Cost-Effective Catalytic 3D-Junction Bipolar Membranes Enabled by MOF/GO Nanocomposite Junction Modifiers for Water Splitting

Although bipolar membrane (BPM) water splitting has attracted much attention as an alternative to existing water-splitting technologies, BPMs also suffer from a high overpotential required for water splitting. To reduce the high water-splitting overpotential in BPMs, we designed nanocomposite catalysts consisting of GO and a metal-organic framework (MOF) by optimizing the GO-to-MOF ratio, considering the following factors: (i) it is advisable to make the most of the water dissociation active sites by minimizing the overlap among MOF nanoparticles incorporated onto the GO platelet, (ii) GO was generally more expensive than the MOF products surveyed, and (iii) substituting some of the GO with MOF can reduce acidic wastewater generation associated with GO preparation. Among several GO-to-MOF ratios, the nanocomposite catalyst consisting of GO and MOF at a ratio of 1:2 (G1M2) provided more accessible active sites for water dissociation due to its favorable architecture for the transport of diffusing species, leading to the lowest water dissociation overpotential. As a result, the 3D-junction BPM containing G1M2 successfully achieved a transmembrane voltage of 0.945 V at 100 mA/cm2, which is within 12% of the thermodynamic minimum potential (0.83 V) required for water splitting.