  Graphene has drawn wide attention due to its exceptional thermal conductivity
but complete understanding of thermal characteristics of polycrystalline
graphene is still elusive to date. For the first time, herein, we have
systematically studied the effect of temperature on the thermal conductance
behavior of polycrystalline graphene for a range of grain sizes and grain
boundary types, by using non-equilibrium molecular dynamics simulations. It is
noted that increasing the tempera-ture remarkably enhances thermal boundary
conductance (Kapitza conductance) across grain boundaries while it deteriorates
thermal conductivities of defect-free grain regions, regardless of grain sizes
and grain boundary types. This enhancement effect becomes more important for
smaller grain sizes and higher temperatures, whose normal adverse effects on
the heat transfer are thus ideally counterbalanced, making total thermal
conductivity rather robust against the temperature increment for sufficiently
small grain sizes. Upon heating from 300 to 500 K, thermal conductivity of
graphene with maximally tilted grain boundaries decreases only by 9 % for a
grain size of 50 nm in contrast to the decrease of 28 % for 250 nm, and
further, it even increases below 30 nm. We presented quantitative mapping of
its (grain, grain boundaries, and total) thermal conductivi-ties in terms with
grain sizes and temperatures, providing a guideline for graphene-based thermal
engineering and suggesting novel defect-based thermal architectures as well.
