The present work is devoted to the search for new electrode materials for low-temperature thermionic energy converters (TECs). As shown, the carbon nanostructures (СNS) adding to pure powdered titanium in an amount of 3–9% wt. and their subsequent mechanical mixing leads to the formation of composites that acquire new qualities that were not present in any of their original pure constituents. Thus, the significant changes in the mechanical and electrical characteristics of composites are observed. For example, the electrical conductivity is changed up to 2 orders in initial state of composites as well as its maximum values after samples’ compaction are increased (1.6–5 times) in comparison with both the pure Ti powder and the pure thermally extended graphite (TEG) in corresponding compression states. Such changes are caused by the presence of contacts between the metal particles and the CNS in the metal–nanocarbon composites and, accordingly, the possibility of the transition of free charges, including hot charges, from the metal to the CNS. This allows the use of such composites as cathode materials for low-temperature thermionic energy converters (TECs). For such TECs the high nonequilibrium state of electronic subsystem as well as the electronic structure and surface geometry are important, for example, a significant aspect ratio for separately located surface elements, $i.e.$ the thin needles of carbon nanotubes and thin blades of graphene planes of TEG, protruded from composite surface. The electron emission properties of the Ti–TEG composite materials under the conditions of their illumination by concentrated sunlight are investigated. Thus, at temperatures of 170–350°C, which are 3–5 times lower than the operating temperatures of traditional TECs made with refractory metals, a voltage and, for the first time, a constant current in a closed electric circuit are observed without applying an additional external difference of potentials. As found, in addition to decreasing of contribution of thermal electron emission mechanism for benefit of autoelectronic one, the influence of ionized residual gases in the vacuum chamber, especially caesium ions, plays a significant role in reducing the electron work function from such composite nanostructures and compensating space charge. As revealed, under the influence of concentrated solar radiation a change in the morphology of the composite surface is occurred, $i.e.$ on the Ti particles a large number of new CNS with a diameter of 20–80 nm are formed. This new type of CNS also acts as sources of electronic emission and increases the cathode emission efficiency and decreases its operating temperature due to their small thickness and the negative electron affinity of carbon in the $sp^3$-hybridized state.