Large Current Density Research Articles

Constructing quasi‐amorphous cobalt oxyhydroxide nanowires with synergy of anion and cation via ion exchange reconstruction for large-current–density oxygen generation

Deep insight into the synergy between anion and cation aids in the maximization of catalytic activity and the rational exploitation of efficient oxygen-evolving catalysts. However, how to use ion exchange reconstruction to devise highly active and cost-efficient oxygen evolution reaction (OER) catalysts with anion and cation synergies for water electrolysis is rarely reported. Herein, the cobalt triphosphide (CoP3) nanowires are elaborately devised as a component-flexible precatalyst for directing an anodic reconfiguration with Ni cation exchange to construct a highly active and quasi‐amorphous cobalt oxyhydroxide (CoOOH) catalyst integrated with cation (Ni) substitution and oxyanion (PO43-) decoration (denoted by R-(Ni)CoP3). Interestingly, the structural evolution and the Ni cation exchange processes are captured through various in/ex situ techniques. The resultant R-(Ni)CoP3 nanowires display a splendid activity with low overpotentials of 406 and 420 mV to respectively deliver industrial grade current densities of 1000 and 1500 mA cm−2, and an outstanding stability over 300 h at a large current density of 500 mA cm−2, superior to most progressive cobalt-based OER materials and the benchmark IrO2. The combination of theoretical calculations with experimental studies demonstrate that the synergy of cation (Ni) substitution and oxyanion (PO43-) decoration can significantly modulate the electronic states of CoOOH and optimize the adsorption free energy of OER intermediates, thus immensely expediting the kinetics process and enhancing the charge transfer ability and the intrinsic OER activity. This research suggests ion-regulatory reconfiguration as a flexible and changeable strategy to construct various efficient and advanced catalysts for water electrolysis and beyond.

From Quinary Co–Cu–Mo–Pd–Re Materials Libraries to Gas Diffusion Electrodes for Alkaline Hydrogen Evolution

AbstractDeveloping a hydrogen evolution reaction (HER) electrocatalyst that can steadily drive a large current density is of great significance for industrial electrochemical water‐splitting technology. Herein, the compositionally complex noble‐metal‐lean system Co–Cu–Mo–Pd–Re is investigated for alkaline HER by a scanning droplet cell‐assisted high‐throughput screening of co‐sputtered thin‐film material libraries. The identified hit compositions are used to prepare a catalyst‐coated Ni foam‐based layer that is hot‐pressed with a specifically designed PEEK‐covered carbon‐based gas diffusion layer to obtain a novel‐design gas diffusion electrode (GDE). H2 bubbles that collect on the electrode surface are effectively reduced by controlling the hydrophobicity of the catalyst layer of the GDE, hence enabling a high current (−1 A cm−2) operation for HER in alkaline water electrolysis.

Novel NaNbO3-based relaxors featuring ultrahigh energy storage performance

Ferroelectric ceramics with ultrahigh power density and fast charging/discharging are attracting increasing attention. The practical application of most antiferroelectric ceramics in current electronics is significantly limited by their poor recoverable energy storage density. Here, a novel system ceramic of (1-x) Na0.84Ca0.16Nb0.84Ti0.16O3-xBiZn2/3Nb1/3O3 (NCNT-xBZN) solid solutions, possessing a giant Wrec∼7.05 J cm−3 and excellent conversion efficiency (η)∼83.7% under 53 kV mm−1, was synthesized to exhibit superior stability with changing temperature, frequency and fatigue behavior, together with the large current density (CD=571.8 A cm−2), ultrahigh power density (PD=85.7 MW cm−3) and ultrafast discharge rate (∼200 ns). These outstanding properties are attributed to the phase transformation from the AFE R to the FE Q phase, accompanied by the smashing of sub-microdomains into polar nanoregions, as the BZN content raises. The experimental results disclose that the synergistic effect of the highly dynamic response of polar nanoregions and the local lattice distortion arising from the disruption of long-range polar ordering by heterovalent ion filling generates a delayed saturation polarization with a strong relaxor behavior, thereby optimizing the energy storage density. The unique combination, together with a simple synthesis strategy, offers a refreshing strategy for the development of dielectric materials.

Ultra-High Performance of In Situ Constructed Trimetallic (Pd, Fe, Co) Nanoparticles on Carbon Paper as an Electrocatalyst for Large Current Density Oxygen Evolution Reaction in Alkaline Seawater

Seawater electrocatalysis holds significant promise as a technology for hydrogen production. A simple and low-cost impregnation-hydrothermal and thermal reduction strategy was used to synthesize in situ constructed three-dimensional porous trimetallic (Pd, Fe, and Co) anchored on a cheap and high-conducting carbon paper (CP) electrode for water electrolysis in alkaline media. The fabricated PdFeCo1−xONPs@CP electrode had super-hydrophilic and superaerophobic properties, allowing for the efficient removal of oxygen bubbles from the electrode surface due to the close interaction between the electrode and electrolyte. Furthermore, the synergistic effect of trimetallics and CP-fibers significantly increased OER intrinsic activity. PdFeCo1−xONPs@CP catalyst demonstrated critical low overpotentials of 220 and 300 mV, resulting in an extraordinarily high current density of 100 mA cm−2. For the full cell overall water splitting performance, cell overpotentials as low as 140 and 151 mV were needed to drive 10 mA cm−2 in seawater and alkaline solution electrolytes.

Unraveling Paradoxical Effects of Large Current Density on Zn Deposition.

Aqueous zinc-based batteries (ZBs) have been widely investigated owing to their intrinsic safety, low cost, and simple assembly. However, the actual behavior of Zn deposition under large current density is still a severe issue associated with obscure mechanism interpretation of ZBs under high loading. Here, differing from the conventional understanding that short circuit is induced by dendrite penetrating under large current density (10-100mA cm-2), the separator permeation effect is unraveled to illustrate the paradox between smooth deposition and short lifespan. Generally, a dense plating morphology is achieved under large current density because of intensive nuclei and boosted plane growth. Nevertheless, in the scenes applying separators, the multiplied local current density derived from narrow separator channels leads to rapid Zn2+ exhaustion, converting the Zn deposition mode from nucleation control to concentration control, which eventually results in separator permeation and short circuit. This effect is validated in other aqueous metal anodes (Cu, Sn, Fe) and receives similar results. Based on the understanding, a micro-pore (150µm) sponge foam is proposed as separators for large-current anodes to provide broader Zn2+ path and mitigate the separator permeation effect. This work provides unique perspectives on coordinating fast-charging ability and anode stability of ZBs.

Superhydrophilic NiFe-LDH@Co9S8-Ni3S2/NF heterostructures for high-current-density freshwater/seawater oxidation electrocatalysts

Designing oxygen evolution reaction (OER) electrocatalysts with high efficiency and stability at large current densities is paramount for achieving hydrogen production through water splitting. In this study, a heterostructured NiFe-LDH coating Co9S8-Ni3S2 grown on nickel foam (NiFe-LDH@Co9S8-Ni3S2/NF) was successfully synthesized. The distinctive hierarchical structures featuring abundant heterointerfaces can effectively expose abundant active sites. The synergistic effect and strong electronic interaction between Co9S8-Ni3S2 and NiFe-LDH can enhance the intrinsic OER activity. Furthermore, the superhydrophilic characteristic of NiFe-LDH@Co9S8-Ni3S2/NF favors close contact between the electrode and electrolyte. Due to these advantages, NiFe-LDH@Co9S8-Ni3S2/NF can provide distinguished OER activity with low overpotentials of 274 mV in alkaline freshwater and 298 mV in alkaline seawater at 1000 mA cm−2, along with outstanding stability at high current density of 500 mA cm−2 over 200 h in both solutions. This study offers a valuable insight into fabricating high-performance OER electrocatalysts for seawater electrolysis in industrial applications.

Hierarchical porous graphene nanosheets derived from moso bamboo with superior supercapacitor performance

Moso bamboo is regarded as a kind of biomass resource with abundant reserves in nature, and how to achieve its high-value utilization is one of the important research topics widely concerned by the academic community. In this work, hierarchical porous graphene nanosheets with wrinkled structures derived from the natural moso bamboo is obtained via a compact two-step processing method including pyrolysis and chemical activation. The as-prepared ABC-950 possess a large specific surface area of 1758 m2 g−1, pore volume of 1.55 cm3 g−1, mesopores ratio of 75.5 % and high graphitization degree with ID/IG as low as 0.43. With these merits, as the electrode material for supercapacitor, the ABC-950 exhibits a high specific capacitance of 459.4 F g−1 at 1 A g−1 and an excellent rate performance of 82.3 % in 6 M KOH electrolyte. Moreover, the ABC-950 based symmetric supercapacitor shows superior specific capacitance of 112.3 F g−1 at 0.5 A g−1 and an attractive energy density of 15.6 Wh·kg−1 at 250 W kg−1. Moreover, outstanding capacitance retention of about 102.1 % even after 30,000 charge-discharge cycles at a large current density of 10 A g−1. Our work offers a promising method to easily transform moso bamboo into porous graphene nanosheets for the electric energy storage.

Vertically Staggered Porous Ni2P/Fe2P Nanosheets with Trace Ru Doping as Bifunctional Electrocatalyst for Alkaline Seawater Splitting

AbstractDesigning a bifunctional electrocatalyst with high performance and low‐cost is of great significance to promote the large‐scale application of water splitting. Herein, porous Ru‐Ni2P/Fe2P heterojunction nanosheets with a vertically staggered structure are rationally fabricated to boost alkaline seawater splitting under large current densities. The Ru‐Ni2P/Fe2P catalyst exhibits remarkable activity in alkaline media, requiring only 274 and 331 mV at a large current density of 1000 mA cm−2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Additionally, the NiFeOOH layer formed on the surface of Ru‐Ni2P/Fe2P is proposed as the active phase to promote the OER performance. Furthermore, an anion exchange membrane (AEM) electrolyzer assembled by Ru‐Ni2P/Fe2P electrocatalyst exhibits excellent long‐term durability over 100 h, achieving a current density of 500 mA−2 at 2.0 V in alkaline seawater at 60 °C. Theoretical calculations reveal that the Ni2P/Fe2P heterojunction integration with trace Ru leads to balanced adsorption and desorption properties. Moreover, the active sites of Ru‐Ni2P/Fe2P are confirmed, in which Ni site is favorable for HER and Fe site is conducive to OER. This work provides an insight into designing a highly efficient and cost‐effective bifunctional electrocatalyst for overall seawater splitting.

Eliminating the Adverse Impact of Composition Modulation in Perovskite Light-Emitting Diodes toward Ultra-High Brightness and Stability.

Excess ammonium halides as composition additives are widely employed in perovskite light-emitting diodes (PeLEDs), aiming to achieve high performance by controlling crystallinity and passivating defects. However, an in-depth understanding of whether excess organoammonium components affect the film physical/electrical properties and the resultant device instability is still lacking. Here, the trade-off between the performance and stability in high-efficiency formamidinium lead iodide (FAPbI3)-based PeLEDs with excess ammonium halides is pointed, and the underlying mechanism is explored. Systematic experimental and theoretical studies reveal that excess halide salt-induced ion-doping largely alters the PeLEDs properties (e.g., carrier injection, field-dependent ion-drifting, defect physics, and phase stability). A surface clean assisted cross-linking strategy is demonstrated to eliminate the adverse impact of composition modulation and boost the operational stability without sacrificing the efficiency, achieving a high efficiency of 23.6%, a high radiance of 964 W sr-1 m-2 (The highest value for FAPbI3 based PeLEDs), and a prolong lifetime of 106.1 h at large direct current density (100mA cm-2), concurrently. The findings uncovered an important link between excess halide salts and the device performance, providing a guideline for rational design of stable, bright, and high efficiency PeLEDs.

Synthesis and characteristics of a monocrystalline GaAs/β-Ga2O3p-n heterojunction

Beta phase-gallium oxide (β-Ga2O3) is an emerging ultrawide bandgap semiconductor but lacks efficient p-type doping, which hinders development of high-performance bipolar heterojunction devices. This study introduces the synthesis and characterization of a monocrystalline GaAs/β-Ga2O3p-n heterojunction, employing advanced semiconductor grafting technology. The heterojunction was innovatively fabricated by grafting a p-type GaAs single crystal nanomembrane to an Al2O3-coated n-type β-Ga2O3 epitaxial substrate. The synthesized heterojunction was comprehensively characterized. The band alignment of grafted GaAs/β-Ga2O3p-n heterojunction was experimentally constructed through X-ray photoelectron spectroscopy (XPS), and the result is in accordance with the theorical prediction based on the electron affinity rule. The resulting GaAs/β-Ga2O3p-n diodes built on this heterojunction exhibit remarkable performance metrics, including an ideality factor of 1.23, a high rectification ratio of 8.04 × 109 at ± 4 V, and a turn on voltage at 2.35 V. Furthermore, at + 5 V, the diode displays a large current density of 2500 A/cm2 along with a low ON resistance of 2 mΩ∙cm2. This study marks the first successful demonstration of a high-quality grafted GaAs/β-Ga2O3p-n heterojunction, establishing a critical building block for the further development of bipolar Ga2O3-based device applications such as diodes, transistors, and thyristors.

Biomimetic-Mineralization-Assisted Self-Activation Creates a Delicate Porous Structure in Carbon Material for High-Rate Sodium Storage.

Porous carbons have shown their potential in sodium-ion batteries (SIBs), but the undesirable initial Coulombic efficiency (ICE) and rate capability hinder their practical application. Herein, learning from nature, we report an efficient method for fabricating a carbon framework (CK) with delicate porous structural regulation by biomimetic mineralization-assisted self-activation. The abundant pores and defects of the CK anode can improve the ICE and rate performance of SIBs in ether-based electrolytes, whereas they are confined in carbonate ester-based electrolytes. Notably, ether-based electrolytes enable CK anode to possess excellent ICE (82.9%) and high-rate capability (111.2 mAh g-1 at 50 A g-1). Even after 5500 cycles at a large current density of 10 A g-1, the capacity retention can still be maintained at 73.1%. More importantly, the full cell consisting of the CK anode and Na3V2(PO4)3 cathode delivers a high energy density of 204.4 Wh kg-1, with a power density of 2828.2 W kg-1. Such outstanding performance of the CK anode is attributed to (1) hierarchical pores, oxygen doping, and defects that pave the way for the transportation and storage of Na+, further enhancing ICE; (2) a high-proportion NaF-based solid-electrolyte-interphase (SEI) layer that facilitates Na+ storage kinetics in ether-based electrolytes; and (3) ether-based electrolytes that determine Na+ storage kinetics further to dominate the performance of SIBs. These results provide compelling evidence for the promising potential of our synthetic strategy in the development of carbon-based materials and ether-based electrolytes for electrochemical energy storage.

Realizing the dendrite-free sulfide-based all-solid-state Li metal battery by surface design

Although the ultrahigh ionic conductivity of sulfide-type solid electrolytes is comparable to that of liquid electrolytes, the low critical current density (CCD) limits the practical application of solid-state lithium (Li) metal batteries. The insufficient Li0 self-diffusion in solid Li leads to the voids that form at the interface at a large stripping current density, which results in interface contact loss and the increase of local current density. Herein, an artificial hybrid interphase layer dominated by Li3Sb and LiF was constructed on the Li surface to explore the Li plating/stripping behavior at the Li/Li6PS5Cl interface. The Li3Sb alloy provides a fast Li0 diffusion channel to avoid the interfacial voids formation and current focusing, while the electrically insulated LiF acts an electron blocking shield at the Li/Li6PS5Cl interface. Consequently, the symmetric cells reveal a significantly increased CCD of 1.8 mA cm−2 and a stable Li plating/stripping for 1472 h with a high current density of 2 mA cm−2 at 50 °C. Moreover, the all-solid-state Li-SPAN cell with Li3Sb/LiF interphase exhibits good capacity retention of 83.2 % after 120 cycles at 0.5 C, and it also delivers a superior rate performance of 400 mAh g−1 at 5C. The construction of lithium-alloy interphase is a promising alternative to solid-state lithium battery applications.

Chromium-Induced High Covalent Co-O Bonds for Efficient Anodic Catalysts in PEM Electrolyzer.

The proton exchange membrane water electrolyzer (PEMWE), crucial for green hydrogen production, is challenged by the scarcity and high cost of iridium-based materials. Cobalt oxides, as ideal electrocatalysts for oxygen evolution reaction (OER), have not been extensively applied in PEMWE, due to extremely high voltage and poor stability at large current density, caused by complicated structural variations of cobalt compounds during the OER process. Thus, the authors sought to introduce chromium into a cobalt spinel (Co3O4) catalyst to regulate the electronic structure of cobalt, exhibiting a higher oxidation state and increased Co-O covalency with a stable structure. In-depth operando characterizations and theoretical calculations revealed that the activated Co-O covalency and adaptable redox behavior are crucial for facilitating its OER activity. Both turnover frequency and mass activity of Cr-doped Co3O4 (CoCr) at 1.67V (vs RHE) increased by over eight times than those of as-synthesized Co3O4. The obtained CoCr catalyst achieved 1500mA cm-2 at 2.17V and exhibited notable durability over extended operation periods - over 100h at 500 mA cm-2 and 500h at 100 mA cm-2, demonstrating promising application in the PEMWE industry.

Multiphase Fe-doped Ni3S2/MoOx electrocatalyst prepared by facile one-step hydrothermal for full-cell water splitting: Effect of Mo on physical and electrochemical properties

Herein, we develop a multiphase strategy to improve the HER performance by incorporating the MoOx phase with the addition of MoCl5 during the one-step hydrothermal. Adding MoCl5 at 0.5 mmol (MFN-0.5) yields the best HER performance, with an overpotential of 261 mV at a current density of 100 mA/cm2. The MFN-0.5 catalyst exhibits excellent performance for both HER and OER, enabling it to drive full-cell water splitting with cell potentials of 1.50 and 1.71 V at 10 and 100 mA/cm2, respectively. We further scale up the MFN-0.5 (4 ×4 cm2) for a single stack-cell electrolyzer, requiring a cell potential of 1.85 V to achieve a large current density of 250 mA/cm2. Incorporating the MoOx phase accelerates the water dissociation step and protects the metal sulfide surface from oxidation under anodization in an alkaline environment. Our findings offer a promising approach for developing highly efficient catalysts for electrolytic water-splitting applications.

Boost alkaline hydrogen evolution reaction by intermetallic charge transfer in perovskite ruthenate encapsulated in ZIF-67 derived cobalt sulfide nanoparticles

Constructing and manipulating heterostructure is an effective strategy to prepare electrocatalysts with excellent performance for water electrolysis. Herein, an efficient alkaline hydrogen evolution reaction (HER) electrocatalysts, Co3S4-embedded in carbon-encapsulated BaRuO3 (BaRuO3@CS-0.1), was synthesized through the sacrificial template method of ZIF-67 encapsulated BaRuO3 precursors. By inheriting the exceptional merits of different ingredients, this heterostructure catalyst BaRuO3@CS-0.1 enables intermetallic charge transfer between Ru and Co with boosted HER kinetics, and thus displaying higher catalytic activity towards HER, as evidenced by the intensively theoretical calculations and experimental measurements. BaRuO3@CS-0.1 exhibits excellent HER performance, with the lowered overpotentials of 26 mV to achieve 10 mA cm−2 in comparison to the pristine BaRuO3 (51 mV), which is also superior to Pt/C catalyst at large current density. Moreover, this heterostructure also demonstrates comparable oxygen evolution reaction (OER) activities with the representative electrocatalysts, delivering current densities of 10 mA cm−2 at a potential of 1.546 V for overall water splitting. These findings provide a rational route to optimize the performance of bulk electrocatalysts and endow them with richer electrochemical activity through this composite strategy.

High-entropy layered double hydroxide catalyst decorated with Ag nanoparticles for highly efficient water oxidation

Highly efficient and stable catalysts for oxygen evolution reaction (OER) are urgently needed for water splitting. Here, a novel FeNiMnCuAl LDH catalyst decorated with Ag nanoparticles for OER was fabricated by the hydrothermal and chemical reduction method. The heterostructure catalyst exhibits a low over potential of 208 mV to achieve a current density of 10 mA cm−2 and a low Tafel slope of 60 mV dec−1. In addition, it has an excellent long-term stability for more than 50 h at a large current density of ∼100 mA cm−2. By combining the experiment and theoretical calculation, it shows that the increased conductivity and optimized energy barrier are responsible for the boosted intrinsic activity. This work not only provides a promising electrocatalyst but also broadens the application field of high-entropy materials.

Self-Catalyzed Growth of Co4N and N-Doped Carbon Nanotubes toward Bifunctional Cathode for Highly Safe and Flexible Li-Air Batteries.

The practical application of high-energy density lithium-oxygen (Li-O2) batteries is severely impeded by the notorious cycling stability and safety, which mainly comes from slow kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at cathodes, causing inferior redox overpotentials and reactive lithium metal in flammable liquid electrolyte. Herein, a bifunctional electrode, a safe gel polymer electrolyte (GPE), and a robust lithium anode are proposed to alleviate above problems. The bifunctional electrode is composed of N-doped carbon nanotubes (N-CNTs) and Co4N by in situ chemical vapor deposition self-catalyzed growth on carbon cloth (N-CNTs@Co4N@CC). The self-supporting, binder-free N-CNTs@Co4N@CC electrode has a strong and stable three-dimensional (3D) interconnected conductive structure, which provides interconnectivity between the active sites and the electrode to promote the transfer of electrons. Furthermore, the N-CNT-intertwined Co4N ensures efficient catalytic activity. Hence, the electrode demonstrates improved electrochemical properties even under a large current density (2000 mA g-1) and long cycling operation (250 cycles). Moreover, a highly safe and flexible rechargeable cell using the 3D N-CNTs@Co4N@CC electrode, GPE, and robust lithium anode design has been explored. The open circuit voltage is stable at ∼3.0 V even after 9800 cycles, which proves the mechanical durability of the integrated GPE cell. The stable cable-type Li-air battery was demonstrated to stably drive the light-emitting diodes (LEDs), highlighting the reliability for practical use.

Aluminum-induced electron structure on nickel phosphide for effective hydrazine‑assisted water splitting at large current density

Hydrazine-assisted water electrolysis emerges as a promising strategy to replace conventional device for effective hydrogen generation. Limited to the great difference of intermediate adsorption energy for hydrogen evolution reaction (HER) and hydrazine oxidation reaction (HzOR), the design and fabrication of bifunctional catalysts is still a knotty challenge in industrial conditions. Herein, Al-doped Ni2P nanoflower architecture grown in-situ on nickel foam (Al-Ni2P/NF) is fabricated through the combination of hydrothermal process and subsequent phosphorization treatment. Ascribed to the redistribution of electron state and optimization of reaction intermediate energy induced by Al, Al-Ni2P/NF expresses distinguished bifunctional catalytic performance with ultralow potentials of −205 and 300 mV at 500 mA cm−2 for HER and HzOR, respectively. When integrated into hydrazine-assisted water splitting as both the anode and cathode, only 0.717 V is required to reach a large current density of 500 mA cm−2. Specially, a novel integrated system driven entirely by sustainable solar energy is proposed, generating energy-saving hydrogen and purify hydrazine-containing sewage simultaneously. This work provides an attracting and practical path for accelerating the development of hydrogen economy.

Strong electronic coupling of NiCo2O4 and CeO2 regulates the nucleation and decomposition of Li2CO3 for high-rate performance Li–CO2 batteries

The sluggish CO2 reduction/evolution kinetics at the cathode severely hamper the industrial applications of Li–CO2 batteries, especially under large current densities. Herein, NiCo2O4/CeO2 with a strong electron coupling effect is prepared via solvothermal method and calcination to realize the rapid kinetics of discharge and charge processes. The electronic character of the catalyst and the growth behavior of Li2CO3 are investigated through density functional theory (DFT) and experiments, elucidating the reaction mechanism of Li–CO2 battery. The results demonstrate that the strong electronic coupling of NiCo2O4 and CeO2 enhances the intrinsic activity of the catalyst and promotes the generation of membrane-like Li2CO3 with good reversibility, thereby enhancing battery performance at a large current density. Consequently, NiCo2O4/CeO2 achieved a large specific capacity of 7767 mAh g−1 under 2000 mA g−1 and could be stably cycled more than 240 times, outperforming most reported metal-based catalysts. This work underscores the important role of strong electronic coupling in facilitating the formation and decomposition of Li2CO3, providing valuable insight for designing cathode catalysts with high-rate properties for Li–CO2 batteries.

Vertical Cross-Alignments of 2D Semiconductors with Steered Internal Electric Field for Urea Electrooxidation via Balancing Intermediates Adsorption.

Single-component electrocatalysts generally lead to unbalanced adsorption of OH- and urea during urea oxidation reaction (UOR), thus obtaining low activity and selectivity especially when oxygen evolution reaction (OER) competes at high potentials (>1.5 V). Herein, a cross-alignment strategy of in situ vertically growing Ni(OH)2 nanosheets on 2D semiconductor g-C3N4 is reported to form a hetero-structured electrocatalyst. Various spectroscopy measurements including in situ experiments indicate the existence of enhanced internal electric field at the interfaces of vertical Ni(OH)2 and g-C3N4 nanosheets, favorable for balancing adsorption of reaction intermediates. This heterojunction electrocatalyst shows high-selectivity UOR compared to pure Ni(OH)2, even at high potentials (>1.5 V) and large current density. The computational results show the vertical heterojunction could steer the internal electric field to increase the adsorption of urea, thus efficiently avoiding poisoning of strongly adsorbed OH- on active sites. A membrane electrode assembly (MEA)-based electrolyzer with the heterojunction anode could operate at an industrial-level current density of 200 mA cm-2. This work paves an avenue for designing high-performance electrocatalysts by vertical cross-alignments of active components.