Study on Uranium Redox-flow Battery with High Energy Efficiency

截至1999年底，全世界已储存了1.2亿多吨贫铀，发展其和平利用是一个重要问题。锕系化学最突出的性质之一是III/IV价和V/VI价之间的可逆电极反应。如果利用这一特性，即使与现有的钒电池相比，也有望获得具有高能效的氧化还原液流电池。2003年对能源效率进行了理论研究。在钒电池中，正极反应VO_2^++4H^++e^-→VO^<2+>+2H_2O是伴随氧解离的内球反应。当电流密度为70mA/cm2时，由于活化过电位的影响，放电和充电循环中损失了16%的能量。相反，由于两种电解质在锕系元素中的反应都很迅速，在Np的情况下，激活过电位造成的能量损失保持在2%。我们构建了Np电池，并通过充放电实验对其能量效率进行了研究。2004年，分别以U(V)和U（III）为正极和负极电解质的铀电池建成并进行了论证。结果表明，该铀电池的放电量足以满足电机转子的旋转需要。另一方面，U(V)和U（III）的浓度分别在放电状态和充电状态下处于半衰减期，衰减时间约为几个小时。由于这意味着铀配合物的稳定性不够，2005年，对迄今为止仅研究过的U(V)和U（III）配合物进行了研究。因此，成功制备了半衰期超过半年的U(V)配合物溶液。同时成功制备了U（III）二胺配合物，并在溶液中半衰期为11小时，研究了U(III)/U（IV）的电极反应。

More than 120 million tons of depleted uranium has been stored all over the world even at the end of 1999, and an development of its peaceful utilization is an important issue. One of the most outstanding property of actinide chemistry lies in reversible electrode reaction between III/IV valences, and V/VI valences. Provided this character is used, a redox-flow battery possessing high energy efficiency even if comparing with the existing vanadium battery is expected.Energy efficiency was theoretically studied in 2003. In vanadium battery, positive electrode reaction VO_2^++4H^++e^-→VO^<2+>+2H_2O is inner-sphere reaction accompanied with dissociation of oxygen. Due to activation overpotential 16% of energy are lost in discharge and charge cycle at current density 70mA/cm2. In contrast, since reactions of both electrolytes are rapid in actinides, loss of energy by activation overpotential remains in 2% in the case of Np. We constructed the Np battery and energy efficiency was studied through charge and discharge experiments.In 2004, uranium battery which equips with U(V) and U(III) as positive and negative electrolytes, respectively, was constructed and demonstrated. As a result, this uranium battery discharged electricity enough for rotating rotor of motor was confirmed. On the other hand, concentration of U(V) and U(III) in discharged and charged state, respectively, decays in half decay period for around several hours. Since this means that stability of uranium complex is not enough, in 2005, investigation of U(V) and U(III) complex, which were merely studied up to present, were performed. Consequently, preparation of U(V) complex solution with the half life exceeding a half year was successful. Also a preparation of the U(III) diamide complex was successful and during its half life of 11 hours in solution, electrode reaction of U(III)/U(IV) was studied.