Exploring Highly Efficient Oxygen Evolution Reaction Electrocatalysts

Black Phosphorus (Credit: smart-elements.com)

The presence of oxygen evolution reaction (OER) has been confirmed to be crucial significant in the progress of various energy conversion devices such as energy storage and water splitting. However, overall electronic transfer kinetics of water splitting has been greatly limited due to the sluggish OER process usually follows a four-step reaction mechanism. Consequently, further exploration of cost-effective water oxidation catalysts with promising activity and high stability are recognized to be primarily attractive and challenging.

In the past decades, the generations of two dimensional (2D) materials have aroused enormous interests in the field of electrocatalysis due to their distinguished structural and electronic characteristics. Whereas, investigations showed that the main drawback of 2D materials such as MoS2, WS2, and MoSe2 is their considerable low conductive capability. Recent advances indicate that black phosphorus (BP) is a metal-free layered semiconductor with relatively high carrier mobility. The unique layered structure in junction with promising electronic properties of BP, endow it to receive great attention in associate with superior electro-catalytic performances.

For instance, advance in electrocatalytic OER has been achieved by the group of Prof. Shuangyin Wang et al., where bulk BP demonstrated comparable electrocatalytic efficiency to that of commercial RuO2 catalysts. Although the results suggested that bulk BP is a promising electrocatalyst for OER, its bulk crystal structure still suffer from low active sites, which may become the main hurdle for achieving high efficient OER catalytic performances. Recent advances indicated that reducing the thickness or layer numbers of two-dimensional (2D) nanosheets would bring out additional exposed electrocatalytic active sites and increased surface area in comparison with their bulk counterparts. These beneficial characteristics can open up a new platform for using 2D layered materials to construct highly active electrocatalytic catalysts.

In a recent paper published in Advanced Energy Materials, researchers from Xiangtan University and Shenzhen University introduce an improved OER performance on 2D few-layer BP nanosheets which are obtained by liquid exfoliation. To conceive few-layer BP nanosheets as promising nanostructure for high efficient electrocatalysis, the electrocatalytic behavior of BP nanosheets have been investigated.

In detail, a comparative study has been performed to reveal the relation of current density between applied bias potential and concentration of OH, and the thickness-dependent electrochemical OER performances of BP nanosheets have been elucidated by adopting a selective centrifugation method. Compared to that of bulk BP, the electrochemical activity of BP nanosheets has been greatly improved. Electrochemical tests demonstrate the OER onset-potential and Tafel slope of BP nanosheets is 1.45 V and 88 mV/dec, respectively.

Additional thickness-dependent OER performances of BP nanosheets have been explored, where the OER activities of BP nanosheets showed improved tendency along with the reduction in thickness of BP nanosheets by means of centrifugation. The aims of the current research can provide fundamental information about the OER performance of BP nanosheets. It is, therefore, envisaged the present work can contribute to extendable investigations and applications towards high-performance BP-based OER electrocatalysts.

This study, Few-Layer Black Phosphorus Nanosheets as Electrocatalysts for Highly Efficient Oxygen Evolution Reaction, led by Prof. Han Zhang, Prof. Xiang Qi and his student Xiaohui Ren, provide comprehensive understanding on the electrochemical OER performance of BP nanosheets was recently published in the journal Advanced Energy Materials (DOI: 10.1002/aenm.201700396).

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