The electrochromic (EC) mechanisms of inorganic materials are usually based on reversible cation insertion/extraction or metal deposition/dissolution, which are plagued by ion trapping and dendrite growth, respectively. In this paper, a novel conversion-type electrochromic mechanism is proposed, by making good use of the CuI/Cu redox couple. This CuI-based electrochromic system shows a neutral color switching from transparent and dim grey. By simply increasing the bleaching voltage, I₃⁻/I⁻ redox couple can be further activated. The generated I₃⁻ will readily react with Cu, effectively improving the conversion reversibility and thereby rejuvenating the degraded electrochromic performance. Thanks to the well-designed electrode and the self-healing ability, this conversion electrochromic system achieves rapid response times (t_coloring: 23 s, t_bleaching: 6 s), decant optical modulation amplitude (26.4%), high coloration efficiency (86.15 cm²·C⁻¹), admirable cyclic durability (without performance degradation after 480 cycles) and excellent optical memory ability (transmittance variation < 1% after 10 h open-circuit storage). The establishment of this conversion-type electrochromism may inspire the exploration of novel electrochromic materials and devices.

The enhancements in thermoelectric (TE) performances of p-type skutterudites are usually limited due to the relatively low Seebeck coefficients owing to the higher carrier concentration and more impurity phases induced by inherent structural instability of a Fe-based skutterudite. As shown in this study, alloying engineering of Ni doping at Fe sites in a p-type CeFe_3.8Co_0.2Sb₁₂ skutterudite can not only reduce the impurity phases with high thermal conductivity but also regulate the carrier concentration, and thus significantly increase the Seebeck coefficient. The thermal conductivity was largely suppressed due to the enhanced point defect phonon scattering and decreased hole concentration. As a result, a TE figure of merit ZT of the CeFe_3.5Ni_0.3Co_0.2Sb₁₂ sample reached 0.8, which is approximately 50% higher than that of a Ni-free sample. Appropriate Ni doping can maintain a high ZT at a high temperature by controlling the reduction in a band gap. Therefore, a high average ZT close to 0.8 at 650–800 K for CeFe_3.5Ni_0.3Co_0.2Sb₁₂ was obtained, which was comparable to or even higher than those of the reported Ce-filled Fe-based skutterudites due to the synergistic optimization of electrical and thermal performances. This study provides a strategy to synergistically optimize electrical–thermal performances of the p-type skutterudites by alloying engineering.