1. Department of Physics and Astronomy, University of Bologna, Viale Berti Pichat 6/2, 40127 Bologna, Italy.
2. INFN-Bologna, Viale Berti Pichat 6/2, 40127 Bologna, Italy.
3. Department of Industrial Engineering, University of Trento, Via Sommarive 9, I-38123 Povo, Trento, Italy.
4. INFN-TIFPA, Via Sommarive 14, I-38123 Povo, Trento, Italy.
5. INFN-Florence, Via G. Sansone 1, 50019 Sesto Fiorentino, Florence, Italy.
6. Department of Chemistry and Center for Applied Energy Research, University of Kentucky, Lexington, KY 40506, USA.