P-doped g-C3N4 has been successfully synthesized using hexachlorocyclotriphosphazene, a low cost and environmentally benign compound, as phosphorus source, and guanidiniumhydrochloride as g-C3N4 precursor, via a thermally induced copolymerization route.

Unraveling the descriptor of catalytic activity, which is related to physical properties of catalysts, is a major objective of catalysis research. In the present study, the first-principles calculations based on interfacial model were performed to study the oxygen evolution reaction mechanism of Li2O2 supported on active surfaces of transition-metal compounds (TMC: oxides, carbides, and nitrides). Our studies indicate that the O2 evolution and Li(+) desorption energies show linear and volcano relationships with surface acidity of catalysts, respectively. Therefore, the charging voltage and desorption energies of Li(+) and O2 over TMC could correlate with their corresponding surface acidity. It is found that certain materials with an appropriate surface acidity can achieve the high catalytic activity in reducing charging voltage and activation barrier of rate-determinant step. According to this correlation, CoO should have as active catalysis as Co3O4 in reducing charging overpotential, which is further confirmed by our comparative experimental studies. Co3O4, Mo2C, TiC, and TiN are predicted to have a relatively high catalytic activity, which is consistent with the previous experiments. The present study enables the rational design of catalysts with greater activity for charging reactions of Li-O2 battery.

A lithium-air battery as an energy storage technology can be used in electric vehicles due to its large energy density. However, its poor rate capability, low power density and large overpotential problems limit its practical usage. In this paper, the first-principles thermodynamic calculations were performed to study the catalytic activity of X-doped graphene (X = B, N, Al, Si, and P) materials as potential cathodes to enhance charge reactions in a lithium-air battery. Among these materials, P-doped graphene exhibits the highest catalytic activity in reducing the charge voltage by 0.25 V, while B-doped graphene has the highest catalytic activity in decreasing the oxygen evolution barrier by 0.12 eV. By combining these two catalytic effects, B,P-codoped graphene was demonstrated to have an enhanced catalytic activity in reducing the O2 evolution barrier by 0.70 eV and the charge voltage by 0.13 V. B-doped graphene interacts with Li2O2 by Li-sited adsorption in which the electron-withdrawing center can enhance charge transfer from Li2O2 to the substrate, facilitating reduction of O2 evolution barrier. In contrast, X-doped graphene (X = N, Al, Si, and P) prefers O-sited adsorption toward Li2O2, forming a X-O2(2-)···Li(+) interface structure between X-O2(2-) and the rich Li(+) layer. The active structure of X-O2(2-) can weaken the surrounding Li-O2 bonds and significantly reduce Li(+) desorption energy at the interface. Our investigation is helpful in developing a novel catalyst to enhance oxygen evolution reaction (OER) in Li-air batteries.

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Porous activated carbons (PACs) are promising candidates to capture CO through physical adsorption because of their chemical stability, easy-synthesis, cost-effectiveness and good recyclability. However, their low CO adsorption capacity, especially low CO/N selectivity, has limited their practical applications. In this work, an optimized PAC with a large specific surface area, a small micropore size, and a large micropore volume has been synthesized by one-step carbonization/activation of casein using KCO as a mild activation agent. It showed a remarkably enhanced CO adsorption capacity as high as 5.78 mmol g and an excellent CO/N selectivity of 144 (25 °C, 1 bar). Based on DFT calculations and experimental results, the coexistence of adjacent pyridinic N and -OH/-NH species was proposed for the first time to make an important contribution to the ultra-high CO adsorption performance, especially CO/N selectivity. This work provides effective guidance to design PAC adsorbents with high CO adsorption performance. The content of pyridine N combined with -OH/-NH was further elevated by additional nitrogen introduction, resulting in a further enhanced CO adsorption capacity up to 5.96 mmol g (25 °C, 1 bar). All these results suggest that, in addition to the well-defined pore structure, pyridinic N with neighboring OH or NH species played an important role in enhancing the CO adsorption performance of PACs, thus providing effective guidance for the rational design of CO adsorbents.

Tunable H2O–F− hydrogen bonding is crucial to the structural stability and electrochemical performance of FeF3·0.33H2O cathode materials.

Tuning the composition of discharge products is an important strategy to reduce charge potential, suppress side reactions, and improve the reversibility of metal-oxygen batteries. In the present study, first-principles calculations and experimental confirmation were performed to unravel the influence of O pressure, particle size, and electrolyte on the composition of charge products in Na-O batteries. The electrolytes with medium and high donor numbers (>12.5) are favorable for the formation of sole NaO, while those with low donor numbers (<12.5) may permit the formation of NaO by disproportionation reactions. Our comparative experiments under different electrolytes confirmed the calculation prediction. Our calculations indicated that O pressure and particle size hardly affect discharge products. On the electrode, only one-electron-transfer electrochemical reaction to form NaO takes place, whereas two-electron-transfer electrochemical and chemical reactions to form NaO and NaO are prevented in thermodynamics. The present study explains why metastable NaO was identified as a sole discharge product in many experiments, while thermodynamically more stable NaO was not observed. Therefore, to achieve low overpotential, a high-donor-number electrolyte should be applied in the discharge processes of Na-O batteries.

Rechargeable lithium-O 2 battery is considered as promising next-generation devices for energy storage and conversion because of their high theoretical specific energy density. However, its application suffers from several issues such as high overpotential, poor cycle performance, and limited rate capability. Tuning electrochemical/chemical reactions in discharge and charge play an important role in reducing overpotential, increasing current density, and improving reversibility of Li-O 2 batteries. In this review, the fundamental principles and complicated electrochemical and chemical reactions in electrolytes and cathodes are first discussed. Based on these mechanisms, various strategies such as stabilizing electrode materials, selecting suitable electrolytes, adding catalysts and mediators, and changing O 2 pressure are reviewed to improve electrochemical performance by tuning electrochemical/chemical reactions. Finally, we explore future research directions in improving electrochemical performance of lithium-O 2 battery.