Manipulating Coordination-Unsaturated H-Bond toward Efficient Electrochemical Hydrogen Isotope Separation

O) in nuclear reactors and isotopic tracing, a promising advanced separation method by water electrolysis is urgently required to lower energy consumption. Nevertheless, the cleavage of the O-H and the O-D covalent bonds occurs almost simultaneously due to the similar bond dissociation energies (BDEs), resulting in poor H/D separation efficiency. Herein, the discrepancy in BDEs of the O-H and O-D bonds is magnified by introducing a series of organic additives with different Gutmann donor numbers to tune the H-bond network and further promote the H/D isotope separation coefficient. Specifically, the difference in BDEs between the O-H and the O-D bonds is amplified by more than 6 times (from 0.95 to 6.24 meV), which is attributed to a moderate H/D-bond network induced by an increased proportion and spectral red-shift of the dominant coordination-unsaturated H/D-bond in the sulfolane (SUL) additive system. Consequently, the system achieves excellent H/D isotope separation performance, with gas-liquid separation coefficients reaching 17.28. The D atomic fraction is enriched to 8.8% with a feeding of 5.0% D after 4 h of electrolysis at room temperature. This modulation strategy of the H/D-bond network establishes an effective pathway for electrochemical H/D separation.