Kaicai Fan

The escalating demand for ammonia (NH₃) as a promising energy vector and essential chemical raw material in both industrial and agricultural applications, coupled with its noxious and caustic properties, has led to significant atmospheric emissions that pose environmental and health risks. Photocatalytic NH₃ oxidation over TiO₂ is a promising strategy for air purification but is hindered by poor selectivity, often leading to the formation of toxic NO_x byproducts due to the complex reaction network involving multiple competing pathways and intermediates. This study addresses this selectivity issue by designing a modified TiO₂ photocatalyst through a synergistic defect-dopant engineering approach. Through controlled doping and defect engineering, we demonstrate that N doping and O_Vs distinctly modulate the reaction mechanism and products' selectivity. Nitrogen doping thermodynamically promotes N₂ formation by stabilizing NH₂ intermediates and facilitating their selective coupling with NO, whereas O_Vs kinetically facilitate NH₃ and O₂ dissociation, promoting superoxide-mediated oxidation, leading to overoxidized products such as NO_x and nitrate/nitrite HNO_x^- species. An optimal N-doped TiO₂ catalyst achieves 87% NH₃ conversion with 80% N₂ selectivity and minimal NO_x emission (∼5 ppm), while exhibiting excellent stability over multiple cycles. This work elucidates a defect-dopant strategy that optimizes kinetic and thermodynamic aspects of NH₃ oxidation, providing a design principle for selective photocatalytic nitrogen management toward sustainable air purification.

Efficient and durable oxygen evolution reaction (OER) catalysts are crucial for the generation of hydrogen via alkaline seawater electrolysis. Herein, an FeOOH/NiFe-LDH heterostructure with a built-in electric field (BEF) has been synthesized on Ni foam through a one-step cathodic electrodeposition. The formed BEF accelerates the OER kinetics by optimizing the interfacial electronic structure and enhancing the mass transfer and stabilizes the structure of the catalyst by Fe-O-Ni-O-Fe coupling bonds. In addition, the BEF and FeOOH mutually reduce the adsorption of Cl^- on the catalyst. Accordingly, FeOOH/NiFe-LDH demonstrates an outstanding OER catalytic performance in alkaline seawater electrolytes. In detail, FeOOH/NiFe-LDH displays small η₁₀₀ values of 265 and 278 mV in alkaline simulated and natural seawater, respectively, and achieves exceptional durability with smooth operation for ∼150 h at 250 mA cm^-2, albeit in a high-salt electrolyte (1 M KOH and 2.5 M NaCl). When FeOOH/NiFe-LDH is used as the anode of the AEM electrolyzer, the cell in alkaline simulated seawater delivers low voltages of 1.59 and 1.92 V at 100 and 500 mA cm^-2, respectively. The cell also shows excellent durability after operation over 110 h at 250 mA cm^-2 with an insignificant voltage increase of only 27 mV (∼0.25 mV h^-1). This work provides insight into the catalytic mechanism of the BEF-based heterostructure as anodic catalysts for alkaline seawater electrolysis.

The chlor-alkali process plays an irreplaceable role in global chemical industry, but relies heavily on RuO₂ (or IrO₂)/TiO₂-based dimensionally stable anodes, hindering sustainability and new applications. We report a facile oxygenation activation approach to create apt oxygen groups on commercial carbon black and carbon cloth. Our experimental and theoretical studies reveal that creation of carbonyl, cyclic ether, and carboxyl groups on the graphitic plane edges gives commercial carbon materials superb chlorine evolution reaction activity (overpotential: 204 mV at 1 A cm^-2), selectivity (average Faraday efficiency: 99.6 ± 1.3%), and stability (stable operation for 100 h at 0.5 A cm^-2), which is comparable to or better than the benchmark RuO₂ and dimensionally stable anodes.

The rational design of efficient oxygen reduction reaction (ORR) catalysts with maximized atom utilization is essential for advancing the oxygen depolarized cathode technology. Here, we report atomically dispersed Fe, P heteronuclear catalytic pairs on hierarchical porous carbon, in which the hydrogen bond between Fe, P catalytic pairs and ORR intermediates significantly enhances the adsorption/desorption kinetics and lowers the rate-determining step barrier of OH* desorption. Thus, Fe,P/HPC delivers an alkaline ORR performance with a half-wave potential (E_1/2) of 0.92 V and retains ∼90% of the initial activity even after 150 h operation. In addition, Fe,P/HPC achieves an E_1/2 of 0.74 V in 0.1 M HClO₄. The Fe,P/HPC-based aqueous Zn-air battery (A-ZAB) achieves a high power density of 262 mW cm^-2 and exhibits enhanced stability, sustaining a minimal voltage gap over 2800 h of constant-current cycling. Moreover, the quasi-solid-state Zn-air battery (QSS-ZAB) delivers a large open-circuit voltage of 1.52 V, while maintaining a cycling stability for over 95 h at 0.5, 1, and 2 mA cm^-2, respectively. In the chlor-alkali process, the Fe,P/HPC||RuO₂ electrolyzer enables a large current density of 300 mA cm^-2 at 1.66 V and maintains stability over 110 h. The present work pioneers the designing and construction of atomic-level heteronuclear catalysts for practical and durable cathode.

Transition‐metal‐based compounds have been intensively explored as efficient electrocatalysts for hydrogen evolution reaction (HER). Feasible reconstruction to the real active sites, which is yet to be identified, endows the promotion of HER activity. Here, it is reported that the incoming S coordinates and anion vacancies prompt the structural reconstruction of S‐doped Co₃O₄ on carbon cloth (S‐Co₃O₄/CC) during HER. A list of in situ studies reveals that the real active sites for HER are the “metallic surface‐adparticles” system embracing metallic Co scaffold and the dilute coverage of S coordinated Co^δ+. Reaction mechanism exploration illustrates that interfacial perimeters between the coverage of Co₃S₄ moieties and metallic Co considerably facilitate the adsorption of H*, improve the kinetics of water dissociation, and consequently promote HER activity. The exemplified sulfide‐mediated topotactic transformation strategy is extended to the preparation of S, Fe codoped Ni(OH)₂ (S‐NiFe/CC) as a bifunctional electrocatalyst. The assembled anion exchange membrane water electrolyzer achieves a current density of 1.0 A cm⁻² at 1.72 V, showing excellent capability in catalyzing overall water splitting at ampere level. This study, showing a feasible strategy that enables the facile reconstruction to identify active sites, would inspire the development of efficient electrocatalysts for HER and other electrochemical hydrogenation reaction.

Controlled functionalization of 2D black phosphorus (BP) nanosheets provides unique opportunities to tune their chemical, physical, and electronic properties. Herein, the preparation of single‐atom nickel‐doped BP (Ni–BP) sheets using a simple solution‐based strategy is reported. Using the Ni–BP sheets as a passivation layer on top of a perovskite film leads to standard perovskite solar cells (PSCs) with improved performance. The standard n–i–p PSCs with the Ni–BP interlayer achieve maximum power conversion efficiencies of over 22%, with negligible hysteresis and a modest improvement in stability when subjected to different testing conditions. The perovskite films prepared with Ni–BP sheets‐based passivation are found to have reduced defect densities as well as improved charge‐transfer properties and carrier lifetimes. Density‐functional theory calculations support the experimental results through showing that the atomic Ni‐doping increases the work function of the BP interlayer, enabling better hole extraction, as well as increasing the surface hydrophobicity of the BP layer, hence reducing water sorption into the perovskite film.