Blue energy conversion, where the chemical energy stored in salinity gradients can be converted into electricity with ion-selective nanochannel membranes, has considered to be one of the most promising renewable energies. Conventional understanding on this energy suggests that as to largely reduce the resistance, ultrashort channel membranes are required to gain high-energy output. To understand the channel-length-dependent blue energy conversion in detail, we engineered a series of highly ordered and uniform ~23.0 nm in diameter alumina nanochannel membranes with various lengths. Most anomalously, our experiments however show that for sufficiently short nanochannels, the shorter the channel length, regardless of surface charge nature, the smaller the generated power, violating the past understanding. The anomalous channel-length-dependent blue energy conversion is well supported by our rigorous model. The modeling reveals that ultrashort nanochannels will induce the significant ion concentration polarization effect, which appreciably undermines effective salinity ratio and ion selectivity in the nanochannel. If this effect dominates, the nanofluidic osmotic power turns into a decrease with decreasing channel length. Both the experimental and theoretical results reported consistently highlight the importance of osmotic ion transport especially in ultrashort nanochannels, and this finding shed light on the design of high-efficiency blue energy harvesters.

蓝色能量转换被认为是最有希望的可再生能源之一，其中以盐分梯度存储的化学能可以通过离子选择性纳米通道膜转换为电能。对这种能量的常规理解表明，为了大大降低电阻，需要超短通道膜来获得高能量输出。为了详细了解通道长度相关的蓝色能量转换，我们设计了一系列高度有序且均匀的〜23.0 各种长度的直径为200纳米的氧化铝纳米通道膜。然而，最反常的是，我们的实验表明，对于足够短的纳米通道，无论表面电荷性质如何，通道长度越短，产生的功率就越小，这违反了过去的理解。我们严格的模型很好地支持了异常的与通道长度相关的蓝色能量转换。该模型表明，超短纳米通道将引起显着的离子浓度极化效应，从而显着破坏纳米通道中的有效盐度比和离子选择性。如果这种作用占优势，则随着通道长度的减小，纳米流体的渗透力会降低。