Co(III)离子在二氧化铅电极上的阳极形成

文献上曾报导过Co(Ⅱ)离子具有加速PbO_2电极上氧阳极析出过程的作用,并表明当Co(Ⅱ)离子存在时,氧的析出过程有可能通过表面吸附的高价钴氧化物氧化水分子而形成.本文通过浓硫酸溶液中Co(Ⅱ)阳极氧化为Co(Ⅲ)以及O_2阳极析出动力学的研究,表明了O_2的析出和Co(Ⅲ)的形成是通过吸附在电极表面的高价钴(Ⅳ)的OH 基配合物分别氧化水分子和Co(Ⅱ)离子形成的,它与Cr(Ⅲ)、Mn(Ⅱ)离子的阳极氧化过程相类似,而不是通过Co(Ⅱ)离子直接放电形成的.本文利用文献所述的研究方法.在固定硫酸浓度(3.4mol·kg~(-1))下,研究CoSO_4浓度(0.05—0.35mol·drn~(-3))对于O_2和Co(Ⅲ)阳极形成过程分别的影响.在固定CoSO_4(0.2mol·

ANODIC FORMATION OF THE Co~(3+) ION AT PbO_2 ANODE IN CONCENTRATED H_2SO_4 SOLUTIONS

The kinetic data related respectively to Co~(3+) anodic formation and O_2 anodic evolution at PbO_2 anode in 3.4 mol·kg~(-1) H_2SO_4+x mol·dm~(-3) COSO_4 (x=0.0501-0.350) and 0.2 mol·dm~(-3) CoSO_4+x mol·kg~(-1) H_2SO_4 (x=1.556-9.110) solutions were obtained by method of resolving the steady-state polarization curve. Steady-state φ～lgi relationships for Co~(3+) anodic formation reaction Tafel slope is close to 2.303RT/βF, whereas for O_2 anodic evolution it is close to 2.303RT/2βF (with β(?)0.5). It is shown by experiment that the anodic formation of Co~(3+) and O_2 anodic evolution at PbO_2 anode in H_2SO_4 solutions are described by the equations:i_1(O_2)=k_1a_W~4Co~(2+)]exp2βφF/RTi_2(Co~(3+))=k_2a_WCo~(2+)]~(1.5)expβφF/RTThe experimental results may be explained by adopting the following scheme of electrode reactionsM+Co(H_2O)_6~(2-)+4H_2O→MCo(OH)_4(H_2O)_(2,ad)+4H_3O~++2e2MCo(OH)_4(H_2O)_(2,ad)+2H_2O→O_2+2MCoO(H_2O)_(5,ad)MCoO(H_2O)_(5,ad)+2H~+=M+Co(H_2O)_6~(2+)MCo(OH)_4(H_2O)_(2,ad)+Co(H_2O)_6~(2+)→2Co(OH)_2(H_2O)_4~++MCo(OH)_2(H_2O)_4~++2H~+=Co(H_2O)_6~(3+)where M is an adsorption site on the PbO_2 anode.