Carbon derived from hair is interesting because it has good electrocatalytic activity due to the existence of innate heteroatom dopants especially nitrogen and sulfur. In this study, a carbon catalyst containing high nitrogen contents (9.47 at.%) was fabricated without using any harsh chemicals. Moreover, the carbonization temperature was only 700°C. Carbonized hair/ PEDOT:PSS composites (C x P) with varied carbon contents from x = 0.2 to 0.8 g were tested as a counter electrode (CE) for a dye-sensitized solar cell (DSSC). This type of DSSC CE has scarcely been investigated. A DSSC with a C 0.6 P CE provides the best efficiency (6.54 ± 0.11%) among all composite CEs because it has a high fill factor (FF) and a high short-circuit current density (J sc ). The efficiency of DSSC with C 0.6 P CE is lower than Pt's (7.29 ± 0.01%) since the Pt-based DSSC has higher FF and J sc values. However, C 0.6 P is still promising as a DSSC CE since it is more cost-effective than Pt.

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Copper samarium co-doped ceria (CSDC) (Cu0.01Sm0.19Ce0.80O2−δ) nanoparticles were synthesized via a sol-gel auto-combustion of metal nitrates without a complexing agent (DI) and with tartaric acid (TA) or citric acid (CA). The solid oxide formation of CSDC/DI corresponds to the endothermic stage, whereas that of CSDC/TA and CSDC/CA matches the exothermic stage caused by the decomposition of the metal cross-linking and carbon combustion. The cross-linking occurs more extensively in the CA case as more heat is released in CA than in the TA route. The as-synthesized morphology of CSDC/DI reveals both layered structures and small agglomerated particles, whereas CSDC/TA and CSDC/CA show dense xerogel and porous xerogel, respectively. The cubic fluorite structure for calcined CSDCs was confirmed by XRD. From Raman analysis, calcined CSDC/CA has the lowest amount of copper segregation and the highest relative total oxygen vacancy concentration [ V O • • ]total, whereas calcined CSDC/DI has the highest amount of copper segregation and the lowest [ V O • • ]total. For all samples, copper segregation promotes densification, albeit to varying degrees. The relative densities of CSDC/DI, CSDC/TA, and CSDC/CA pellets are 82.8 ± 2.4%, 95.5 ± 1.8%, and 97.8 ± 0.9%, respectively. The sintered CSDC/DI has the lowest density because some copper segregates and liquid copper in interparticle spaces could evaporate earlier than samples containing a complexing agent, whereas sintered CSDC/CA has the highest density because Cu could slowly diffuse from the Cu-Sm-Ce solid solution to grain boundary regions and then precipitate as CuO. The specific grain boundary conductivity is predominantly influenced by CuO along grain boundaries, which reduces specific grain boundary conductivity and increases the enthalpy of association (ΔHa) at 250–350°C; however, it rarely impacts total grain boundary conductivity at temperatures higher than 400°C. CSDC/CA has slightly higher total conductivity than CSDC/TA despite having more CuO segregation because it has higher density and V O • • .

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A copper samarium co-doped ceria (CSDC) (Cu0.01Sm0.19Ce0.80O2-δ) nanoparticles were synthesized via a sol-gel auto-combustion of metal nitrates with two different complexing agents including tartaric acid (TA) and citric acid (CA). A reference sample was metal nitrates in deionized water (DI). TGA/DSC of gels reveals endothermic reaction for CSDC/DI but exothermic behavior for CSDC/TA or CSDC/CA during oxide formation. The CA route exhibits the highest energy release since it has extensive formation of metals-citrate. From SEM, the as-synthesized morphologies of DI, TA and CA routes show porous sheet-like, fluffy-like and foamy-like structure, respectively. XRD patterns of calcined CSDCs denote a cubic fluorite structure. The average particle sizes from TEM vary in the range of 30-32 nm. The relative oxygen vacancy (VO) concentrations for calcined and sintered CSDCs from Raman analysis are as follow; CSDC/CA>CSDC/TA>CSDC/DI. Moreover, segregation of (Ce and/or Sm)2O3 and CuO can be observed in Raman spectra for calcined and sintered CSDCs. The oxides of copper segregate mostly in sintered CSDC/CA. The XPS results confirm that Ce3+/Ce4+ coexist, and in addition, the Ce3+ represent Ce3+-VO and/or Ce2O3 segregation. The Ce3+ in sintered CSDCs suggest the existence of Ce3+-VO for CSDC/DI and CSDC/CA; however, Ce3+ implied coexisting of Ce3+-VO and Ce2O3 segregation for CSDC/TA. The relative densities of sintered CSDC/DI, CSDC/TA and CSDC/CA are 82.78%, 95.51% and 97.98%, respectively. The enthalpy of association increases with the increasing of porosity and metal oxide segregation. Segregation of CuO increases CSDC/CA’s association enthalpy at low temperature but it does not affect high temperature conductivity of CSDC/CA. The high total conductivity of 0.0271 S/cm was achieved for CSDC/CA at 600 °C.