In‐Operando Neutron Diffraction Studies of Transition Metal Hydrogen Storage Materials

Abstract

Hydrogen storage is one of the most important technological issues to be resolved in the move towards a future sustainable hydrogen-based economy. [1][2][3] The multiple technological requirements of safety, durability, recyclability, energy efficiency, high hydrogen capacity and low cost place very significant constraints on the development of a commercially viable hydrogen storage material for transportation. [4][5][6] Over the past decade, many new material systems have been studied as potential hydrogen storage materials. These include complex chemical hydrides such as alanates, amides and borohydrides, molecular hydrides such as ammonia borane and its derivatives and physisorbed systems such as carbon aerogels and metal organic framework materials. [ 7 ] Despite signifi cant advances, no materials have been discovered that have substantially improved overall performance over the current generation of transition metal hydrides. As a possible hydrogen storage system for fuel cell electric vehicles (FCEV), the new highpressure metal hydride (MH) tank system has been reported. [ 8 ] Ti-V-Cr-Mo alloys of body-centred cubic (bcc) structure, which has high reversible hydrogen capacity (2.4 mass% H 2 ) and high dissociation pressure (2.3 MPa at 298 K), have been developed for this MH tank system. [ 9 ] So far, hydrogen storage properties of bcc alloys have been widely studied and it is known that these alloys have the highest reversible hydrogen capacity [10][11][12][13][14][15][16] among current transition metal hydrides, but the hydrogen storage capacity decreases during the absorption and desorption cycle. [17][18][19] In this communication, we report neutron diffraction studies of hydrogen absorption and desorption in a prototypic metal hydride under realistic operating conditions. These in operando neutron diffraction measurements mimic the hydrogen cycling behaviour in the current generation of FCEV. We clarify the detailed behaviour of hydrogen within the alloy crystal structure on absorption and desorption and identify the principal reasons for the degradation of hydrogen storage performance. Our results explain the nature of hydrogen absorption and desorption in the prototypic Ti-V-Cr-Mo transition metal hydride system and also the capacity limitations that develop on prolonged cycling of these materials. We conclude that even with this generation of transition metal hydride the degree of hydrogen sequestration on cycling may be eliminated, which in turn will lead to a higher usable gravimetric capacity. Further optimised alloy systems may reach storage capacities that will approach near-term transportation requirements for FCEV.High initial capacity and good cycling performance are two of the most signifi cant materials properties that must be understood and developed in the search for new hydrogen storage materials. The direct location and nature of hydrogen during cycling is key to this understanding and also to subsequent materials optimisation. [20][21][22][23] However, the determination of hydrogen po...

Understanding composition–property relationships in Ti–Cr–V–Mo alloys for optimisation of hydrogen storage in pressurised tanks

“…This is more pronounced for the 4c site than the 2b. Kamazawa et al 28 highlight that the nearest neighbour tetrahedral and octahedral sites cannot co-exist in the bct phase, owing to spatial constraints, and therefore can be grouped together to form disc sites after determining the site occupancies from Rietveld refinement. The disc sites occur around the 2b octahedral site, also known as the O z site, which has been found to be the primary location of the hydrogen atoms in the bct b-phase of V 2 H, and is the cause of the anisotropic cell expansion from the bcc a-phase.…”

“…V 20 has a higher maximum capacity and a higher dissociation pressure, it also shows significant degradation in the hydrogen capacity on cycling. 28 V 75 has a slightly lower maximum capacity, a significantly lower dissociation pressure, but does not show significant degradation in capacity on cycling (Fig. 1).…”

Time-Resolved In Situ Neutron Diffraction Study of Cu22Fe8Ge4S32 Germanite: A Guide for the Synthesis of Complex Chalcogenides

“…Thanks to the development of dedicated instruments on high flux neutron sources enabling fast data acquisition, 23 in situ neutron powder diffraction has already been used to study the crystallization of amorphous materials, 24,25 cationic ordering, [26][27][28][29] mechanical properties, 30,31 solid-gas reactions, [32][33][34][35] and chemical processes in batteries. [36][37][38][39] To this day, in situ powder neutron diffraction studies dedicated to sulfide materials have been performed only on pre-reacted or already formed sulfides, [40][41][42][43][44][45][46][47][48] mainly to determine their temperature stability and decomposition mechanisms.…”

A Comparative Assessment of Hydrogen Embrittlement: Palladium and Palladium-Silver (25 Weight% Silver) Subjected to Hydrogen Absorption/Desorption Cycling

“…The influence of hydrogen absorption and desorption on many important properties of such systems has been the focus of many fundamental studies into solid-gas systems for decades. There have been investigations focused on the thermodynamic properties of these materials [1], electrical properties [2], optical properties [3], structural properties [4], phase stability properties [5] and mechanical properties [6]. These materials are at the center of truly multidisciplinary investigations and are studied by chemists, physicists, engineers, materials scientists and metallurgists.…”