Carbon nanomaterials such as nanotubes, nanoflakes/nanowalls, and graphene have been used as electron sources due to their superior field electron emission (FEE) characteristics. However, these materials show poor stability and short lifetimes, which prevent their use in practical device applications. The aim of this study was to find an innovative nanomaterial possessing both high robustness and reliable FEE behavior. Herein, a hybrid structure of self-organized multi-layered graphene (MLG)–boron doped diamond (BDD) nanowall materials with superior FEE characteristics was successfully synthesized using a microwave plasma enhanced chemical vapor deposition process. Transmission electron microscopy reveals that the as-prepared carbon clusters have a uniform, dense, and sharp nanowall morphology with sp³ diamond cores encased by an sp² MLG shell. Detailed nanoscale investigations conducted using peak force-controlled tunneling atomic force microscopy show that each of the core–shell structured carbon cluster fields emits electrons equally well. The MLG–BDD nanowall materials show a low turn-on field of 2.4 V μm⁻¹, a high emission current density of 4.2 mA cm⁻² at an applied field of 4.0 V μm⁻¹, a large field enhancement factor of 4500, and prominently high lifetime stability (lasting for 700 min), which demonstrate the superiority of these materials over other hybrid nanostructured materials. The potential of these MLG-BDD hybrid nanowall materials in practical device applications was further illustrated by the plasma illumination behavior of a microplasma device with these materials as the cathode, where a low threshold voltage of 330 V (low threshold field of 330 V mm⁻¹) and long plasma stability of 358 min were demonstrated. The fabrication of these hybrid nanowalls is straight forward and thereby opens up a pathway for the advancement of next-generation cathode materials for high brightness electron emission and microplasma-based display devices.

Supercabatteries have the characteristics of supercapacitors and batteries, namely high power and energy densities as well as long cycle life. To construct them, capacitor electrodes with wide potential windows and/or redox electrolytes are required. Herein, graphite@diamond nano-needles and an aqueous solution of Fe(CN)₆ ^3−/4− are utilized as the capacitor electrode and the electrolyte, respectively. This diamond capacitor electrode has a nitrogen-doped diamond core and a nano-graphitic shell. In 0.05 M Fe(CN)₆ ^3−/4− + 1.0 M Na₂SO₄ aqueous solution, the fabricated supercabattery has a capacitance of 66.65 mF cm⁻² at a scan rate of 10 mV s⁻¹. It is stable over 10 000 charge/discharge cycles. The symmetric supercabattery device assembled using a two-electrode system possesses energy and power densities of 10.40 W h kg⁻¹ and 6.96 kW kg⁻¹, respectively. These values are comparable to those of other energy storage devices. Therefore, diamond supercabatteries are promising for many industrial applications.

Direct synthesis of a nano-structured carbon hybrid consisting of vertically aligned carbon nanograsses on top of boron-doped nanocrystalline diamond is demonstrated and the carbon hybrid is further applied as an electrode material for the fabrication of supercapacitors. The hybrid film combines the dual advantages of sp² (carbon nanograss) and sp³ (nanocrystalline diamond) bonded carbon, possessing not only the excellent electrical characteristics of sp² carbon but also the exceptional electrochemical stability of sp³ carbon. As a result, the specific capacitance of the as-prepared hybrid material reaches up to 0.4 F cm⁻², one of the highest reported in diamond-based supercapacitors. The entire electrochemical results exhibit enhanced electron transfer efficiency with remarkable stability of 95% of capacitance retention even after 10 000 cycles.

Heavy metal poisoning has a life-threatening impact on the human body to aquatic ecosystems. This necessitates designing a convenient green methodology for the fabrication of an electrochemical sensor that can detect heavy metal ions efficiently. In this study, boron (B) and nitrogen (N) co-doped laser-induced porous graphene (LIG_BN) nanostructured electrodes were fabricated using a direct laser writing technique. The fabricated electrodes were utilised for the individual and simultaneous electrochemical detection of lead (Pb²⁺) and cadmium (Cd²⁺) ions using a square wave voltammetry technique (SWV). The synergistic effect of B and N co-doping results in an improved sensing performance of the electrode with better sensitivity of 0.725 µA/µM for Pb²⁺ and 0.661 µA/µM for Cd²⁺ ions, respectively. Moreover, the sensing electrode shows a low limit of detection of 0.21 µM and 0.25 µM for Pb²⁺ and Cd²⁺ ions, with wide linear ranges from 8.0 to 80 µM for Pb²⁺ and Cd²⁺ ions and high linearity of R² = 0.99 in case of simultaneous detection. This rapid and facile method of fabricating heteroatom-doped porous graphene opens a new avenue in electrochemical sensing studies to detect various hazardous metal ions.

The improvement of the plasma illumination (PI) properties of a microplasma device due to the application of nanocrystalline diamond-decorated graphene nanoflakes (NCD-GNFs) as a cathode is investigated. The improved plasma illumination (PI) behavior is closely related to the enhanced field electron emission (FEE) properties of the NCD-GNFs. The NCD-GNFs possess better FEE characteristics with a low turn-on field of 9.36 V μm⁻¹ to induce the field emission, a high FEE current density of 2.57 mA cm⁻² and a large field enhancement factor of 2380. The plasma can be triggered at a low voltage of 380 V, attaining a large plasma current density of 3.8 mA cm⁻² at an applied voltage of 570 V. In addition, the NCD-GNF cathode shows enhanced lifetime stability of more than 21 min at an applied voltage of 430 V without showing any sign of degradation, whereas the bare GNFs can last only 4 min. The superior FEE and PI properties of the NCD-GNFs are ascribed to the unique combination of diamond and graphene. Transmission electron microscopic studies reveal that the NCD-GNFs contain nano-sized diamond films evenly decorated on the GNFs. Nanographitic phases in the grain boundaries of the diamond grains form electron transport networks that lead to improvement in the FEE characteristics of the NCD-GNFs.