The cathodic oxygen reduction reaction (ORR) is essential in the electrochemical energy conversion of fuel cells. Here, through the NH₃ atmosphere annealing of a graphene oxide (GO) precursor containing trace amounts of Ru, we have synthesized atomically dispersed Ru on nitrogen-doped graphene that performs as an electrocatalyst for the ORR in acidic medium. The Ru/nitrogen-doped GO catalyst exhibits excellent four-electron ORR activity, offering onset and half-wave potentials of 0.89 and 0.75 V, respectively, vs a reversible hydrogen electrode (RHE) in 0.1 M HClO₄, together with better durability and tolerance toward methanol and carbon monoxide poisoning than seen in commercial Pt/C catalysts. X-ray adsorption fine structure analysis and aberration-corrected high-angle annular dark-field scanning transmission electron microscopy are performed and indicate that the chemical structure of Ru is predominantly composed of isolated Ru atoms coordinated with nitrogen atoms on the graphene substrate. Furthermore, a density function theory study of the ORR mechanism suggests that a Ru-oxo-N₄ structure appears to be responsible for the ORR catalytic activity in the acidic medium. These findings provide a route for the design of efficient ORR single-atom catalysts.

An automated metal powder three-dimensional (3D) printing method for in situ synthesis of free-standing 3D graphene foams (GFs) was successfully modeled by manually placing a mixture of Ni and sucrose onto a platform and then using a commercial CO₂ laser to convert the Ni/sucrose mixture into 3D GFs. The sucrose acted as the solid carbon source for graphene, and the sintered Ni metal acted as the catalyst and template for graphene growth. This simple and efficient method combines powder metallurgy templating with 3D printing techniques and enables direct in situ 3D printing of GFs with no high-temperature furnace or lengthy growth process required. The 3D printed GFs show high-porosity (∼99.3%), low-density (∼0.015g cm^–3), high-quality, and multilayered graphene features. The GFs have an electrical conductivity of ∼8.7 S cm^–1, a remarkable storage modulus of ∼11 kPa, and a high damping capacity of ∼0.06. These excellent physical properties of 3D printed GFs indicate potential applications in fields requiring rapid design and manufacturing of 3D carbon materials, for example, energy storage devices, damping materials, and sound absorption.

Zn-ion hybrid supercapacitors (ZHSs) are an advanced energy storage system with high energy/power density. However, the development of cathodes with high-performance is still a challenge. Herein, N, O co-doped hierarchical porous carbon (HPC) integrated with carbon cloth (CC) was fabricated as a promising cathode for aqueous ZHSs, which delivered a high specific capacity of 138.5 mA h g⁻¹ with excellent rate performance ( 75 mA h g⁻¹ at 20 A g⁻¹) and superb cycling stability without decay after 10 000 cycles. As a result, an exceptionally high energy density of 110 W h kg⁻¹ and attractive power density of 20 kW kg⁻¹ can be obtained. More importantly, the dual cation (H⁺ and Zn²⁺) chemical absorption process for additional capacity is firstly proposed and verified by ex situ experiments, while the precipitation/dissolution process of zinc hydroxide sulphate hydrate is explained. Furthermore, a quasi-solid-state HPC/CC-based ZHS device based on gel electrolyte also showed promising potential for practical applications. This work provides a new pathway to develop carbon-based cathode materials for sustainable ZHSs.

The drive for significant advancement in battery capacity and energy density inspired a revisit to the use of Li metal anodes. We report the use of a seamless graphene–carbon nanotube (GCNT) electrode to reversibly store Li metal with complete dendrite formation suppression. The GCNT-Li capacity of 3351 mAh g^–1_GCNT-Li approaches that of bare Li metal (3861 mAh g^–1_Li), indicating the low contributing mass of GCNT, while yielding a practical areal capacity up to 4 mAh cm^–2 and cycle stability. A full battery based on GCNT-Li/sulfurized carbon (SC) is demonstrated with high energy density (752 Wh kg^–1 total electrodes, where total electrodes = GCNT-Li + SC + binder), high areal capacity (2 mAh cm^–2), and cyclability (80% retention at >500 cycles) and is free of Li polysulfides and dendrites that would cause severe capacity fade.

Electrically splitting water to H₂ and O₂ is a preferred method for energy storage as long as no CO₂ is emitted during the supplied electrical input. Here we report a laser-induced graphene (LIG) process to fabricate efficient catalytic electrodes on opposing faces of a plastic sheet, for the generation of both H₂ and O₂. The high porosity and electrical conductivity of LIG facilitates the efficient contact and charge transfer with the requisite electrolyte. The LIG-based electrodes exhibit high performance for hydrogen evolution reaction and oxygen evolution reaction with excellent long-term stability. The overpotential reaches 100 mA/cm² for HER, and OER is as low as 214 and 380 mV with relatively low Tafel slopes of 54 and 49 mV/dec, respectively. By serial connecting of the electrodes with a power source in an O-ring setup, H₂ and O₂ are simultaneously generated on either side of the plastic sheet at a current density of 10 mA/cm² at 1.66 V and can thereby be selectively captured. The demonstration provides a promising route to simple, efficient, and complete water splitting.