Fig. 2

Anti-gradient ion transport. a Time traces of photocurrent under concentration gradient. Light illumination (100 mW cm⁻²) was on the left 1/3 of the GOM. When C_L/C_R = 10/1, the ionic current goes across the zero line, and further increases in the reverse direction, showing anti-gradient ion transport. But when the concentration gradient was too high (e.g., C_L/C_R = 20/1) or in the reverse direction (C_L/C_R = 1/20), no ionic current reversion was found. b Photo-induced variations in K⁺ concentration and corresponding ion pumping rates measured by ICP-OES. After light illumination for 180 s, C_high further arises, while C_low falls down, showing anti-gradient ion transport. Error bars denote standard deviation. c Photocurrent against different concentration gradients and with varied light intensities. The dashed line indicates the diffusion current (I_diff). When the magnitude of the photocurrent is larger than I_diff, anti-gradient ion transport can be found. Otherwise, the ion transport is governed by the concentration gradient. d Pumping rates for different ionic species against 10-fold concentration gradient. The gray area indicates the below-detection limit of the measurements. The concentration change for Fe³⁺, Cr³⁺, [Ru(bipy)₃]²⁺ was not effectively detected