  We present a comprehensive first-principles Density Functional Theory (DFT)
analyses of the interfacial strength and bonding mechanisms between crystalline
and amorphous selenium(Se) with graphene(Gr), a promising duo for energy
storage applications. Comparative interface analyses are presented on amorphous
silicon(Si) with graphene and crystalline Se with aluminum(Al) substrate. The
interface strength of monoclinic Se (0.43 J/m2) and amorphous Si with graphene
(0.41 J/m2) is similar in magnitude. While both materials (c-Se, a-Si) are
bonded loosely by van der Waals (vdW) forces over graphene, interfacial
electron exchange is higher for a-Si/Gr. This is further elaborated by
comparing potential energy step and charge transfer (delta q) across the
graphene interfaces. The delta q for c-Se/Gr and a-Si/Gr are 0.3119 e-1 and
0.4266 e-1, respectively. However, the interface strength of c-Se on the 3D Al
substrate is higher (0.99 J/m2), suggesting stronger adhesion. The amorphous Se
with graphene has comparable interface strength (0.34 J/m2), but electron
exchange in this system is slightly distinct from monoclinic Se. The electronic
characteristics (density of states analysis) and bonding mechanisms are
different for monoclinic and amorphous Se with graphene and they activate
graphene via surface charge doping divergently. Our findings highlight the
complex electrochemical phenomena in Se interfaced with graphene, which may
profoundly differ from their 'free' counterparts.
