Capacitance Catalysis: Positive and Negative Effects of Capacitance of Mo₂C in Photocatalytic H₂ Evolution

Abstract

A non-noble metal cocatalyst with capacitance is cost-effective and has excellent photocatalytic H2 evolution performance for water splitting. But the intrinsic action of capacitance is unclear. Here, by controlling the capacitance of Mo2C, we reported a volcanic curve relationship between the photocatalytic activity of Mo2C/CdS and the capacitance of Mo2C. At the middle capacitance of 18.95 F/g of Mo2C-a4, Mo2C-a4/CdS exhibits the best H2 evolution activity of 5560 μmol/g/h. When Pt is introduced on the surface of Mo2C, the photocatalytic activity of (Pt/Mo2C-a4)/CdS is further enhanced to 8090 μmol/g/h. Comparing the activities between (Pt/Mo2C)/CdS and Mo2C/CdS with the capacitance of Mo2C, the activity ratio and difference values increase and finally reach a plateau with the increasing capacitance. Electrochemical and photoelectrochemical studies demonstrate that the capacitance of Mo2C has dual opposite effects (positive and negative) in photocatalytic reactions. The capacitance can capture electrons and store them, thereby enhancing the separation efficiency of photoexcited carriers of CdS. However, overlarge capacitance constrains the stored electrons and prevents them from releasing, thus decreasing the cocatalytic efficiency, which can be resolved in some degree by introducing some Pt on Mo2C. This work elucidates the dual effects of capacitance and puts forward the concept of capacitance catalysis.

A bifunctional hierarchical core–shell Mo2C@ZnIn2S4 Schottky junction for efficient photocatalytic H2-evolution integrated with valuable furfural production

“…Besides, Mo 3d and S 2s possess similar binding energy regions, so they are easily covered by the strong S 2s signal. [43][44][45] Specifically, the peaks of Zn 2p, In 3d, and S 2p exhibit a positive shift in 1.5%MC@ZIS compared to ZIS, and the binding energies of C 1s of 1.5%MC@ZIS are negatively shifted as compared with those of pure MC. In this circumstance, a strong electronic coupling effect and charge redistribution between MC particles and ZIS nanosheets are established, which will induce the electrons to spontaneously flow from the ZIS to the MC component upon the formation of the Schottky contact.…”

“…Two peaks centered at 231.7 and 228.6 eV arise from the characteristic Mo 3d 3/2 and Mo 3d 5/2 of Mo-C in MC, and the other two peaks at 235.7 and 232.9 eV could be ascribed to the Mo 3d 3/2 and Mo 3d 5/2 of Mo-O in MoO 3 , possibly caused by exposure to air, which is a common phenomenon in previously reported Mo 2 C based-catalyst systems. [42][43][44] No obvious Mo 3d XPS signals could be observed in 1.5%MC@ZIS (Fig. S5 †), which might be because of the relatively low content of MC in the 1.5% MC@ZIS heterojunction.…”

Effects of Alternating Magnetic Fields on the OER of Heterogeneous Core–Shell Structured NiFe2O4@(Ni, Fe)S/P

“…However, the alternating electric field, generated by the AMF, causes ion enrichment at the two interfaces. 53 Capacitance had the ability to constrain charge transfer 57 and would maintain a high concentration of OH − in the bilayer, which did not favor the adsorption of OH − from the solution into the bilayer as a negative effect. In summary, there is no contradiction with the Grotthuss mechanism.…”

Ultrafast charge separation in a WC@C/CdS heterojunction enables efficient visible-light-driven hydrogen generation

“…3(a and b), the binding energies located at 405.2 and 411.9 eV correspond to Cd 3d 2/5 and Cd 3d 3/2 , [34][35][36] respectively. Meanwhile, the binding energies of 161.6 and 162.8 eV were attributed to S 2p 3/2 and S 2p 1/2 , [37][38][39] respectively. The binding energies of Cd and S in the 7 wt% WC@C/CdS photocatalyst elements both showed a slightly high shift as compared with pristine CdS.…”