Graphene‐Like Carbon Nitride Nanosheets for Improved Photocatalytic Activities

“Graphitic” (g)‐C₃N₄ with a layered structure has the potential of forming graphene‐like nanosheets with unusual physicochemical properties due to weak van der Waals forces between layers. Herein is shown that g‐C₃N₄ nanosheets with a thickness of around 2 nm can be easily obtained by a simple top‐down strategy, namely, thermal oxidation etching of bulk g‐C₃N₄ in air. Compared to the bulk g‐C₃N₄, the highly anisotropic 2D‐nanosheets possess a high specific surface area of 306 m² g^?1, a larger bandgap (by 0.2 eV), improved electron transport ability along the in‐plane direction, and increased lifetime of photoexcited charge carriers because of the quantum confinement effect. As a consequence, the photocatalytic activities of g‐C₃N₄ nanosheets have been remarkably improved in terms of ?OH radical generation and photocatalytic hydrogen evolution.     

Effective Prevention of Charge Trapping in Graphitic Carbon Nitride with Nanosized Red Phosphorus Modification for Superior Photo(electro)catalysis

The high occurrence of trapped unreactive charges due to chemical defects seriously affects the performance of g‐C₃N₄ in photocatalytic applications. This problem can be overcome by introducing ultrasmall red phosphorus (red P) crystals on g‐C₃N₄ sheets. The elemental red P atoms reduce the number of defects in the g‐C₃N₄ structure by forming new chemical bonds for much more effective charge separation. The product shows significantly enhanced photocatalytic activity toward hydrogen production. To the best of our knowledge, the hydrogen evolution rate obtained on this hybrid should be the highest among all P‐containing g‐C₃N₄ photocatalysts reported so far. The trapping and detrapping processes in this red P/g‐C₃N₄ system are thoroughly revealed by using time‐resolved transient absorption spectroscopy.     

Ice‐Assisted Synthesis of Black Phosphorus Nanosheets as a Metal‐Free Photocatalyst: 2D/2D Heterostructure for Broadband H2 Evolution

A 2D/2D heterojunction of black phosphorous (BP)/graphitic carbon nitride (g‐C₃N₄) is designed and synthesized for photocatalytic H₂ evolution. The ice‐assisted exfoliation method developed herein for preparing BP nanosheets from bulk BP, leads to high yield of few‐layer BP nanosheets (≈6 layers on average) with large lateral size at reduced duration and power for liquid exfoliation. The combination of BP with g‐C₃N₄ protects BP from oxidation and contributes to enhanced activity both under λ > 420 nm and λ > 475 nm light irradiation and to long‐term stability. The H₂ production rate of BP/g‐C₃N₄ (384.17 µmol g^?1 h^?1) is comparable to, and even surpasses that of the previously reported, precious metal‐loaded photocatalyst under λ > 420 nm light. The efficient charge transfer between BP and g‐C₃N₄ (likely due to formed N? P bonds) and broadened photon absorption (supported both experimentally and theoretically) contribute to the excellent photocatalytic performance. The possible mechanisms of H₂ evolution under various forms of light irradiation is unveiled. This work presents a novel, facile method to prepare 2D nanomaterials and provides a successful paradigm for the design of metal‐free photocatalysts with improved charge‐carrier dynamics for renewable energy conversion.     

Engineering the Photocatalytic Behaviors of g/C3N4‐Based Metal‐Free Materials for Degradation of a Representative Antibiotic

Graphitic carbon nitride (g/C₃N₄) is of promise as a highly efficient metal‐free photocatalyst, yet engineering the photocatalytic behaviours for efficiently and selectively degrading complicated molecules is still challenging. Herein, the photocatalytic behaviors of g/C₃N₄ are modified by tuning the energy band, optimizing the charge extraction, and decorating the cocatalyst. The combination shows a synergistic effect for boosting the photocatalytic degradation of a representative antibiotic, lincomycin, both in the degradation rate and the degree of decomposition. In comparison with the intrinsic g/C₃N₄, the structurally optimized photocatalyst shows a tenfold enhancement in degradation rate. Interestingly, various methods and experiments demonstrate the specific catalytic mechanisms for the multiple systems of g/C₃N₄‐based photocatalysts. In the degradation, the active species, including ·O₂^?, ·OH, and h⁺, have different contributions in the different photocatalysts. The intermediate, H₂O₂, plays an important role in the photocatalytic process, and the detailed functions and originations are clarified for the first time.     

Freestanding Graphitic Carbon Nitride Photonic Crystals for Enhanced Photocatalysis

Graphitic carbon nitride (g‐C₃N₄) has attracted tremendous attention in photocatalysis due to its extraordinary features, such as good thermal and chemical stability, metal‐free composition, and easy preparation. However, the photocatalytic performance of g‐C₃N₄ is still restricted by the limited surface area, inefficient visible light absorption, and high recombination rate of photoinduced charge carriers. Herein, a facile synthesis to produce freestanding g‐C₃N₄ photonic crystals (PCs) by crack‐free, highly ordered colloid crystals templating is reported. The PC structure succeeded from the silica opals induces bicontinuous framework, stronger optical absorption, and increase in the lifetime of photoexcited charge carriers compared to that of the bulk g‐C₃N₄, while the chemical structure remains similar to that of the bulk g‐C₃N₄. As such, the g‐C₃N₄ PCs have a much higher photodegradation kinetic of methyl orange and photocatalytic hydrogen production rate which is nearly nine times the rate of bulk g‐C₃N₄.     

Unique PCoN Surface Bonding States Constructed on g‐C3N4 Nanosheets for Drastically Enhanced Photocatalytic Activity of H2 Evolution

Developing high‐efficiency and low‐cost photocatalysts by avoiding expensive noble metals, yet remarkably improving H₂ evolution performance, is a great challenge. Noble‐metal‐free catalysts containing Co(Fe)?N?C moieties have been widely reported in recent years for electrochemical oxygen reduction reaction and have also gained noticeable interest for organic transformation. However, to date, no prior studies are available in the literature about the activity of N‐coordinated metal centers for photocatalytic H₂ evolution. Herein, a new photocatalyst containing g‐C₃N₄ decorated with CoP nanodots constructed from low‐cost precursors is reported. It is for the first time revealed that the unique P(δ^?)?Co(δ⁺)?N(δ^?) surface bonding states lead to much superior H₂ evolution activity (96.2 µmol h^?1) compared to noble metal (Pt)‐decorated g‐C₃N₄ photocatalyst (32.3 µmol h^?1). The quantum efficiency of 12.4% at 420 nm is also much higher than the record values (≈2%) of other transition metal cocatalysts‐loaded g‐C₃N₄. It is believed that this work marks an important step toward developing high‐performance and low‐cost photocatalytic materials for H₂ evolution.     

In Situ Bond Modulation of Graphitic Carbon Nitride to Construct p–n Homojunctions for Enhanced Photocatalytic Hydrogen Production

Graphitic carbon nitride (g‐C₃N₄) has recently emerged as an attractive photocatalyst for solar energy conversion. However, the photocatalytic activities of g‐C₃N₄ remain moderate because of the insufficient solar‐light absorption and the fast electron–hole recombination. Here, defect‐modified g‐C₃N₄ (DCN) photocatalysts, which are easily prepared under mild conditions and show much extended light absorption with band gaps decreased from 2.75 to 2.00 eV, are reported. More importantly, cyano terminal C?N groups, acting as electron acceptors, are introduced into the DCN sheet edge, which endows the DCN with both n‐ and p‐type conductivities, consequently giving rise to the generation of p–n homojunctions. This homojunction structure is demonstrated to be highly efficient in charge transfer and separation, and results in a fivefold enhanced photocatalytic H₂ evolution activity. The findings deepen the understanding on the defect‐related issues of g‐C₃N₄‐based materials. Additionally, the ability to build homojunction structures by the defect‐induced self‐functionalization presents a promising strategy to realize precise band engineering of g‐C₃N₄ and related polymer semiconductors for more efficient solar energy conversion applications.     

3D Foam Strutted Graphene Carbon Nitride with Highly Stable Optoelectronic Properties

Controlled morphology modulation of graphene carbon nitride (g‐C₃N₄) is successfully realized from bulk to 3D loose foam architecture via the blowing effect of a bubble, which can be controlled by heating rate. The loose foam network is comprised by spatially scaffolded few‐atom‐layer interconnected flakes with the large specific surface area, as supporters to prevent agglomeration and provide a pathway for electron/phonon transports. The photocatalytic performance of 3D foam strutted g‐C₃N₄ toward RhB decomposition and hydrogen evolution is significantly enhanced with the morphology optimization while its excellent optoelectronic properties are maintained simultaneously. Herein, the ultrathin, mono‐, and high‐quality foam g‐C₃N₄ interconnected flakes with controlled layer are facilely obtained through ultrasonic, thus overcoming the drawbacks of a traditional top–down approach, opening a wide horizon for diverse practical usages. Additionally, the layer control mechanism of 3D hierarchical structure has been explored by means of bubble growth kinetics analysis and the density functional theory calculations.     

Unique P?Co?N Surface Bonding States Constructed on g‐C3N4 Nanosheets for Drastically Enhanced Photocatalytic Activity of H2 Evolution

Developing high‐efficiency and low‐cost photocatalysts by avoiding expensive noble metals, yet remarkably improving H₂ evolution performance, is a great challenge. Noble‐metal‐free catalysts containing Co(Fe)? N? C moieties have been widely reported in recent years for electrochemical oxygen reduction reaction and have also gained noticeable interest for organic transformation. However, to date, no prior studies are available in the literature about the activity of N‐coordinated metal centers for photocatalytic H₂ evolution. Herein, a new photocatalyst containing g‐C₃N₄ decorated with CoP nanodots constructed from low‐cost precursors is reported. It is for the first time revealed that the unique P(δ^?)? Co(δ⁺)? N(δ^?) surface bonding states lead to much superior H₂ evolution activity (96.2 µmol h^?1) compared to noble metal (Pt)‐decorated g‐C₃N₄ photocatalyst (32.3 µmol h^?1). The quantum efficiency of 12.4% at 420 nm is also much higher than the record values (≈2%) of other transition metal cocatalysts‐loaded g‐C₃N₄. It is believed that this work marks an important step toward developing high‐performance and low‐cost photocatalytic materials for H₂ evolution.     

Reversible Formation of g‐C3N4 3D Hydrogels through Ionic Liquid Activation: Gelation Behavior and Room‐Temperature Gas‐Sensing Properties

Many unique properties arise when the 3D stacking of layered materials is disrupted, originating nanostructures. Stabilization, and further reorganization of these individual layers into complex 3D structures, can be essential to allow these properties to persist in macroscopic systems. It is demonstrated that a simple hydrothermal process, assisted by ionic liquids (ILs), can convert bulk g‐C₃N₄ into a stable hydrogel. The gelation occurs through delamination of the layered structure, driven by particular interactions between the IL and the carbon nitride sheets, forming an amphiphilic foam‐like network. This study employs spectroscopic and computational tools to unravel the gelation mechanism, and provides a rational approach toward the stabilization of 2D materials in hydrogels. The solution‐processable hydrogels can also be used as building blocks of complex devices. Chemiresistive gas sensors employing g‐C₃N₄ 3D hydrogels exhibit superior response at room temperature, enabling effective gas sensing under low power conditions.     

Dramatic Activity of C3N4/BiPO4 Photocatalyst with Core/Shell Structure Formed by Self‐Assembly

Core/shell structured C₃N₄/BiPO₄ photocatalyst is fabricated via a facile ultrasonic dispersion method. The thickness of the shell may be controlled by tuning the amount of C₃N₄ in the dispersion, which determines the enhanced level of photocatalytic activity. The optimum photocatalytic activity of C₃N₄/BiPO₄ at a weight ratio of 4% (C₃N₄/BiPO₄) under UV irradiation is almost 4.5 times as high as that of reference P25 (TiO₂) and 2.5 times of BiPO₄. More attractively, the dramatic visible light photocatalytic activity is generated due to the C₃N₄ loaded. The enhancement in performance is demonstrated to be the match of lattice and energy level between the C₃N₄ and BiPO₄. This match facilitates the separation and transfer of photogenerated electron–hole pairs at the heterojunction interfaces and may be important for other core/shell structured materials. In addition, this method is expected to be extended for other C₃N₄ loaded materials.     

Tuning the Catalytic Preference of Ruthenium Catalysts for Nitrogen Reduction by Atomic Dispersion

Developing cost‐effective, high‐performance nitrogen reduction reaction (NRR) electrocatalysts is required for the production of green and low‐cost ammonia under ambient conditions. Here, a strategy is proposed to adjust the reaction preference of noble metals by tuning the size and local chemical environment of the active sites. This proof‐of‐concept model is realized by single ruthenium atoms distributed in a matrix of graphitic carbon nitride (Ru SAs/g‐C₃N₄). This model is compared, in terms of the NRR activity, to bulk Ru. The as‐synthesized Ru SAs/g‐C₃N₄ exhibits excellent catalytic activity and selectivity with an NH₃ yield rate of 23.0 µg mg_cat^?1 h^?1 and a Faradaic efficiency as high as 8.3% at a low overpotential (0.05 V vs the reversible hydrogen electrode), which is far better than that of the bulk Ru counterpart. Moreover, the Ru SAs/g‐C₃N₄ displays a high stability during five recycling tests and a 12 h potentiostatic test. Density functional theory calculations reveal that compared to bulk Ru surfaces, Ru SAs/g‐C₃N₄ has more facile reaction thermodynamics, and the enhanced NRR performance of Ru SAs/g‐C₃N₄ originates from a tuning of the d‐electron energies from that of the bulk to a single‐atom, causing an up‐shift of the d‐band center toward the Fermi level.     

Incorporating Graphitic Carbon Nitride (g‐C3N4) Quantum Dots into Bulk‐Heterojunction Polymer Solar Cells Leads to Efficiency Enhancement

Graphitic carbon nitride (g‐C₃N₄) has been commonly used as photocatalyst with promising applications in visible‐light photocatalytic water‐splitting. Rare studies are reported in applying g‐C₃N₄ in polymer solar cells. Here g‐C₃N₄ is applied in bulk heterojunction (BHJ) polymer solar cells (PSCs) for the first time by doping solution‐processable g‐C₃N₄ quantum dots (C₃N₄ QDs) in the active layer, leading to a dramatic efficiency enhancement. Upon C₃N₄ QDs doping, power conversion efficiencies (PCEs) of the inverted BHJ‐PSC devices based on different active layers including poly(3‐hexylthiophene‐2,5‐diyl):[6,6]‐phenyl‐C61‐butyric acid methyl ester (P3HT:PC₆₁BM), poly(4,8‐bis‐alkyloxybenzo(l,2‐b:4,5‐b′)dithiophene‐2,6‐diylalt‐(alkyl thieno(3,4‐b)thiophene‐2‐carboxylate)‐2,6‐diyl):[6,6]‐phenyl C₇₁‐butyric acid methyl ester (PBDTTT‐C:PC₇₁BM), and poly[4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene‐co‐3‐fluorothieno [3,4‐b]thiophene‐2‐carboxylate] (PTB7‐Th):PC₇₁BM reach 4.23%, 6.36%, and 9.18%, which are enhanced by ≈17.5%, 11.6%, and 11.8%, respectively, compared to that of the reference (undoped) devices. The PCE enhancement of the C₃N₄ QDs doped BHJ‐PSC device is found to be primarily attributed to the increase of short‐circuit current (J_sc), and this is confirmed by external quantum efficiency (EQE) measurements. The effects of C₃N₄ QDs on the surface morphology, optical absorption and photoluminescence (PL) properties of the active layer film as well as the charge transport property of the device are investigated, revealing that the efficiency enhancement of the BHJ‐PSC devices upon C₃N₄ QDs doping is due to the conjunct effects including the improved interfacial contact between the active layer and the hole transport layer due to the increase of the roughness of the active layer film, the facilitated photoinduced electron transfer from the conducting polymer donor to fullerene acceptor, the improved conductivity of the active layer, and the improved charge (hole and electron) transport.     

Smart Hybrids of Zn2GeO4 Nanoparticles and Ultrathin g‐C3N4 Layers: Synergistic Lithium Storage and Excellent Electrochemical Performance

Smart hybrids of Zn₂GeO₄ nanoparticles and ultrathin g‐C₃N₄ layers (Zn₂GeO₄/g‐C₃N₄ hybrids) are realized by a facile solution approach, where g‐C₃N₄ layers act as an effective substrate for the nucleation and subsequent in situ growth of Zn₂GeO₄ nanoparticles. A synergistic effect is demonstrated on the two building blocks of Zn₂GeO₄/g‐C₃N₄ hybrids for lithium storage: Zn₂GeO₄ nanoparticles contribute high capacity and serve as spacers to isolate the ultrathin g‐C₃N₄ layers from restacking, resulting in expanded interlayer and exposed vacancies with doubly bonded nitrogen for extra Li‐ion storage and diffusion pathway; 2D g‐C₃N₄ layers, in turn, minimize the strain of particles expansion and prevent the formation of unstable solid electrolyte interphase, leading to highly reversible lithium storage. Benefiting from the remarkable synergy, the Zn₂GeO₄/g‐C₃N₄ hybrids exhibit highly reversible capacity of 1370 mA h g^?1 at 200 mA g^?1 after 140 cycles and excellent rate capability of 950 mA h g^?1 at 2000 mA g^?1. The synergistic effect originating from the hybrids brings out excellent electrochemical performance, and thus casts new light on the development of high‐energy and high‐power anode materials.     

Cocatalyst‐Free Photocatalysts for Efficient Visible‐Light‐Induced H2 Production: Porous Assemblies of CdS Quantum Dots and Layered Titanate Nanosheets

Highly efficient, visible‐light‐induced H₂ generation can be achieved without the help of a Pt cocatalyst by new hybrid photocatalysts, in which CdS quantum dots (QDs) (particle size ≈2.5 nm) are incorporated in the porous assembly of sub‐nanometer‐thick layered titanate nanosheets. Due to the very‐limited crystal dimension of component semiconductors, the electronic structure of CdS QDs is strongly coupled with that of the layered titanate nanosheets, leading to an efficient electron transfer between them and the enhancement of the CdS photostability. As a consequence of the promoted electron transfer, the photoluminescence of CdS QDs is nearly quenched after hybridization, indicating the almost‐suppression of electron‐hole recombination. These Pt‐cocatalyst‐free, CdS‐layered titanate nanohybrids show much‐higher photocatalytic activity for H₂ production than the precursor CdS QDs and layered titanate, which is due to the increased lifetime of the electrons and holes, the decrease of the bandgap energy, and the expansion of the surface area upon hybridization. The observed photocatalytic efficiency of these Pt‐free hybrids (≈1.0 mmol g^?1 h^?1) is much greater than reported values of other Pt‐free CdS‐TiO₂ systems. This finding highlights the validity of 2D semiconductor nanosheets as effective building blocks for exploring efficient visible‐light‐active photocatalysts for H₂ production.     

Carbon Nanotube–Graphitic Carbon Nitride Hybrid Films for Flavoenzyme‐Catalyzed Photoelectrochemical Cells

In green plants, solar‐powered electrons are transferred through sophistically arranged photosystems and are subsequently channelled into the Calvin cycle to generate chemical energy. Inspired by the natural photosynthetic scheme, a photoelectrochemical cell (PEC) is constructed configured with protonated graphitic carbon nitride (p‐g‐C₃N₄) and carbon nanotube hybrid (CNT/p‐g‐C₃N₄) film cathode, and FeOOH‐deposited bismuth vanadate (FeOOH/BiVO₄) photoanode for the production of industrially useful chiral alkanes using an old yellow enzyme homologue from Thermus scotoductus (TsOYE). In the biocatalytic PEC platform, photoexcited electrons provided by the FeOOH/BiVO₄ photoanode are transferred to the robust and self‐standing CNT/p‐g‐C₃N₄ hybrid film that electrocatalytically reduces flavin mononucleotide (FMN) mediator. The p‐g‐C₃N₄ promotes a two‐electron reduction of FMN coupled with an accelerated electron transfer by the conductive CNT network. The reduced FMN subsequently delivers the electrons to TsOYE for the highly enantioselective conversion of ketoisophorone to (R)‐levodione. Under light illumination (>420 nm) and external bias, (R)‐levodione is synthesized with the enantiomeric excess value of above 83%, not influenced by the scale of applied bias, simultaneously exhibiting stable and high current efficiency. The results suggest that the biocatalytic PEC made up of economical materials can selectively synthesize high‐value organic chemicals using water as an electron donor.     

Boosting Performance of Non‐Fullerene Organic Solar Cells by 2D g‐C3N4 Doped PEDOT:PSS

The power‐conversion efficiency (PCE) of single‐junction organic solar cells (OSCs) has exceeded 16% thanks to the development of non‐fullerene acceptor materials and morphological optimization of active layer. In addition, interfacial engineering always plays a crucial role in further improving the performance of OSCs based on a well‐established active‐layer system. Doping of graphitic carbon nitride (g‐C₃N₄) into poly(3,4‐ethylene‐dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as a hole transport layer (HTL) for PM6:Y6‐based OSCs is reported, boosting the PCE to almost 16.4%. After being added into the PEDOT:PSS, the g‐C₃N₄ as a Bronsted base can be protonated, weakening the shield effect of insulating PSS on conductive PEDOT, which enables exposures of more PEDOT chains on the surface of PEDOT:PSS core‐shell structure, and thus increasing the conductivity. Therefore, at the interface between g‐C₃N₄ doped HTL and PM6:Y6 layer, the charge transport is improved and the charge recombination is suppressed, leading to the increases of fill factor and short‐circuit current density of devices. This work demonstrates that doping g‐C₃N₄ into PEDOT:PSS is an efficient strategy to increase the conductivity of HTL, resulting in higher OSC performance.     

Patterned Carbon Nitride–Based Hybrid Aerogel Membranes via 3D Printing for Broadband Solar Wastewater Remediation

Controlled scalable assembly of 2D building blocks into macroscopic 3D architectures is highly significant. However, the assembly of g‐C₃N₄ into tailored, 3D architectures is not yet reported. Here, a 3D printing methodology to enable the programmable construction of carbon nitride–based hybrid aerogel membranes with patterned macroscopic architectures is proposed. g‐C₃N₄ nanosheets (CNNS) are used as the building block, and sodium alginate (SA) increases the viscosity of the ink to obtain the desired rheological properties. Three printing routes, including printing directly in air and in the supporting reservoirs composed of CaCl₂/glycerol solution or Pluronic F127, are demonstrated for printing versatility. The printed Au nanobipyramid–CNNS–SA hybrid aerogels exhibit broadband visible‐light absorption and superior solar wastewater remediation performance with excellent cyclic stability and easy manipulation features. Remarkably, the activity of the 3D‐printed aerogel is about 2.5 times of that of the contrast sample, attributing to the enhanced liquid velocity and solution diffusion efficiency because of the 3D‐printed structure, which is demonstrated by experimental and theoretical simulations. This approach can be extended to the macroscopic assembly of other 2D materials for myriad applications.     

Gold Nanoparticles and g‐C3N4‐Intercalated Graphene Oxide Membrane for Recyclable Surface Enhanced Raman Scattering

Toxic organic pollutants in the aquatic environment cause severe threats to both humans and the global environment. Thus, the development of robust strategies for detection and removal of these organic pollutants is essential. For this purpose, a multifunctional and recyclable membrane by intercalating gold nanoparticles and graphitic carbon nitride into graphene oxide (GNPs/g‐C₃N₄/GO) is fabricated. The membranes exhibit not only superior surface enhanced Raman scattering (SERS) activity attributed to high preconcentration ability to analytes through π–π and electrostatic interactions, but also excellent catalytic activity due to the enhanced electron–hole separation efficiency. These outstanding properties allow the membrane to be used for highly sensitive detection of rhodamine 6G with a limit of detection of 5.0 × 10^?14m and self‐cleaning by photocatalytic degradation of the adsorbed analytes into inorganic small molecules, thus achieving recyclable SERS application. Furthermore, the excellent SERS activity of the membrane is demonstrated by detection of 4‐chlorophenol at less than nanomolar level and no significant SERS or catalytic activity loss was observed when reusability is tested. These results suggest that the GNPs/g‐C₃N₄/GO membrane provides a new strategy for eliminating traditional, single‐use SERS substrates, and expands practical SERS application to simultaneous detection and removal of environmental pollutants.     

Cocatalyst Engineering with Robust Tunable Carbon-Encapsulated Mo-Rich Mo/Mo2C Heterostructure Nanoparticle for Efficient Photocatalytic Hydrogen Evolution

Cocatalyst engineering with non-noble metal nanomaterials can play a vital role in low-cost, sustainable, and large-scale photocatalytic hydrogen production. This research adopts slow carburization and simultaneous hydrocarbon reduction to synthesize carbon-encapsulated Mo/Mo₂C heterostructure nanoparticles, namely Mo/Mo₂C@C cocatalyst. Experimental and theoretical investigations indicate that the Mo/Mo₂C@C cocatalysts have a nearly ideal hydrogen-adsorption free energy (ΔG_H*), which results in the accelerated HER kinetics. As such, the cocatalysts are immobilized onto organic polymer semiconductor g-C₃N₄ and inorganic semiconductor CdS, resulting in Mo/Mo₂C@C/g-C₃N₄ and Mo/Mo₂C@C/CdS catalysts, respectively. In photocatalytic hydrogen evolution application under visible light, the Mo/Mo₂C@C with g-C₃N₄ and CdS can form the Schottky junctions via appropriate band alignment, greatly suppressing the recombination of photoinduced electron-hole pairs. The surface carbon layer as the conducting scaffolds and Mo metal facilitates electron transfer and electron-hole separation, favoring structural stability and offering more reaction sites and interfaces as electron mediators. As a result, these catalysts exhibit high H₂ production rates of 2.7 mmol h⁻¹ g⁻¹ in basic solution and 98.2 mmol h⁻¹ g⁻¹ in acidic solution, respectively, which is significantly higher than that of the bench-mark Pt-containing catalyst. The proposed cocatalyst engineering approach is promising in developing efficient non-noble metal cocatalysts for rapid hydrogen production.