We produced van der Waals heterostructures of graphene and MoS2 using layer-by-layer stacking. We then tuned the HER efficacy of the van der Waals solids by varying the stacking sequence, and studied four different working electrodes for their HER efficiency, namely graphene (SLGR), MoS2(MS), graphene-MoS2(GRMS) and MoS2-graphene(MSGR). MSGR showed the lowest charge transfer resistance and highest (ever reported) exchange current density.

In the first-order approximation, charge redistribution might occur between the neighbouring (and even more distant) layered crystals in the stack. Neighbouring crystals can also induce structural changes in the adjacent layers. Furthermore, such changes can be controlled by adjusting the relative orientation between the individual elements.

The study establishes the importance of a new factor, the van der Waals stacking sequence (an unexplored factor in 2D research), while developing electrocatalysts and charge transfer systems based on the 'mix and match' of various atomic layers. We believe that this work will be a paradigm shift in the design and development of cost-effective, light-weight energy devices, and will stand out from existing reports on catalytic cell designs based on atomic layers in terms of the flexibility, transparency and efficacy of the working electrode.

Full details are published in Nanotechnology.