Photo/electrocatalysis of water (H2O) splitting and CO2 reduction reactions is a promising strategy to alleviate the energy crisis and excessive CO2 emissions. For the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and CO2 reduction reaction (CO2RR) involved, the development of effective photo/electrocatalysts is critical to reduce the activation energy and accelerate the sluggish dynamics. Polyoxometalate (POM)‐based compounds with tunable compositions and diverse structures are emerging as unique photo/electrocatalysts for these reactions as they offer unparalleled advantages such as outstanding solution and redox stability, quasi‐semiconductor behaviour, etc. This Minireview provides a basic introduction related to photo/electrocatalytic HER, OER and CO2RR, followed by the classification of pristine POM‐based compounds toward different catalytic reactions. Recent breakthroughs in engineering POM‐based compounds as efficient photo/electrocatalysts are highlighted. Finally, the advantages, challenges, strategies and outlooks of POM‐based compounds on improving photo/electrocatalytic performance are discussed.

Heterogeneous electrocatalysis provides better control of the chemical surroundings of the catalyst's active site for improved performance, offers the possibility of overcoming drawbacks of deactivation caused by aggregation or dimerization in homogeneous condition, and permits the use of benign aqueous solutions. Employing metal−organic frameworks (MOFs) or covalent−organic frameworks (COFs) to support the active molecular catalyst of porphyrin for electrochemical conversion of CO 2 to CO is a promising strategy. We have rationally introduced a 3D highly stable porphyrin-based MOF of PCN-222(Fe) into heterogeneous catalysis through the simple dipcoating method. The composite catalyst PCN-222(Fe)/C (mass ratio = 1:2) exhibited high catalytic performance for electrochemical conversion of CO 2 to CO with 494 mV overpotential (where j = 1.2 mA cm −2 ) and maximum 91% FE CO in a CO 2 -saturated 0.5 M KHCO 3 aqueous solution, achieving a TOF of 0.336 site −1 s −1 . The catalyst was found to retain its crystallinity and stability after 10 h of electrolysis at −0.60 V versus RHE (average FE CO 80.4%; RHE, reversible hydrogen electrode), which generates 334 μmol of CO with the TOF of 0.012 s −1 (0.286 site −1 s −1 ). These results indicate that the PCN-222(Fe)/C has a substantial catalytic effect on the electrochemical reduction of CO 2 due to the combination of the intrinsic activity of the porphyrin molecule, and the promising CO 2 adsorption ability endowed by the conserved porosity, as well as the high conductivity of carbon black.

By introducing the flexible 1,1'-(1,4-butanediyl)bis(imidazole) (bbi) ligand into the polyoxovanadate system, five novel polyoxoanion-templated architectures based on [As(8)V(14)O(42)](4-) and [V(16)O(38)Cl](6-) building blocks were obtained: [M(bbi)(2)](2)[As(8)V(14)O(42)(H(2)O)] [M = Co (1), Ni (2), and Zn (3)], [Cu(bbi)](4)[As(8)V(14)O(42)(H(2)O)] (4), and [Cu(bbi)](6)[V(16)O(38)Cl] (5). Compounds 1-3 are isostructural, and they exhibit a binodal (4,6)-connected 2D structure with Schläfli symbol (3(4) x 4(2))(3(4) x 4(4) x 5(4) x 6(3))(2), in which the polyoxoanion induces a closed four-membered circuit of M(4)(bbi)(4). Compound 4 exhibits an interesting 3D framework constructed from tetradentate [As(8)V(14)O(42)](4-) cluster anions and cationic ladderlike double chains. There exists a bigger M(8)(bbi)(6)O(2) circuit in 4. The 3D extended structure of 5 is composed of heptadentate [V(16)O(38)Cl](6-) anions and flexural cationic chains; the latter consists of six Cu(bbi) segments arranged alternately. It presents the largest 24-membered circuit of M(24)(bbi)(24) so far observed made of bbi molecules and transition-metal cations. Investigation of their structural relations shows the important template role of the polyoxoanions and the synergetic interactions among the polyoxoanions, transition-metal ions, and flexible ligand in the assembly process. The magnetic properties of compounds 1-3 were also studied.

Over the past 200 years, the most famous and important heteroatom Keggin architecture in polyoxometalates has only been synthesized with Mo, W, V, or Nb. Now, the self‐assembly of two phosphate (PO43−)‐centered polyoxo‐titanium clusters (PTCs) is presented, PTi16 and PTi12, which display classic heteroatom Keggin and its trivacant structures, respectively. Because TiIV has lower oxidate state and larger ionic radius than MoVI, WVI, VV, and NbV, additional TiIV centres in these PTCs are used to stabilize the resultant heteroatom Keggin structures, as demonstrated by the cooresponding theoretical calculation results. These photoactive PTCs can be utilized as efficient photocatalysts for highly selective CO2‐to‐HCOOH conversion. This new discovery indicates that the classic heteroatom Keggin family can be assembled with Ti, thus opening a research avenue for the development of PTC chemistry.