Nitrogen-enriched polydopamine analogue-derived defect-rich porous carbon as a bifunctional metal-free electrocatalyst for highly efficient overall water splitting

The development of efficient, low-cost, and durable electrocatalysts toward both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) is of great significance for overall water splitting associated with renewable energy conversion and storage. Carbon-based nanomaterials have been widely employed as electrocatalysts for the independent HER or OER; however, research on bifunctional metal-free electrocatalysts for water splitting is still in its infancy and remains a formidable challenge to develop highly active catalysts for future applications. Here we report a highly active defect-rich, carbon-based, bifunctional metal-free water splitting electrocatalyst, prepared by a template approach, in which a nitrogen-enriched polydopamine analogue is used as the carbon precursor. The resultant defect-rich porous carbon (DRPC) exhibits a large specific surface area with a hierarchically micro/ mesoporous structure and a high nitrogen doping content with rich pyridinic N. Accordingly, the newly developed DRPC electrocatalysts display superb bifunctional catalytic activities for both the HER and the OER in alkaline solution, outperforming all other reported metal-free catalysts. Significantly, the DRPC catalyst couple-based alkaline water electrolyzer with strong durability delivers a 10 mA cm(-2) overall water splitting current at a considerably low voltage of 1.74 V, and a demonstration of a self-powered electrochemical water splitting system is also presented, highlighting its great potential for practical applications.