Ca^(2+)置换La^(3+)的量对La-Ca-Co-O氧还原催化活性和电导率的影响

Effect of amount of Ca^(2+) substituting La^(3+) on catalysis activeness of La-Ca-Co-O to oxygen reduction and its conductivity

为了优化钙钛矿型La1-xCaxCoO3成分,研究了不同量Ca2+置换La3+后,La1-xCaxCoO3催化氧还原反应的交换电流密度和其自身电导率的变化规律。采用溶胶-凝胶法制备了La1-xCaxCoO3粉体,通过XRD检测发现当Ca2+置换量较大时,会析出Ca2Co2O5。在6mol/L的KOH溶液中,通过线性扫描伏安技术测定了催化剂催化氧还原反应的极化特性;通过Tafel技术测定了其催化氧还原反应的交换电流密度。采用粉末压片和直流电路测定了催化剂的表观电导率。结果表明,随着Ca2+置换量增加,La1-xCaxCoO3催化氧还原反应的交换电流密度先增高、然后又降低,在x=0.5～0.6,交换电流密度达到最大,约为0.1382A/m2;表观电导率也是先增大,后又减小,同样在x=0.5～0.6,表观电导率达到最大,约为0.2930Ω-1.m-1。交换电流密度和表观电导率随Ca2+置换量的变化趋势基本一致。

In order to optimize composition of perovskite-type La1-xCaxCoO3, the change mechanism of exchange current density of La1-xCaxCoO3 catalyzing oxygen reduction and its conductivity is investigated when La3＋ is substituted by varied amount of Ca2＋. La1-xCaxCoO3 powder is prepared through sol-gel method, and its phase structure is checked by XRD. It shows that phase Ca2Co2O5 will form when amount of Ca2＋ is bigger. The electrochemical effective area of powders with different amount of Ca2＋ is determined through potential step technology. The electrochemical polarization of powder for catalyzing oxygen reduction is investigated by linear scan voltammetry technology in 6mol/L KOH solution. And then, the exchange current density during catalyzing oxygen reduction is measured through Tafel technology. The apparent conductance of powder pellet is measured by direct current circuit method. Results show that the exchange current density of La1-xCaxCoO3 catalyzing oxygen reduction increases with Ca2＋ amount at first, and then decreases again. The exchange current density reaches its maximum, about 0. 1382A/m2, at x=0. 5-0. 6. In the same way, the apparent conductivity changes according to similar trend. It reaches the maximum, about 0. 2930Ω-1·m-1, at x=0. 5-0. 6. The change trend of exchange current density and apparent conductivity is consistent essentially with Ca2＋ replacing La3＋ in La1-xCaxCoO3 lattice.