Zn-air batteries (ZABs) as a potential energy conversion system suffer from low power density (typically ≤ 200 mW·cm⁻²). Recently, three-dimensional (3D) integrated air cathodes have demonstrated promising performance over traditional two-dimensional (2D) plane ones, which is ascribed to enriched active sites and enhanced diffusion, but without experimental evidence. Herein, we applied a bubble pump consumption chronoamperometry (BPCC) method to quantitatively identify the gas diffusion coefficient (D) and effective catalytic sites density (ρ_EC) of the integrated air cathodes for ZABs. Furthermore, the D and ρ_EC values can instruct consequent optimization on the growth of Co embedded N-doped carbon nanotubes (CoNCNTs) on carbon fiber paper (CFP) and aerophilicity tuning, giving 4 times D and 1.3 times ρ_EC over the conventional 2D Pt/C-CFP counterparts. As a result, using the CoNCNTs with half-wave potential of merely 0.78 V vs. RHE (Pt/C: 0.89 V vs. RHE), the superaerophilic CoNCNTs-CFP cathode-based ZABs exhibited a superior peak power density of 245 mW·cm⁻² over traditional 2D Pt/C-CFP counterparts, breaking the threshold of 200 mW·cm⁻². This work reveals the intrinsic feature of the 3D integrated air cathodes by yielding exact D and ρ_EC values, and demonstrates the feasibility of BPCC method for the optimization of integrated electrodes, bypassing trial-and-error strategy.

Pt-based catalysts are used commercially for the hydrogen evolution reaction (HER), even though the low earth abundance and high cost of platinum hinder scale-up applications. Ru metal is a promising alternative catalyst for HER owing to its lower cost but similar metal–hydrogen bond strength to Pt. However, designing an efficient and robust Ru-based electrocatalyst for pH-universal HER is challenging. Herein, we successfully synthesized N-doped carbon (NC) supported ruthenium catalysts with different Ru sizes (single-atoms, nanoclusters and nanoparticles), and then systematically evaluated their performance for HER. Among these catalysts, the Ru nanocluster catalyst (Ru NCs/NC) displayed optimal catalytic performance with overpotentials of only 14, 30, and 32 mV (at 10 mA·cm⁻²) in 1 M KOH, 1 M phosphate buffer saline (PBS), and 0.5 M H₂SO₄, respectively. The corresponding mass activities were 32.2, 12.1 and 8.1 times higher than those of 20 wt.% Pt/C, and also much better than those of the Ru single-atoms (Ru SAs/NC) and Ru nanoparticle (Ru NPs/NC) catalysts, at an overpotential of 100 mV under alkaline, neutral and acidic conditions, respectively. Density functional theory (DFT) calculations revealed that the outstanding HER performance of the Ru NCs/NC catalyst resulted from a strong interaction between the Ru nanoclusters and the N-doped carbon support, which downshifted the d-band center and thus weakened the *H adsorption ability of Ru sites.

Fe-N-C materials with atomically dispersed Fe–N₄ sites could tolerate the poisoning of phosphate, and is regarded as the most promising alternative to costly Pt-based catalysts for the oxygen reduction in high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs). However, they still face the critical issue of insufficient activity in phosphoric acid. Herein, we demonstrate a P-doping strategy to increase the activity of Fe-N-C catalyst via a feasible one-pot method. X-ray absorption spectroscopy and electron microscopy with atomic resolution indicated that the P atom is bonded with the N in Fe–N₄ site through C atoms. The as prepared Fe-NCP catalyst shows a half-wave potential of 0.75 V (vs. reversible hydrogen electrode (RHE), 0.1 M H₃PO₄), which is 60 and 40 mV higher than that of Fe-NC and commercial Pt/C catalysts, respectively. More importantly, the Fe-NCP catalyst could deliver a peak power density of 357 mW·cm⁻² in a high temperature fuel cell (160 °C), exceeding the non-noble-metal catalysts ever reported. The enhancement of activity is attributed to the increasing charge density and poisoning tolerance of Fe–N₄ caused by neighboring P. This work not only promotes the practical application of Fe-N-C materials in HT-PEMFCs, but also provides a feasible P-doping method for regulating the structure of single atom site.

Rechargeable aqueous zinc ion batteries (AZIBs) based on manganese dioxide (MnO₂) have received much attention for large-scale energy storage applications, however, their energy density is mainly limited by the one-electron reaction of Mn⁴⁺/Mn³⁺ redox. Herein, Mo doped δ-MnO₂ (Mo-MnO₂) is prepared and used as a high-performance cathode for AZIBs, which delivers an ultrahigh specific capacity of 652 mAh·g⁻¹ at 0.2 A·g⁻¹ based on the two-step two-electron redox reaction of Mn⁴⁺ $\rightleftharpoons$ Mn³⁺ $\rightleftharpoons$ Mn²⁺. Ex-situ structural analysis and density functional theory calculation reveal that the Mo⁵⁺ dopant plays an important role in enhancing the electronic conductivity of Mo-MnO₂ and promoting Jahn–Teller distortion of octahedral [MnO₆] in ZnMn₂O₄, which facilitates the second step redox reaction of Mn³⁺/Mn²⁺. This work provides a novel cathode materials design with multi-electron redox chemistry to achieve high energy density in AZIBs.

Active and durable electrocatalysts for methanol oxidation reaction are of critical importance to the commercial viability of direct methanol fuel cell, which has already attracted growing popularities. However, current methanol oxidation electrocatalysts fall far short of expectations and suffer from excessive use of noble metal, mediocre activity, and rapid decay. Here we report the Pt anchored on NiFe-LDHs surface hybrid for stable methanol oxidation in alkaline media. Based on the high intrinsic methanol oxidation activity of Pt nanoparticles, the substrates NiFe-LDHs further enhanced anti-poisoning ability and maintained unaffected stability after 200,000 s cycle test compared to commercial Pt/C catalyst. The use of NiFe-LDHs is believed to play the decisive role to evenly disperse Pt nanoparticles on their surface using single atomic dispersed Fe as anchoring sites, making full use of abundant OH groups and subsequent facilitating the oxidative removal of carbonaceous poison on neighboring Pt sites. This work highlights the specialty of NiFe-LDHs in improving the overall efficiency of methanol oxidation reaction.

Porous monolithic catalysts with high specific surface areas, which can not only facilitate heat/mass transfer, but also help to expose active sites, are highly desired in strongly exothermic or endothermic gas–solid phase reactions. In this work, hierarchical spinel monolithic catalysts with a porous woodpile architecture were fabricated via extrusion-based three-dimensional (3D) printing (direct ink writing, DIW in brief) of aluminate-intercalated layered double hydroxide (AI-LDH) followed by low temperature calcination. The intercalation of aluminate in LDH is found crucial to tailor the M²⁺/Al³⁺ ratio, integrate LDH nanosheets into monolithic catalyst, and enable the conversion of LDH to spinel at the temperature as low as 500 °C with high specific surface areas (> 350 m²/g). The rapid mass/heat transfer resulted from the versatile 3D network at macroscale and the highly dispersed and fully exposed active sites benefited from the porous structure at microscale endow the 3D-printed Pd loaded spinel MgAl-mixed metal oxide (3D-AI-Pd/MMO) catalyst with excellent catalytic performance in semi-hydrogenation of acetylene, achieving 100% conversion at 60 °C with more than 84% ethylene selectivity.

Single-atom metal-incorporated carbon nanomaterials (CMs) have shown great potential towards broad catalytic applications. In this work, we show that N-doped porous CMs embedded with redox-able Zn atoms exhibit superior capacitive performance. High Zn (~ 2.72 at.%)/N (~ 12.51 at.%) doping were realized by incorporating Zn²⁺ and benzamide into the condensation and carbonization of formamide and subsequent annealing at 900 °C. The Zn and N species are mutually benefited during the formation of ZnN₄ motif. The as-obtained Zn₁NC material affords a very large capacitance of 621 F·g⁻¹ (at 0.1 A·g⁻¹), superior rate capability (~ 65% retention at 100 A·g⁻¹), and excellent cycling stability (0.00044% per cycle at 10 A·g⁻¹). These merits are attributed to the high Zn/N loading, atomic Zn-boosted pseudocapacitive behavior, large specific surface area (~ 1,085 m²·g⁻¹), and rich pore hierarchy, thus ensuring both large pseudo-capacitance (e.g., ~ 37.9% at 10 mV·s⁻¹) and double-layer capacitance. Besides of establishing a new type of high Zn/N-loading carbon materials, our work uncovers the capacitive roles of atomically dispersed metals in CMs.

Understanding bubbles evolution kinetics on electrodes with varied geometries is of fundamental importance for advanced electrodes design in gas evolution reaction. In this work, the evolution kinetics of electro-generated hydrogen bubbles are recorded in situ on three (i.e. smooth, nanoporous, and nanoarray) Pt electrodes to identify the geometry dependence. The bubble radius shows a time-dependent growth kinetic, which is tightly-connected to the electrode geometry. Among the three electrodes, the smooth one shows a typical time coefficient of 0.5, in consistence with reported values; the nanoporous one shows a time coefficient of 0.47, less than the classic one (0.5); while the nanoarray one exhibits fastest bubble growth kinetics with a time coefficient higher than 0.5 (0.54). Moreover, the nanoarray electrode has the smallest bubble detachment size and the largest growth coefficient (23.3) of all three electrodes. Based on the experimental results, a growth model combined direct bottom- injection with micro-convection is proposed to illustrate the surface geometry dependent coefficients, i.e., the relationship between geometry and bubble evolution kinetics. The direct injection of generated gas molecules from the bottom of bubbles at the three phase boundaries are believed the key to tailor the bubble wetting states and thus determine the bubble evolution kinetics.

Oxygen evolution reaction is critical for water splitting or metal-air batteries, but previous research mainly focuses on electrode material or structure optimization. Herein, we demonstrate that surfactant modification of a NiFe layered double hydroxide (LDH) array electrode, one of the best catalysts for oxygen evolution reaction (OER), could achieve superaerophobic surface with balanced surface charges, affording fast mass transfer, quick gas release, and boosted OER performance. The assembled surfactants on the electrode surface are responsible for lowering the bubble adhesive force (~ 1.03 μN) and corresponding fast release of small bubbles generated during OER. In addition, the bipolar nature of the hexadecyl trimethyl ammonium bromide (CTAB) molecule lead to bilayer assembly of the surfactants with the polar ends facing the electrode surface and the electrolyte, resulting in neutralized charges on the electrode surface. As a result, OH^- transfer was facilitated and OER performance was enhanced. With the modified superaerophobic surface and balanced surface charge, NiFe LDHs-CTAB nanostructured electrode showed ultrahigh current density increase (9.39 mA/(mV cm²)), 2.3 times higher than that for conventional NiFe LDH nanoarray electrode), dramatically fast gas release, and excellent durability. The introduction of surfactants to construct under-water superaerophobic electrode with in-time repelling ability to the as-formed gas bubbles may open up a new pathway for designing efficient electrodes for gas evolution systems with potentially practical application in the near future.