To utilize intermittent renewable energy as well as achieve the goals of peak carbon dioxide emissions and carbon neutrality, various electrocatalytic devices have been developed. However, the electrocatalytic reactions, e.g., hydrogen evolution reaction/oxygen evolution reaction in overall water splitting, polysulfide conversion in lithium–sulfur batteries, formation/decomposition of lithium peroxide in lithium–oxygen batteries, and nitrate reduction reaction to degrade sewage, suffer from sluggish kinetics caused by multielectron transfer processes. Owing to the merits of accelerated charge transport, optimized adsorption/desorption of intermediates, raised conductivity, regulation of the reaction microenvironment, as well as ease to combine with geometric characteristics, the built-in electric field (BIEF) is expected to overcome the above problems. Here, we give a Review about the very recent progress of BIEF for efficient energy electrocatalysis. First, the construction strategies and the characterization methods (qualitative and quantitative analysis) of BIEF are summarized. Then, the up-to-date overviews of BIEF engineering in electrocatalysis, with attention on the electron structure optimization and reaction microenvironment modulation, are analyzed and discussed in detail. In the end, the challenges and perspectives of BIEF engineering are proposed. This Review gives a deep understanding on the design of electrocatalysts with BIEF for next-generation energy storage and electrocatalytic devices. 

Designing a Built-In Electric Field for Efficient Energy Electrocatalysis

Single-atom nanozymes (SAzymes), with individually isolated metal atom as active sites, have shown tremendous potential as enzyme-based drugs for enzymatic therapy. However, using SAzymes in tumor theranostics remains challenging because of deficient enzymatic activity and insufficient endogenous H2O2. We develop an external-field-enhanced catalysis by an atom-level engineered FeN4-centered nanozyme (FeN4-SAzyme) for radio-enzymatic therapy. This FeN4-SAzyme exhibits peroxidase-like activity capable of catalyzing H2O2 into hydroxyl radicals and converting single-site FeII species to FeIII for subsequent glutathione oxidase-like activity. Density functional theory calculations are used to rationalize the origin of the single-site self-cascade enzymatic activity. Importantly, using X-rays can improve the overall single-site cascade enzymatic reaction process via promoting the conversion frequency of FeII/FeIII. As a H2O2 producer, natural glucose oxidase is further decorated onto the surface of FeN4-SAzyme to yield the final construct GOD@FeN4-SAzyme. The resulting GOD@FeN4-SAzyme not only supplies in situ H2O2 to continuously produce highly toxic hydroxyl radicals but also induces the localized deposition of radiation dose, subsequently inducing intensive apoptosis and ferroptosis in vitro. Such a synergistic effect of radiotherapy and self-cascade enzymatic therapy allows for improved tumor growth inhibition with minimal side effects in vivo. Collectively, this work demonstrates the introduction of external fields to enhance enzyme-like performance of nanozymes without changing their properties and highlights a robust therapeutic capable of self-supplying H2O2 and amplifying self-cascade reactions to address the limitations of enzymatic treatment.

Engineering Single-Atom Iron Nanozymes with Radiation-Enhanced Self-Cascade Catalysis and Self-Supplied H2O2 for Radio-enzymatic Therapy.

The construction of heterojunctions is a promising manner to accelerate the separation and transfer of the charge carriers at the interface. Herein, a binary poly(heptazine-triazine) imides (PHI/PTI) with semi-coherent interfaces was fabricated via a facile two-step salt-melt synthetic process. The built-in electric fields at the semi-coherent interface endow prompt exciton splitting and charge carrier separation. Hence, the optimized PHI/PTI-based copolymer presents a high apparent quantum yield (AQY=64%) for visible-light driven hydrogen production, by the aids of K 2 HPO 4 as charge transfer mediator. This study provides physical insights for the rational promotion of the photocatalytic performance from the viewpoint of interfacial engineering of photocatalytic junctions on crystalline carbon nitride based semiconductors.

Improved Charge Separation in Poly(heptazine-triazine) Imides with Semi-coherent Interfaces for Photocatalytic Hydrogen Evolution.

Adsorption and activation of CO2, and high carriers transform efficiency are of great significance for improving the CO2 photoreduction performance. However, electronic structure regulation plays an important role in the dynamical behavior of carriers. In this study, O atoms were successfully introduced into polymeric carbon nitrogen to synthesize an orange O-modified polymeric carbon nitrogen and achieve the rearrangement of electron density distribution, which promotes the adsorption and activation of CO2 and efficient separation and migration of carriers. DFT calculation demonstrates that the O atoms perform as the dominant active sites and reduce the free energy of determining step. Moreover, the introduction of O atoms broadens the light absorption range by changing the electronic layer structure of polymeric carbon nitrogen. Therefore, the fabricated O-modified polymeric carbon nitrogen exhibits significant performance. Under visible light irradiation, the CO generation efficiency achieved a 10-fold boost. We synthesize theory and experiment to highlight the important role of modulating electronic structure in designing photocatalysts. 

Modulating electronic structure of lattice O-modified orange polymeric carbon nitrogen to promote photocatalytic CO2 conversion

Photoelectrochemical (PEC) water splitting is an appealing approach by which to convert solar energy into hydrogen fuel. Polymeric semiconductors have recently attracted intense interest of many scientists for PEC water splitting. The crystallinity of polymer films is regarded as the main factor that determines the conversion efficiency. Herein, potassium poly(heptazine) imide (K-PHI) films with improved crystallinity were in situ prepared on a conductive substrate as a photoanode for solar-driven water splitting. A remarkable photocurrent density of ca. 0.80 mA cm−2 was achieved under air mass 1.5 global illumination without the use of any sacrificial agent, a performance that is ca. 20 times higher than that of the photoanode in an amorphous state, and higher than those of other related polymeric photoanodes. The boosted performance can be attributed to improved charge transfer, which has been investigated using steady state and operando approaches. This work elucidates the pivotal importance of the crystallinity of conjugated polymer semiconductors for PEC water splitting and other advanced photocatalytic applications.

/pdf/high-performance-potassium-poly-heptazine-imide-films-for-1lmmwqfd.pdf

High-performance potassium poly(heptazine imide) films for photoelectrochemical water splitting

Construction of internal electric fields (IEFs) is crucial to realize efficient charge separation for charge-induced redox reactions, such as water splitting and CO2 reduction. However, a quantitative understanding of the charge transfer dynamics modulated by IEFs remains elusive. Here, electron microscopy study unveils that the non-equilibrium photo-excited electrons are collectively steered by two contiguous IEFs within binary (001)/(200) facet junctions of BiOBr platelets, and they exhibit characteristic Gaussian distribution profiles on reduction facets by using metal co-catalysts as probes. An analytical model justifies the Gaussian curve and allows us to measure the diffusion length and drift distance of electrons. The charge separation efficiency, as well as photocatalytic performances, are maximized when the platelet size is about twice the drift distance, either by tailoring particle dimensions or tuning IEF-dependent drift distances. The work offers great flexibility for precisely constructing high-performance particulate photocatalysts by understanding charge transfer dynamics. 

/pdf/unveiling-the-charge-transfer-dynamics-steered-by-built-in-iqcmg3bk.pdf

Unveiling the charge transfer dynamics steered by built-in electric fields in BiOBr photocatalysts

Interface functional groups protected by confinement effect for flexible supercapacitor and capacitive deionization

Two-dimensional polymerized carbon nitride coupled with (001)-facets-exposed titanium dioxide S-scheme heterojunction for photocatalytic degradation of norfloxacin

Jie Sun

Papers

Unveiling the charge transfer dynamics steered by built-in electric fields in BiOBr photocatalysts

Interface functional groups protected by confinement effect for flexible supercapacitor and capacitive deionization

Two-dimensional polymerized carbon nitride coupled with (001)-facets-exposed titanium dioxide S-scheme heterojunction for photocatalytic degradation of norfloxacin

Effect of KBr on electrodeposition of Ag in choline chloride-ethylene glycol deep eutectic solvents

Reactive adsorption desulfurization of FCC gasoline over self-sulfidation adsorbent