计算进行验证。研究了几种具有已知氢容量的材料以检验可重复性。研究了微孔碳AX-21，以检验压力步长以及气体混合和焦耳-汤姆逊效应引起的接近平衡的影响。研究了负载几种金属的混合材料（模板碳上的Pt）上的氢溢出。通过将孔隙和表面扩散模型拟合到随时间变化的吸附曲线来估计扩散时间常数（D/R(2)），比较了物理吸附和溢出的动力学。未发现孔隙扩散与浓度有关；然而，表面扩散时间常数显示随着氢浓度的增加而减小。
