The coupling of photoanode (Pho) and oxygen evolution catalyst (OEC) is an ideal approach to enhance the photoelectrochemical (PEC) activity. Nevertheless, the anticipated photocurrent density has not been reached due to slow charge transfer dynamics and severe charge recombination at the interface. Herein, a novel “killing two birds with one stone” approach was discovered by employing CoPi as an interface mediator, which shifts its charge transfer behavior from conventional hole storage or passivation to hole transporter. The optimized BiVO₄/CoPi/FeOOH photoanode achieves a noteworthy photocurrent density of 5.4 mA/cm² and exhibits long term stability (13 h). The dynamic analysis and electrochemical characterization reveal that CoPi can rapidly and directly transfer more photogenerated holes to the surface of OEC in comparison to traditional slow holes transfer behavior, resulting in highly efficient interface charge separation. Interestingly, the strong interfacial interactions can also be extended to OEC/electrolyte interface, specifically by promoting the surface reaction dynamics. Moreover, this innovative approach of altering behavior of CoPi can also be utilized to design other photoanodes, like BiVO₄/CoPi/NiOOH, aimed at efficient PEC water splitting. This finding affords a smart strategy to develop highly efficient and stable photoelectrodes for water splitting.

Highly efficient metal-free, carbon-based, bi-functional electrocatalysts for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) have attracted increased attention for use in electrochemical energy conversion systems, owing to their low cost and high activity. In this work, N-doped carbon nanocages (N-CCs) with a porous self-supported architecture and high specific surface area are synthesized by a facile interfacial assembly synthetic route. The materials are comprehensively characterized by scanning electron microscopy, transmission electron microscopy, nitrogen adsorption–desorption experiments, X-ray diffraction, and X-ray photoelectron spectroscopy. Cyclic voltammetry, chronoamperometry, and linear sweep voltammetry demonstrate that the as-prepared N-CC could serve as an effective metal-free electrocatalyst with excellent catalytic activity, long-term operation durability, and excellent methanol tolerance for the ORR in alkaline media. In the presence of 3 mM methanol, the half wave potential of the N-CCs for the ORR is 190 mV; this is more positive than that of the commercial Pt/C electrocatalyst. Meanwhile, the N-CCs also show an OER activity comparable to that of the commercial Ru/C electrocatalyst, revealing their bifunctional property.

Catalysts for the oxygen reduction reaction (ORR) play an important role in fuel cells. Alternative non-precious metal catalysts with comparable ORR activity to Pt-based catalysts are highly desirable for the development of fuel cells. In this work, we report for the first time a spinel MnCo₂O₄/C ORR catalyst consisting of uniform MnCo₂O₄ nanoparticles cross-linked with two-dimensional (2D) porous carbon nanosheets (abbreviated as porous MnCo₂O₄/C nanosheets), in which glucose is used as the carbon source and NaCl as the template. The obtained porous MnCo₂O₄/C nanosheets present the combined properties of an interconnected porous architecture and a large surface area (175.3 m²·g^-1), as well as good electrical conductivity (1.15 × 10² S·cm^-1). Thus, the as-prepared MnCo₂O₄/C nanosheets efficiently facilitate electrolyte diffusion and offer an expedite transport path for reactants and electrons during the ORR. As a result, the as-prepared porous MnCo₂O₄/C nanosheet catalyst exhibits enhanced ORR activity with a higher onset potential and current density than those of its counterparts, including pure MnCo₂O₄, carbon nanosheets, and Vulcan XC-72R carbon. More importantly, the porous MnCo₂O₄/C nanosheets exhibit a comparable electrocatalytic activity but superior stability and tolerance toward methanol crossover effects than a high-performance Pt/C catalyst in alkaline medium. The synthetic strategy outlined here can be extended to other nonprecious metal catalysts for application in electrochemical energy conversion.