Fig. 2

Average values of a current (mA) and b power density (mW m−2) were analyzed throughout the operation period (pH 7.0: open circles, pH 5.5: open squares, and pH 4.0: open triangles)
Average values of a current (mA) and b power density (mW m−2) were analyzed throughout the operation period (pH 7.0: open circles, pH 5.5: open squares, and pH 4.0: open triangles)