Enhanced hydrogen storage in sandwich-structured rGO/Co_1−xS/rGO hybrid papers through hydrogen spillover

Reduced graphene oxide (rGO) based two-dimensional (2D) structures have been fabricated for electrochemical hydrogen storage. However, the effective transfer of atomic hydrogen to adjacent rGO surfaces is suppressed by binders, which are widely used in conventional electrochemical hydrogen storage electrodes, leading to a confining of the performance of rGO for hydrogen storage. As a proof of concept experiment, a novel strategy is developed to fabricate the binder-free sandwich-structured rGO/Co_1−xS/rGO hybrid paper via facile ball milling and filtration process. Based on the structure investigation, Co_1−xS is immobilized in the space between the individual rGO sheets by the creation of chemical “bridges” (C[sbnd]S bonds). Through the C[sbnd]S bonds, the atomic hydrogen is transferred from Co_1−xS to rGO accompanying a C[sbnd]H chemical bond formation. When used as an electrode, the hybrid paper exhibits an improved hydrogen storage capacity of 3.82 wt% and, most importantly, significant cycling stability for up to 50 cycles. Excluding the direct hydrogen storage contribution from the Co_1−xS in the hybrid paper, the hydrogen storage ability of rGO is enhanced by 10× through the spillover effects caused by the Co_1−xS modifier.