Unitary graphene matrix composites containing carbon or graphite fillers

A unitary graphene matrix composite comprising:

• (a) A unitary graphene matrix containing closely packed and chemically bonded graphene planes having an inter-graphene plane spacing of 0.335 to 0.40 nm and an oxygen content of 0.001% to 10% by weight, which unitary graphene matrix is obtained from heat-treating a graphene oxide gel at a temperature higher than 100° C. and contains no discrete graphene platelets derived from said graphene oxide gel;
• and
• (b) A carbon or graphite filler phase selected from a carbon or graphite fiber, carbon or graphite nano-fiber, carbon nano-tube, carbon nano-rod, meso-phase carbon particle, meso-carbon micro-bead, exfoliated graphite flake with a thickness greater than 100 nm, exfoliated graphite or graphite worm, coke particle, needle coke, carbon black or acetylene black particle, activated carbon particle, or a combination thereof;
• wherein said carbon or graphite filler phase occupies a weight fraction of 0.01% to 99% based on the total composite weight and said carbon or graphite filler phase is in a particulate, filamentary, or rod-like form dispersed in said unitary graphene matrix.