Concentration battery - Noutandenchi

A battery in which the battery reaction is not a normal chemical reaction, but rather corresponds to the transfer of material due to concentration differences from one phase to another. There are two main types:
(1) Concentration cell with liquid-liquid interface: A cell consisting of two identical electrode systems with two solution phases in contact with each other, except for the concentration of the solution phase. The transfer of material occurs directly through the interface between the two solution phases. For example, a cell consisting of two silver-silver chloride electrodes with the only difference being the concentration of hydrochloric acid,

Ag|AgCl|HCl( c ^Ⅰ )∥HCl( c ^Ⅱ )|AgCl|Ag

is an example, and the equilibrium voltage U _eq of this battery is given as follows:

Here, tCl is the transport number of the chloride ion, a _± and y _± are the average activity and average activity coefficient of the ion _, respectively, and R , T and F are the gas constant, absolute temperature and Faraday constant, respectively. Therefore, if the ratio of the average activity coefficients is known, the transport number of the chloride ion can be calculated from the measured equilibrium voltage. This type of battery is generally used to measure the transport number of ions.
(2) Concentration cell without liquid-liquid interface: A concentration cell designed so that two phases with different concentrations do not come into direct contact with each other and so that the transfer of substances occurs indirectly through electrode reactions. A cell constructed by inserting electrodes of the same metal with different activity (e.g., amalgam electrodes) into a solution containing the metal ions.

Na amalgam ( c ^I ) | NaCl | Na amalgam ( c ^II )

is one example, and in this case the battery is called an amalgam concentration cell. Also, when gas electrodes are used, similar concentration cells can be made by using different combinations of gas pressures.

Pt|H ₂ ( p ^Ⅰ )|H ₂ SO ₄ |H ₂ ( p ^Ⅱ )|Pt

This type of cell is called a gas concentration cell.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

電池反応が通常の化学反応ではなく，一つの相からほかの相への濃度差による物質移動に相当する電池．大別して2種類がある．
(1)液-液界面を含む濃淡電池：溶液相の濃度が異なる以外はまったく同様な二つの電極系を二つの溶液相があい接するように構成された電池．物質の移動が二つの溶液相界面を通して直接的に起こる．たとえば，塩酸濃度のみが異なる二つの銀-塩化銀電極で構成される電池，

Ag|AgCl|HCl(c^Ⅰ)∥HCl(c^Ⅱ)|AgCl|Ag

はその一例であり，この電池の平衡電圧 U_eq は次のように与えられる．

ここで，t_Cl は塩化物イオンの輸率，a_± および y_± はそれぞれイオンの平均活量および平均活量係数であり，R，T，Fはそれぞれ気体定数，絶対温度およびファラデー定数である．したがって，平均活量係数の比がわかっていれば，この平衡電圧の測定値から塩化物イオンの輸率を算出することができる．一般に，この種の電池はイオンの輸率の測定に用いられる．
(2)液-液界面のない濃淡電池：濃度の異なる二つの相が直接あい接しないように構成され，物質の移動が電極反応を介して間接的に起こるように工夫された濃淡電池．活量の異なる同じ金属の電極(たとえば，アマルガム電極)をその金属イオンを含む溶液中に挿入して構成された電池，

Naアマルガム(c^Ⅰ)|NaCl|Naアマルガム(c^Ⅱ)

はその一例であり，この場合の電池をアマルガム濃淡電池という．また，ガス電極を用いる場合には気体の圧力が異なる組合せによっても同じような濃淡電池ができる．

Pt|H₂(p^Ⅰ)|H₂SO₄|H₂(p^Ⅱ)|Pt

この電池をガス濃淡電池という．

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