The most widely used electrode materials are porous carbons. They not only fulfil these three conditions but are also cheap, with various synthetic approaches developed to give a range of with partial d-shell occupation, such as Co(II/III), Cu(I/II) or Ni(II/III). Alternatively, traditional carboxylate ligands can be substituted by a large variety of π-conjugated linkers that promote charge transport, such as triphenylamine or tetrathiafulvalene. MOFs can be classified based on the dimensionality of the connectivity between building blocks in their crystal structures: from one-dimensional (1D) chains, to stacked two-dimensional (2D) sheets, and three-dimensional (3D) networks (Fig. ). The dimensionality of MOFs is important because it impacts the accessible pore structure and internal surface area. Fig. : Design strategies for metal-organic frameworks (MOFs) depending upon spatial arrangements of both inorganic and organic constituents. Each MOF has been successfully synthesised . The pore structure is coloured in blue.