It is believed that a TiN coating can increase the electrical conductivity, and consequently the performance, of an electrode. In this work, a simple one-step synthesis of nitrogen- and TiN-modified Li4Ti5O12, i.e. solid-state reaction of Li2CO3 and TiO2 anatase in an ammonia-containing atmosphere, is introduced. The reducing ammonia atmosphere could cause the partial reduction of Ti4+ to Ti3+ and the doping of nitrogen into the Li4Ti5O12 lattice, in addition to the formation of the TiN phase. By controlling the ammonia concentration of the atmosphere and using a slight Ti excess in the reactants, Li4Ti5O12, nitrogen-doped Li4Ti5O12, or TiN-coated nitrogen-doped Li4Ti5O12 were obtained. Both the electrical conductivity and the TiN thickness were closely related to the ammonia concentration in the atmosphere. Synthesis under reducing atmosphere also resulted in powders with a different plate shape particulate morphology from that synthesized in air, and such plate-shape powders had an ultrahigh tap density of ∼1.9 g cm−3. Interestingly, the formation of TiN was not beneficial for capacity improvement due to its insulation towards lithium ions, unlike the nitrogen doping. The sample prepared under 3% NH3–N2, which was free of TiN coating, showed the best electrode performance with a capacity of 103 mA h g−1 even at 20 C with only 3% capacity decay after cycling 100 times.

Nowadays, there is a doubt about the electrochemical contribution of silver current collector on the oxygen reduction reaction (ORR) over oxide electrodes in SOFCs since many reports have demonstrated that the modification of porous oxide electrodes with nano-size silver can obviously improve the electrocatalytic activity for ORR. In this study, the electrochemical contribution of silver current collector to the performance of Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) electrode on Sm0.2Ce0.8O1.9 (SDC) electrolyte for ORR was specifically investigated. The active layer of BSCF electrode was found to be around 25 μm by using both silver and gold current collectors. Much better performance was demonstrated by using silver current collector, both from symmetric cell and single cell tests. However, EIS of silver on SDC electrolyte demonstrated the silver alone as electrode actually had poor performance for ORR. In addition, SEM-EDX confirmed that there was no silver diffused from the current collector layer to modify the porous BSCF electrode. Interestingly, the activation energy for oxygen reduction over BSCF electrode was reduced by applying silver current collector. We then proposed a mechanism to explain the improved electrochemical performance of BSCF electrode by considering the high activity of silver for oxygen surface diffusion.Highlights► The active layer of BSCF electrode was found to be around 25 μm. ► Ag current collector showed a beneficial effect on ORR of BSCF on SDC. ► Ag current collector can improve oxygen surface exchange kinetic of BSCF.

It is believed that a TiN coating can increase the electrical conductivity, and consequently the performance, of an electrode. In this work, a simple one-step synthesis of nitrogen- and TiN-modified Li4Ti5O12, i.e. solid-state reaction of Li2CO3 and TiO2 anatase in an ammonia-containing atmosphere, is introduced. The reducing ammonia atmosphere could cause the partial reduction of Ti4+ to Ti3+ and the doping of nitrogen into the Li4Ti5O12 lattice, in addition to the formation of the TiN phase. By controlling the ammonia concentration of the atmosphere and using a slight Ti excess in the reactants, Li4Ti5O12, nitrogen-doped Li4Ti5O12, or TiN-coated nitrogen-doped Li4Ti5O12 were obtained. Both the electrical conductivity and the TiN thickness were closely related to the ammonia concentration in the atmosphere. Synthesis under reducing atmosphere also resulted in powders with a different plate shape particulate morphology from that synthesized in air, and such plate-shape powders had an ultrahigh tap density of ∼1.9 g cm−3. Interestingly, the formation of TiN was not beneficial for capacity improvement due to its insulation towards lithium ions, unlike the nitrogen doping. The sample prepared under 3% NH3–N2, which was free of TiN coating, showed the best electrode performance with a capacity of 103 mA h g−1 even at 20 C with only 3% capacity decay after cycling 100 times.