clean and sustainable strategy to produce O 2. [1] To date, metallic materials, including Pt, Ir, and Ru, are still the most effective electrocatalytic OER materials owing to their excellent carrier mobilities and high catalytic activities. [2] However, from a commercial perspective, the expensive cost of these precious metals has limited their practical application. [3] As a result, there is an urgent need to find low-cost materials and high-performance electrocatalytic OER materials as substitutes for precious metals. With the advent of graphene, 2D materials have gradually appeared in the field of vision and are considered as good candidates for electrocatalytic OER materials due to their excellent electronic properties and catalytic activities. Previous reports have confirmed that 2D materials have excellent electrocatalytic OER properties, such as MoS 2 , [4] WS 2 , [5] and MXenes. [6] Recently, a new singleelement 2D material, black phosphorus (BP), has been successfully synthesized, which has excellent carrier mobility (1000 cm 2 V −1 s −1 at ten-layer thickness [7]) and good catalytic activity. [8] Therefore, it is widely used in the field of catalysis, especially as an electrocatalytic OER material. [9] For instance, Wang and co-workers [10] adopted a simple method to grow BP nanosheets on a carbon nanotube network and showed excellent electrocatalytic OER performance. Although many studies have reported that BP nanosheets have shown good applications in the field of electrocatalytic OER, its high overpotential and limited catalytic activity still needs to be further improved. Therefore, it is crucial to improve the electrocatalytic OER performance of BP through various strategies. It is well known that the main factors that determine the performance of electrocatalyst OER include the number of catalytic active site, electrical conductivity, and catalytic activity. [3,11] Our previous work has reported [12] that reducing the number of layers of BP nanosheets can expose more reactive sites to enhance its electrocatalytic performance. The experimental results show that with the degree of BP nanosheets, its electrocatalytic oxygen evolution performance is continuously