I am currently writing a review on bismuth-based heterojunctions for electrochemical CO2 reduction reaction. Assuming you are an expert in the field of nanomaterial design and electrocatalysis, please help me to polish the language of my thesis to make it more fluent and more well-written from your professional point of view. Let’s start from here:

4.4.1. Bi subcarbonate-metals
Under the electrochemical testing condition of CO2RR, BOC can be partially reduced to metallic Bi, forming BOC/metal heterojunctions. For example, Zhang et al. found a superior performance of their ultrathin few-layer BOC nanosheet for CO2RR, which is due to the in situ formation of BOC/Bi heterojunction in the potential range from -0.65 to -0.8 V that enhances the electroconductivity of the electrical insulator BOC meanwhile improves the active sites.[40] When totally reducing BOC to metal Bi in a more negative potential, the selectivity of catalyst will in turn decrease. In situ formation of BOC/Bi can be achieved by using other Bi-based precursors. Liang et al. prepared BOC/Bi nanosheets by electroreduction of BiPO4 nanoparticles.[149] The nanosheet morphology with obvious Bi and BOC interfaces can be clearly seen (Figure 15a). The synergistic effect of Bi and BOC at the interface played an important role in changing the adsorption behavior of reaction intermediates and further greatly reducing the activation barrier of the conversion of *OCHO to *HCOOH during CO2 reduction. Some other precursors can be also utilized to construct BOC/Bi heterojunctions. Lin et al. used Bi2S3 to form BOC nanosheets/Bi clusters,[42] while Liu et al. used Bi metal to fabricate BOC@Bi electrode under the CO2RR conditions,[150] both of which provided new ideas for high-performance BOC/Bi heterogeneous catalysts design. Since an electrocatalysis of CO2RR process can convert Bi metal to BOC, by applying In-doped Bi as precursor, a BOC/In heterojunction can be also obtained. [151] The incorporation of In to BOC can further enhance the adsorption ability of intermediates.
4.4.2. Bi subcarbonate-metal oxides
The integration of BOC with metal oxides is another strategy to fabricate high-performance BOC-based heterojunctions. Various metal oxides such as In, Sn, Zn and Ce-based oxides were explored. For example, the BOC/ZnO heterojunction nanoplates materials constructed by Wei et al. display a distinct interface between the lattice fringes of BOC and ZnO (Figure 15b).[65] Such a heterojunction structure facilitates the charge transfer from the Zn to Bi, resulting in an electron-enriched BOC surface for improved CO2 capture and activation. In addition, Wang et al. synthesized a BOC/SnO2 heterojunction,[64] while He et al. developed a BOC/CeOx heterojunction.[60] The synergistic effect of BOC and metal oxides combines the both advantages of the components, which can usually enhance the activation of CO2 molecules and improves electron transfer. Although the above heterojunction structures highly befit CO2RR application, the structural evolution during the electrocatalysis should be paid attention. Wang et al. first prepared a BOC/InOx heterojunction, and then treated it under negative voltages for 1 h.[152] In this way, the BOC/InOx heterojunction was reduced to their corresponding metallic monomers and combined together to form BiIn alloy.
4.4.3. Bi subcarbonate-nonmetal-based materials
Carbon materials are still the most commonly used component to form heterojunction with BOC. Tang et al. used 0D graphdiyne to decorated BOC to facilitate a synergistic effect in catalyst for beneficial CO2 adsorption affinity, faster reaction kinetics and high selectivity for formate.[153] Puppin et al. used 1D CFs to support BOC, which highly enhanced the stability of catalyst during the CO2RR process.[59] 2D reduced graphene oxide was also utilized as support for BOC for a high CO2RR performance by Wang et al.[38] Organics are another important type of nonmetal-based materials to integrate with BOC. Li et al. used L-histidine, a common amino acid molecule of proteins, to decorate BOC catalyst.[154] A thin layer of L-histidine was covered on the BOC nanoplate, which facilitates efficient CO2 adsorption capacity (Figure 15c). On the other hand, Wang et al. introduced S atoms into BOC nanosheets.[155] The lower electronegativity of the substituted S than O enhances the local electron density around Bi active sites, thus effectively enhancing the activity of BOC.

5. Electrochemical CO2RR application
The performance of Bi-based heterojunctions toward electrochemical CO2RR can be evaluated by three aspects, including activity, selectivity and stability. Table S1 summarizes the electrochemical CO2RR performance of different Bi-based heterojunctions. This section will introduce some representative examples with superior activity, selectivity and stability for CO2RR.