Co-optimization of g-C3N4 with prolonging exciton lifetime strategy and co-catalyst strategy for enhanced photocatalytic H2 evolution activity

In this work, the photocatalytic activity of g-C3N4 is co-optimized for the first time using a strategy of prolonging exciton lifetime and a co-catalyst strategy. Amorphous CoB nanoparticles are loaded on OCN-K-CN, which is an O, K doped g-C3N4 material with van der Waals heterojunctions inside. The optimized OCN-K-CN-CoB sample, containing 12 wt% CoB and 1.25% K2SO4 in precursors, show photocatalytic H2 evolution rate approximately 27 times higher than that of GCN. The mechanism of co-optimization is detailedly investigated through comparative experiments on light absorption, charge separation performance, and HER activity, with optimization strategy and CoB loading ratio as controlled variables. New roles of the two strategies have been revealed: "flux-limited reduction activity sites" for CoB and ''buffer-enhancer'' for OCN-K-CN. These new roles illustrate a hidden relationship between the optimizing effects of the two strategies and can explain a surprising advantage of this co-optimization: achieving near-optimal hydrogen evolution activity with significantly reduced co-catalyst loading ratio. [Display omitted] The left part of the picture shows the contribution of OCN-K-CN strategy and CoB strategy in the H2 evolution reaction rate of co-optimized OCN-K-CN-CoB sample with different CoB loading ratios. The varying contribution levels of the two strategies with different CoB loading ratio imply the hidden relationship between them. The left part shows the photocatalytic H2 evolution mechanism of the co-optimized OCN-K-CN-CoB sample. •Boost g-C3N4's photocatalytic H2 evolution rate by 27 times with OCN-K-CN structure and CoB co-catalyst.•Prolong exciton lifetime and co-catalyst strategies are synergistically combined for the first time.•Contribution of each strategy on light harvest, charge transfer and HER reaction are revealed.•Newly discovered role of the OCN-K-CN structure in co-optimization as a "buffer enhancer."•Newly discovered role of the CoB in co-optimization as "flux-limited reduction activity sites."