Hydrogen Storage in Untreated/Ammonia-Treated and Transition Metal-Decorated (Pt, Pd, Ni, Rh, Ir and Ru) Activated Carbons

Abstract

Hydrogen storage may be the bottle neck in hydrogen economy, where hydrogen spillover is in dispute as an effective mechanism. In this context, activated carbon (AC) was doped with nitrogen by using ammonia gas, and was further decorated with platinum, palladium, nickel, rhodium, iridium and ruthenium, via an ultrasound-assisted impregnation method, with average particle sizes of around 74, 60, 78, 61, 67 and 38 nm, respectively. The hydrogen storage was compared, before and after modification at both ambient and cryogenic temperatures, for exploring the spillover effect, induced by the decorating transition metals. Ammonia treatment improved hydrogen storage at both 298 K and 77 K, for the samples, where this enhancement was more remarkable at 298 K. Nevertheless, metal decoration reduced the hydrogen uptake of AC for all of the decorated samples other than palladium at cryogenic temperature, but improved it remarkably, especially for iridium and palladium, at room temperature. This observation suggested that metal decoration’s counter effect overcomes hydrogen spillover at cryogenic temperatures, while the opposite takes place at ambient temperature.

Impact of ammonia treatment and platinum group or nickel metal decoration on the activated carbon storage of carbon dioxide and methane

“…The preparation and characterization of all adsorbents were published in our previous article papers [32,33] and were investigated for hydrogen adsorption and desorption measurements at both room and cryogenic temperatures [32]. In brief, the commercially available Norit AC was doped by 2.0 wt% nitrogen via heat treatment under ammonia flow at 850°C.…”

“…The CO 2 and CH 4 storage uptakes were assessed by measuring the pressure-composition-isotherms (PCI) at RT and up to 5.0 bar for CO 2 and 100 bar for CH 4 . The PCI curves were measured 5 times for validity and repeatability of the results, where the details of characterizations were elucidated in [32,33].…”

“…Furthermore, the high tetrahedral symmetry of the CH 4 gas molecules may prevent the formation of polar interactions on the surface of the transition metals [115] . At 5.0 bar, the storage capacity of CO 2 was as∼6 folds as that of CH 4 and as 530 folds as that of hydrogen at ambient temperature [32], a feature enables the upgrading of natural gas as clean fuel sources after the removal of CO 2 contamination by physical adsorption. While purifying hydrogen from CO 2 impurities is essential, it would be so beneficial for numerous industries such as steam reforming of methane (SRM) [116,117], water gas shift (WGS) [118,119], and ammonia synthesis [120,121].…”

“…Chemical adsorption as methane hydrates is another storage option, but the problems associated with the sluggish adsorption kinetics and the difficulties in releasing methane back in the desorption process make this technique inadequate [31]. Physical adsorption process allows the spontaneously physical attraction of gas molecules to the surface of the porous materials due to van der Waals attraction forces [32,33]. These forces are nonspecific interactions, but when polar molecules are involved in the adsorption with polar or ionic surfaces, these interactions are specific and would remain as physisorption state as long as no chemical bonding or electronic perturbation of the adsorbed molecules [34,35].…”

Potential hydrogen storage materials from Li decorated N‐doped Me‐graphene

“…27,28 However, transition metals have high cohesive energy which is easy to form metal clusters on the carbon basis, thus reducing the adsorption capacity of hydrogen molecules. 29,30 In addition, the transition metal adsorption of hydrogen may be achieved by dissociation with higher binding energy, which is more prone to reverse desorption at high temperatures. [31][32][33] For alkali metals and alkaline earth metals, they both have lower binding energy, but the former has lighter weight.…”