High-entropy alloys (HEAs) are promising candidates for the electrocatalyst of hydrogen evolution reaction (HER) due to their unique properties such as cocktail electronic effect and lattice distortion effect. Herein, the ultrasmall (sub-2 nm) nanoparticles of PtRuCoNiCu HEA with uniform element distribution are highly dispersed on hierarchical N-doped carbon nanocages (hNCNC) via low-temperature thermal reduction, denoted as us-HEA/hNCNC. The optimal us-HEA/hNCNC exhibits excellent HER performance in 0.5 M H₂SO₄ solution, achieving an ultralow overpotential of 19 mV at 10 mA·cm⁻² (without iR-compensation), high mass activity of 13.1 A·mg_{noble metals}⁻¹ at −0.10 V and superb stability with a slight overpotential increase of 3 mV after 20,000 cycles of cyclic voltammetry scans, much superior to the commercial Pt/C (20 wt.%). The combined experimental and theoretical studies reveal that the Pt&Ru serve as the main active sites for HER and the CoNiCu species modify the electron density of active sites to facilitate the H* adsorption and achieve an optimum M–H binding energy. The hierarchical pore structure and N-doping of hNCNC support also play a crucial role in the enhancement of HER activity and stability. This study demonstrates an effective strategy to greatly improve the HER performance of noble metals by developing the HEAs on the unique hNCNC support.

Semihydrogenation of trace acetylene in an ethylene gas stream is a vital step for the industrial production of polyethylene, in which Pd single-site catalysts (SSCs) have great potential. Herein, two Pd SSCs with different coordination structures are prepared on hierarchical nitrogen-doped carbon nanocages (hNCNC) by regulating the nitrogen species with or without using dicyandiamide. With using dicyandiamide, the obtained Pd₁-N_dicy/hNCNC SSC features the coordinated Pd by two pyridinic N and two pyrrolic N ( ${\text{PdN}}_{\text{2}}^{\text{py}}{\text{N}}_{\text{2}}^{\text{pr}}$). Without using dicyandiamide, the obtained Pd₁/hNCNC SSC features the coordinated Pd by pyridinic N and C ( ${\text{PdN}}_x^{\text{py}}{\text{C}}_{\text{4}-x}$, x = 1–4). The former exhibits an 18-fold increase in catalytic activity compared to the latter. Theoretical results reveal the abundant unoccupied orbital states above the Fermi level of ${\text{PdN}}_{\text{2}}^{\text{py}}{\text{N}}_{\text{2}}^{\text{pr}}$ moiety, which can facilitate the activation of substrate molecules and dynamics of acetylene hydrogenation as supported by the combined theoretical and experimental results. In addition, the ${\text{PdN}}_{\text{2}}^{\text{py}}{\text{N}}_{\text{2}}^{\text{pr}}$ moiety presents a favorable desorption of ethylene. Consequently, the Pd₁-N_dicy/hNCNC SSC exhibits high C₂H₂ conversion (99%) and C₂H₄ selectivity (87%) at 160 °C. This study demonstrates the impact of Pd single-site coordination structure on catalytic performance, which is significant for the rational design of advanced Pd SSCs on carbon-based supports.

Efficient, durable and economic electrocatalysts are crucial for commercializing water electrolysis technology. Herein, we report an advanced bifunctional electrocatalyst for alkaline water splitting by growing NiFe-layered double hydroxide (NiFe-LDH) nanosheet arrays on the conductive NiMo-based nanorods deposited on Ni foam to form a three-dimensional (3D) architecture, which exhibits exceptional performances for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In overall water splitting, only the low operation voltages of 1.45/1.61 V are required to reach the current density of 10/500 mA·cm⁻², and the continuous water splitting at an industrial-level current density of 500 mA·cm⁻² shows a negligible degradation (1.8%) of the cell voltage over 1000 h. The outstanding performance is ascribed to the synergism of the HER-active NiMo-based nanorods and the OER-active NiFe-LDH nanosheet arrays of the hybridized 3D architecture. Specifically, the dense NiFe-LDH nanosheet arrays enhance the local pH on cathode by retarding OH⁻ diffusion and enlarge the electrochemically active surface area on anode, while the conductive NiMo-based nanorods on Ni foam much decrease the charge-transfer resistances of both electrodes. This study provides an efficient strategy to explore advanced bifunctional electrocatalysts for overall water splitting by rationally hybridizing HER- and OER-active components.

Glycerol is an alternative sustainable fuel for fuel cells, and efficient electrocatalyst is crucial for glycerol oxidation reaction (GOR). The promising Pt catalysts are subject to the inadequate capability of C–C bond cleavage and the susceptibility to poisoning. Herein, Pt-Sn alloyed nanoparticles are immobilized on hierarchical nitrogen-doped carbon nanocages (hNCNCs) by convenient ethylene glycol reduction and subsequent thermal reduction. The optimal Pt₃Sn/hNCNC catalyst exhibits excellent GOR performance with a high mass activity (5.9 A·mg_Pt⁻¹), which is 2.7 and 5.4 times higher than that of Pt/hNCNC and commercial Pt/C, respectively. Such an enhancement can be mainly ascribed to the increased anti-poisoning and C–C bond cleavage capability due to the Pt₃Sn alloying effect and Sn-enriched surface, the high dispersion of Pt₃Sn active species due to N-participation, as well as the high accessibility of Pt₃Sn active species due to the three-dimensional (3D) hierarchical architecture of hNCNC. This study provides an effective GOR electrocatalyst and convenient approach for catalyst preparation.

The atomically dispersed Fe³⁺ sites of Fe-N-C single-site catalysts (SSCs) are demonstrated as the active sites for CO₂ electroreduction (CO₂RR) to CO but suffer from the reduction to Fe²⁺ at ~ −0.5 V, accompanied by the drop of CO faradaic efficiency (FE_CO) and deterioration of partial current (J_CO). Herein, we report the construction of F-doped Fe-N-C SSCs and the electron-withdrawing character of fluorine could stabilize Fe³⁺ sites, which promotes the FE_CO from the volcano-like highest value (88.2%@−0.40 V) to the high plateau (> 88.5%@−0.40–−0.60 V), with a much-increasedJ_CO (from 3.24 to 11.23 mA·cm⁻²). The enhancement is ascribed to the thermodynamically facilitated CO₂RR and suppressed competing hydrogen evolution reaction, as well as the kinetically increased electroactive surface area and improved charge transfer, due to the stabilized Fe³⁺ sites and enriched defects by fluorine doping. This finding provides an efficient strategy to enhance the CO₂RR performance of Fe-N-C SSCs by stabilizing Fe³⁺.

The cathode of lithium-oxygen (Li-O₂) batteries should have large space for high Li₂O₂ uptake and superior electrocatalytic activity to oxygen evolution/reduction for long lifespan. Herein, a high-performance MnO_x/hCNC cathode was constructed by the defect-induced deposition of manganese oxide (MnO_x) nanoparticles on hierarchical carbon nanocages (hCNC). The corresponding Li-O₂ battery (MnO_x/hCNC@Li-O₂) exhibited excellent electrocatalytic activity with the low overpotential of 0.73‒0.99 V in the current density range of 0.1‒1.0 A·g^–1. The full discharge capacity and cycling life of MnO_x/hCNC@Li-O₂ were increased by ~86.7% and ~91%, respectively, compared with the hCNC@Li-O₂ counterpart. The superior performance of MnO_x/hCNC cathode was ascribed to (i) the highly dispersed MnO_x nanoparticles for boosting the reversibility of oxygen evolution/reduction reactions, (ii) the interconnecting pore structure for increasing Li₂O₂ accommodation and facilitating charge/mass transfer, and (iii) the concealed surface defects of hCNC for suppressing side reactions. This study demonstrated an effective strategy to improve the performance of Li-O₂ batteries by constructing cathodes with highly dispersed catalytic sites and hierarchical porous structure.

The investigation of earth-abundant electrocatalysts for efficient water electrolysis is of central importance in renewable energy system, which is currently impeded by the large overpotential of oxygen evolution reaction (OER). NiFe sulfides show promising OER activity but are troubled by their low intrinsic conductivities. Herein, we demonstrate the construction of the porous core-shell heterojunctions of FeNi₃@(Fe, Ni)S₂ with tunable shell thickness via the reduction of hierarchical NiFe(OH)_x nanosheets followed by a partial sulfidization. The conductive FeNi₃ core provides the highway for electron transport, and the (Fe, Ni)S₂ shell offers the exposed surface for in situ generation of S-doped NiFe-oxyhydroxides with high intrinsic OER activity, which is supported by the combined experimental and theoretical studies. In addition, the porous hierarchical morphology favors the electrolyte access and O₂ liberation. Consequently, the optimized catalyst achieves an excellent OER performance with a low overpotential of 288 mV at 100 mA·cm^-2, a small Tafel slope of 48 mV·dec^-1, and a high OER durability for at least 1, 200 h at 200 mA·cm^-2. This study provides an effective way to explore the advanced earth-abundant OER electrocatalysts by constructing the heterojunctions between metal and corresponding metal-compounds via the convenient post treatment, such as nitridation and sulfidization.

Metal-nitrogen-carbon materials are promising catalysts for CO₂ electroreduction to CO. Herein, by taking the unique hierarchical carbon nanocages as the support, an advanced nickel-nitrogen-carbon single-site catalyst is conveniently prepared by pyrolyzing the mixture of NiCl₂ and phenanthroline, which exhibits a Faradaic efficiency plateau of > 87% in a wide potential window of -0.6 - -1.0 V. Further S-doping by adding KSCN into the precursor much enhances the CO specific current density by 68%, up to 37.5 A·g^-1 at -0.8 V, along with an improved CO Faradaic efficiency plateau of > 90%. Such an enhancement can be ascribed to the facilitated CO pathway and suppressed hydrogen evolution from thermodynamic viewpoint as well as the increased electroactive surface area and improved charge transfer fromkinetic viewpoint due to the S-doping. This study demonstrates a simple and effective approach to advanced electrocatalysts by synergetic modification of the porous carbon-based support and electronic structure of the active sites.

As a choke point in water electrolysis, the oxygen evolution reaction (OER) suffers from the severe electrode polarization and large overpotential. Herein, the porous hierarchical hetero-(Ni_3-xFe_x)FeN/Ni catalysts are in situ constructed for the efficient electrocatalytic OER. X-ray absorption fine structure characterizations reveal the strong Ni-Fe bimetallic interaction in (Ni_3-xFe_x)FeN/Ni. Theoretical study indicates the heterojunction and bimetallic interaction decrease the free-energy change for the rate-limiting step of the OER and the overpotential thereof. In addition, the high conductivity and porous hierarchical morphology favor the electron transfer, electrolyte access and O₂ release. Consequently, the optimized catalyst achieves a low overpotential of 223 mV at 10 mA·cm^-2, a small Tafel slope of 68 mV·dec^-1, and a high stability. The excellent performance of the optimized catalyst is also demonstrated by the overall water electrolysis with a low working voltage and high Faradaic efficiency. Moreover, the correlation between the structure and performance is well established by the experimental characterizations and theoretical calculations, which confirms the origin of the OER activity from the surface metal oxyhydroxide in situ generated upon applying the current. This study suggests a promising approach to the advanced OER electrocatalysts for practical applications by constructing the porous hierarchical metal-compound/metal heterojunctions.

Novel hierarchical carbon nanocages (hCNCs) are proposed as high-rate anodes for Li- and Na-ion batteries. The unique structure of the porous network for hCNCs greatly favors electrolyte penetration, ion diffusion, electron conduction, and structural stability, resulting in high rate capability and excellent cyclability. For lithium storage, the corresponding electrode stores a steady reversible capacity of 970 mAh·g^-1 at a rate of 0.1 A·g^-1 after 10 cycles, and stabilizes at 229 mAh·g^-1 after 10, 000 cycles at a high rate of 25 A·g^-1 (33 s for full-charging) while delivering a large specific power of 37 kW∙kg_electrode^–1 and specific energy of 339 Wh∙k_gelectrode^–1. For sodium storage, the hCNC reaches a high discharge capacity of ~50 mAh·g^-1 even at a high rate of 10 A·g^-1.