In Situ Structure Refactoring of Bismuth Nanoflowers for Highly Selective Electrochemical Reduction of CO2 to Formate

The electrocatalytic CO₂ reduction reaction (CO₂RR) has been considered a promising route toward carbon neutrality and renewable energy conversion. At present, most bismuth (Bi) based electrocatalysts are adopted to reduce CO₂ to formate (HCOOH). However, the mechanism of different Bi nanostructures on the electrocatalytic performance requires more detailed exposition. Herein, a combined chemical replacement and electrochemical reduction process is reported to realize in situ morphology reconstruction from Bi@Bi₂O₃ nanodendrites (Bi@Bi₂O₃-NDs) to Bi nanoflowers (Bi-NFs). The Bi@Bi₂O₃-NDs are proven to undergo a two-step transformation process to form Bi-NFs, aided by Bi₂O₂CO₃ as the intermediate in KHCO₃ solution. Extensive surface reconstruction of Bi@Bi₂O₃-NDs renders the realization of tailored Bi-NFs electrocatalyst that maximize the number of exposed active sites and active component (Bi⁰), which is conducive to the adsorption and activation of CO₂ and accelerated electron transfer process. The as-prepared Bi-NFs exhibit a Faradaic efficiency (FE_formate) of 92.3% at −0.9 V versus RHE and a high partial current density of 28.5 mA cm⁻² at −1.05 V versus RHE for the electroreduction of CO₂ to HCOOH. Moreover, the reaction mechanism is comprehensively investigated by in situ Raman analysis, which confirms that *OCHO is a key intermediate for the formation of HCOOH.     

Multifunctional Mo–N/C@MoS2 Electrocatalysts for HER,OER, ORR,and Zn–Air Batteries

Replacement of noble‐metal platinum catalysts with cheaper, operationally stable, and highly efficient electrocatalysts holds huge potential for large‐scale implementation of clean energy devices. Metal–organic frameworks (MOFs) and metal dichalcogenides (MDs) offer rich platforms for design of highly active electrocatalysts owing to their flexibility, ultrahigh surface area, hierarchical pore structures, and high catalytic activity. Herein, an advanced electrocatalyst based on a vertically aligned MoS₂ nanosheet encapsulated Mo–N/C framework with interfacial Mo–N coupling centers is reported. The hybrid structure exhibits robust multifunctional electrocatalytic activity and stability toward the hydrogen evolution reaction, oxygen evolution reaction, and oxygen reduction reaction. Interestingly, it further displays high‐performance of Zn–air batteries as a cathode electrocatalyst with a high power density of ≈196.4 mW cm^?2 and a voltaic efficiency of ≈63 % at 5 mA cm^?2, as well as excellent cycling stability even after 48 h at 25 mA cm^?2. Such outstanding electrocatalytic properties stem from the synergistic effect of the distinct chemical composition, the unique three‐phase active sites, and the hierarchical pore framework for fast mass transport. This work is expected to inspire the design of advanced and performance‐oriented MOF/MD hybrid‐based electrocatalysts for wider application in electrochemical energy devices.     

A New Strategy for Accelerating Dynamic Proton Transfer of Electrochemical CO2 Reduction at High Current Densities

Developing single-atom electrocatalysts with high activity and superior selectivity at a wide potential window for CO₂ reduction reaction (CO₂RR) still remains a great challenge. Herein, a porous Ni N C catalyst containing atomically dispersed Ni N₄ sites and nanostructured zirconium oxide (ZrO₂@Ni-NC) synthesized via a post-synthetic coordination coupling carbonization strategy is reported. The as-prepared ZrO₂@Ni-NC exhibits an initial potential of −0.3 V, maximum CO Faradaic efficiency (F.E.) of 98.6% ± 1.3, and a low Tafel slope of 71.7 mV dec⁻¹ in electrochemical CO₂RR. In particular, a wide potential window from −0.7 to −1.4 V with CO F.E. of above 90% on ZrO₂@Ni-NC far exceeds those of recently developed state-of-the-art CO₂RR electrocatalysts based on Ni N moieties anchored carbon. In a flow cell, ZrO₂@Ni-NC delivers a current density of 200 mA cm⁻² with a superior CO selectivity of 96.8% at −1.58 V in a practical scale. A series of designed experiments and structural analyses identify that the isolated Ni N₄ species act as real active sites to drive the CO₂RR reaction and that the nanostructured ZrO₂ largely accelerates the protonation process of *CO₂⁻ to *COOH intermediate, thus significantly reducing the energy barrier of this rate-determining step and boosting whole catalytic performance.     

Fine AgPd Nanoalloys Achieving Size and Ensemble Synergy for High-Efficiency CO2 to CO Electroreduction

Alloying the active metal with a second metal is an effective way to tailor the adsorption of reaction intermediates through an ensemble effect. Herein, based on theoretical calculations validating that the ensemble sites composed of Ag and Pd atoms could reduce the energy gap for *COOH and *CO intermediates generated during electrocatalytic CO₂ reduction reaction (eCO₂RR) by either weakening the CO adsorption or enhancing the COOH adsorption, a strategy to produce AgPd alloy nanoparticles with fine sizes for synergizing the ensemble effect and size leverage toward high CO faradaic efficiency in eCO₂RR is reported. In particular, the AgPd alloy nanoparticles at an optimized Ag/Pd atomic ratio of 35/65 affords a maximum CO faradaic efficiency of 98.9% and a CO partial current density of 5.1 mA cm⁻² at the potential of −0.8 V (vs RHE) with satisfactory durability of up to 25 h, outperforming those of most Pd-based electrocatalysts recently reported and demonstrating great potential for further application in producing CO via eCO₂RR at ambient conditions.     

Recent Advances in Atomic‐Level Engineering of Nanostructured Catalysts for Electrochemical CO2 Reduction

Electrochemical reduction of CO₂ into value‐added chemicals provides a promising approach to mitigate climate change caused by CO₂ from excess consumption of fossil fuels. As the CO₂ molecule is chemically inert and the reaction kinetics is sluggish, efficient electrocatalysts are thus highly required for promoting the conversion of CO₂. With great efforts devoted to improving the catalytic performance, the development of electrocatalysts for CO₂ reduction has gone from bulk metals with poor control to nanostructures with atomic precision. Nanostructured electrocatalysts with atomic precision are believed to be capable of combining the advantages of heterogeneous and homogenous catalysts. In this review, the recent advances in designing nanostructured electrocatalysts at the atomic level for boosting the catalytic performance toward CO₂ reduction and revealing the structure–property relationship are summarized. The challenges and opportunities in the near future are also proposed for paving the development of electrocatalytic CO₂ reduction.     

Fe?N4O?C Nanoplates Covalently Bonding on Graphene for Efficient CO2 Electroreduction and Zn?CO2 Batteries (Adv. Funct. Mater. 27/2023)

Electrochemical carbon dioxide (CO₂) reduction into value-added products holds great promise in moving toward carbon neutrality but remains a grand challenge due to lack of efficient electrocatalysts. Herein, the nucleophilic substitution reaction is elaborately harnessed to synthesize carbon nanoplates with a Fe N₄O configuration anchored onto graphene substrate (Fe N₄O C/Gr) through covalent linkages. Density functional theory calculations demonstrate the unique configuration of Fe N₄O with one oxygen (O) atom in the axial direction not only suppresses the competing hydrogen evolution reaction, but also facilitates the desorption of *CO intermediate compared with the commonly planar single-atomic Fe sites. The Fe N₄O C/Gr shows excellent performance in the electroreduction of CO₂ into carbon monoxide (CO) with an impressive Faradaic efficiency of 98.3% at −0.7 V versus reversible hydrogen electrode (RHE) and a high turnover frequency of 3511 h⁻¹. Furthermore, as a cathode catalyst in an aqueous zinc (Zn)-CO₂ battery, the Fe N₄O C/Gr achieves a high CO Faradaic efficiency (≈91%) at a discharge current density of 3 mA cm⁻² and long-term stability over 74 h. This work opens up a new route to simultaneously modulate the geometric and electronic structure of single-atomic catalysts toward efficient CO₂ conversion.     

Cobalt−Iron Oxide Nanosheets for High‐Efficiency Solar‐Driven CO2−H2O Coupling Electrocatalytic Reactions

Solar‐driven electrochemical overall CO₂ splitting (OCO₂S) offers a promising route to store sustainable energy; however, its extensive implementation is hindered by the sluggish kinetics of two key reactions (i.e., CO₂ reduction reaction and oxygen evolution reaction (CO₂RR and OER, respectively)). Here, as dual‐functional catalysts, Co₂FeO₄ nanosheet arrays having high electrocatalytic activities toward CO₂RR and OER are developed. When the catalyst is applied to a complete OCO₂S system driven by a triple junction GaInP₂/GaAs/Ge photovoltaic cell, it shows a high photocurrent density of ≈13.1 mA cm^?2, corresponding to a remarkably high solar‐to‐CO efficiency of 15.5%. Density functional theory studies suggest that the Co sites in Co₂FeO₄ are favorable to the formation of *COOH and *O intermediates and thus account for its efficient bifunctional activities. The results will facilitate future studies for designing highly effective electrocatalysts and devices for OCO₂S.     

Recent Progress of Vacancy Engineering for Electrochemical Energy Conversion Related Applications

Efficient electrocatalysts are key requirements for the development of ecofriendly electrochemical energy-related technologies and devices. It is widely recognized that the introduction of vacancies is becoming an important and valid strategy to promote the electrocatalytic performances of the designed nanomaterials. In this review, the significance of vacancies (i.e., cationic vacancies, anionic vacancies, and mixed vacancies) on the improvement of electrocatalytic performances via three main functionalities, including tuning the electronic structure, regulating the active sites, and improving electrical conductivity, is systematically discussed. Recent achievements in vacancy engineering on various hotspot electrocatalytic processes are comprehensively summarized, with focus on the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), nitrogen reduction reaction (NRR), CO₂ reduction reaction (CO₂RR), and their further applications in overall water-splitting and zinc–air battery devices. The recent development of vacancy engineering for other energy-related applications is also summarized. Finally, the challenges and prospects of vacancy engineering to regulate the electrocatalytic performances of different electrochemical reactions are discussed.     

Facet Dopant Regulation of Cu2O Boosts Electrocatalytic CO2 Reduction to Formate

Electrochemical carbon dioxide reduction reaction (CO₂RR) using clean electric energy provides a sustainable route to generate highly-valuable chemicals and fuels, which is beneficial for realizing the carbon-neutral cycle. Up to now, achieving a narrow product distribution and highly targeted product selectivity over Cu-based electrocatalysts is still a big challenge. Herein, sulfur modification on different crystal planes of cuprous oxide (Cu₂O) is demonstrated, results in an improvement for formate generation to different degrees. Experimental results and density functional theory (DFT) calculations reveal that sulfur species modified on the surface of Cu₂O (100) facet effectively lower the formation energy of key intermediate *OCOH for formate generation compared with Cu₂O (111) facet. As a consequence, the modification of p-Block elements over Cu-based electrocatalysts is an effective strategy to optimize the adsorption energy of key intermediate during CO₂RR, leading to a highly selective product.     

Main-Group s-Block Element Lithium Atoms within Carbon Frameworks as High-Active Sites for Electrocatalytic Reduction Reactions

Inspired by the d-band center theory, previous studies mainly focus on transition metals as electrocatalytic active sites. The s-block metals in the periodic table, especially group ΙA metals with fewer valence electrons, are rarely reported as high-activity electrocatalysts for reduction reactions due to the difficulties associated with their electronic structure regulation. Herein, theoretical calculations demonstrate that group ΙA element lithium (Li) embedded in N, O-doped graphene is an effective electrocatalytic active center for carbon dioxide reduction reaction (CO₂RR) and oxygen reduction reaction (ORR). This catalytic feasibility results from the s–p orbital hybridization between originally empty 2p orbital of Li and the orbitals of coordinated atoms. This vacant 2p orbital can serve as a site for additional p–π conjugation between Li and N, O-doped graphene. Theoretically, the zigzag-type Li–O₂ model shows remarkable CO₂RR activity, while Li–pyridinic–N₁-C₁ exhibits high ORR activity. Furthermore, a carbon-based catalyst with well-anchored Li atoms coordinated to N, O substituents is experimentally demonstrated to exhibit exceptional CO₂RR activity (FE_CO = 98.8% at −0.55 V) and ORR performance in acidic media (E_1/2 = 0.77 V). This is the first report on bifunctional high-performance electrocatalyst utilizing a group ΙA element with performance comparable to that of most previously reported transition-metal-based catalysts.     

Monoclinic Scheelite Bismuth Vanadate Derived Bismuthene Nanosheets with Rapid Kinetics for Electrochemically Reducing Carbon Dioxide to Formate

Electrochemical reduction of CO₂ to high-value chemical feedstocks, such as formate, is one of the most promising ways to alleviate the greenhouse effect. Unfortunately, the exploration of electrocatalysts with high activity and selectivity over a wide potential window (especially low potential for high current density) still remains a grand challenge. In this study, the fabrication of bismuthene nanosheets using an in-situ electrochemical transformation strategy of monoclinic scheelite BiVO₄ flakes is demonstrated. Catalyzing the CO₂ electroreduction in 1 m KHCO₃ aqueous solution, the bismuthene nanosheets exhibit a dramatically high formate Faradaic efficiency (FE) of ≈97.4% and a very large current density of −105.4 mA cm⁻² at −1.0 V versus reversible hydrogen electrode. Significantly, over a record wide potential window of 750 mV from the initial −0.65 V to the applied minimum −1.4 V, the formate FEs of the bismuthene nanosheets are always higher than 90%, outperforming state-of-the-art electrocatalysts. Both experimental and theoretical investigations reveal that, in comparison with ^•COOH and H^• intermediates, the bismuthene nanosheets preferentially promote fast reaction kinetics towards HCOO^•, which eventually accelerates the production of formate.     

Solar-Driven Interfacial Evaporation Accelerated Electrocatalytic Water Splitting on 2D Perovskite Oxide/MXene Heterostructure

The rational design of economic and high-performance electrocatalytic water-splitting systems is of great significance for energy and environmental sustainability. Developing a sustainable energy conversion-assisted electrocatalytic process provides a promising novel approach to effectively boost its performance. Herein, a self-sustained water-splitting system originated from the heterostructure of perovskite oxide with 2D Ti₃C₂T_x MXene on Ni foam (La_1-xSr_xCoO₃/Ti₃C₂T_x MXene/Ni) that shows high activity for solar-powered water evaporation and simultaneous electrocatalytic water splitting is presented. The all-in-one interfacial electrocatalyst exhibits highly improved oxygen evolution reaction (OER) performance with a low overpotential of 279 mV at 10 mA cm⁻² and a small Tafel slope of 74.3 mV dec⁻¹, superior to previously reported perovskite oxide-based electrocatalysts. Density functional theory calculations reveal that the integration of La_0.9Sr_0.1CoO₃ with Ti₃C₂T_x MXene can lower the energy barrier for the electron transfer and decrease the OER overpotential, while COMSOL simulations unveil that interfacial solar evaporation could induce OH⁻ enrichment near the catalyst surfaces and enhance the convection flow above the catalysts to remove the generated gas, remarkably accelerating the kinetics of electrocatalytic water splitting.     

Regulating the Electronic Structure of CoP Nanosheets by O Incorporation for High‐Efficiency Electrochemical Overall Water Splitting

The exploration of earth‐abundant and high‐efficiency bifunctional electrocatalysts for overall water splitting is of vital importance for the future of the hydrogen economy. Regulation of electronic structure through heteroatom doping represents one of the most powerful strategies to boost the electrocatalytic performance of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, a rational design of O‐incorporated CoP (denoted as O‐CoP) nanosheets, which synergistically integrate the favorable thermodynamics through modification of electronic structures with accelerated kinetics through nanostructuring, is reported. Experimental results and density functional theory simulations manifest that the appropriate O incorporation into CoP can dramatically modulate the electronic structure of CoP and alter the adsorption free energies of reaction intermediates, thus promoting the HER and OER activities. Specifically, the optimized O‐CoP nanosheets exhibit efficient bifunctional performance in alkaline electrolyte, requiring overpotentials of 98 and 310 mV to deliver a current density of 10 mA cm^?2 for HER and OER, respectively. When served as bifunctional electrocatalysts for overall water splitting, a low cell voltage of 1.60 V is needed for achieving a current density of 10 mA cm^?2. This proposed anion‐doping strategy will bring new inspiration to boost the electrocatalytic performance of transition metal–based electrocatalysts for energy conversion applications.     

Cu/Cu2O Interconnected Porous Aerogel Catalyst for Highly Productive Electrosynthesis of Ethanol from CO2

Use of Cu and Cu⁺ is one of the most promising approaches for the production of C₂ products by the electrocatalytic CO₂ reduction reaction (CO₂RR) because it can facilitate CO₂ activation and C C dimerization. However, the selective electrosynthesis of C₂₊ products on Cu⁰ Cu⁺ interfaces is critically limited due to the low electrocatalytic production of ethanol relative to ethylene. In this study, a novel porous Cu/Cu₂O aerogel network is introduced to afford high ethanol productivity by the electrocatalytic CO₂RR. The aerogel is synthesized by a simple chemical redox reaction of a precursor and a reducing agent. CO₂RR results reveal that the Cu/Cu₂O aerogel produces ethanol as the major product, exhibiting a Faradaic efficiency (FE_EtOH) of 41.2% and a partial current density (J_EtOH) of 32.55 mA cm⁻² in an H-cell reactor. This is the best electrosynthesis performance for ethanol production reported thus far. Electron microscopy and electrochemical analysis results reveal that this dramatic increase in the electrosynthesis performance for ethanol can be attributed to a large number of Cu⁰ Cu⁺ interfaces and an increase of the local pH in the confined porous aerogel network structure with a high-surface-area.     

Hierarchical Ni/N/C Single-Site Catalyst Achieving Industrial-Level Current Density and Ultra-Wide Potential Plateau of High CO Faradic Efficiency for CO2 Electroreduction

The practical applications of CO₂ electroreduction to CO driven by renewable electricity should simultaneously meet the requests of industrial-level CO partial current density (J_CO) at least 100 mA cm⁻², wide potential window of high CO faradic efficiency (FE_CO), and low cost. Herein, a new strategy is reported to construct porous hierarchical Ni/N/C single-site catalyst with excellent catalytic activity via coating Ni-containing ZIF-8 on mesostructured basic magnesium carbonate template followed by pyrolysis. The abundant micropores facilitate the formation of numerous edge-hosted Ni-N₄ sites with high intrinsic activity, and the interconnected macro/mesopores much promote CO₂ delivery and CO release for the full expression of intrinsic activity. Consequently, the catalyst exhibits the industrial-level J_CO of 105–462 mA cm⁻² at the potential range of −0.6∼−1.3 V with ultra-wide high FE_CO plateau (>90%@−0.4∼−1.3 V), showing great promise for practical application. This study provides a general synthetic strategy to explore high-performance hierarchical M/N/C electrocatalysts.     

Dual-Engineering of Porous Structure and Carbon Edge Enables Highly Selective H2O2 Electrosynthesis

Edge engineering has emerged as a powerful strategy to activate inert carbon surfaces, and thus achieve a notable enhanced electrocatalytic activity. However, the rational manipulation of carbon edges to achieve enhanced catalytic performance remains a formidable challenge, primarily hindered by immature synthesis methods and the obscured understanding of the structure-activity relationship. Herein, an organic–inorganic hybrid co-assembly strategy is used to fabricate a series of mesoporous carbon nanofibers (MCNFs) with controllable edge site densities and the impact of edge population on electrochemical oxygen reduction reaction (ORR) pathways is investigated. The optimized MCNFs catalyst exhibits a remarkable 2e⁻ ORR performance, as evidenced by a high H₂O₂ selectivity (>90%) across a wide potential window of 0.6 V and a large cathodic current density of −3.0 mA cm⁻² (at 0.2 V vs. reversible hydrogen electrode). Strikingly, the density of carbon edge sites can be changed to tune the ORR activity and selectivity. Experimental validation and density functional theory calculations confirm that the presence of edge defects can optimize the adsorption strength of *OOH intermediates and balance the selectivity and activity of the 2e⁻ ORR process. This study provides a new path to achieve high ORR activity and 2e⁻ selectivity in carbon-based electrocatalysts.     

Engineering Silver-Enriched Copper Core-Shell Electrocatalysts to Enhance the Production of Ethylene and C2+ Chemicals from Carbon Dioxide at Low Cell Potentials

Copper catalysts are widely studied for the electroreduction of carbon dioxide (CO₂) to value-added hydrocarbon products. Controlling the surface composition of copper nanomaterials may provide the electronic and structural properties necessary for carbon-carbon coupling, thus increasing the Faradaic efficiency (FE) towards ethylene and other multi-carbon (C₂₊) products. Synthesis and catalytic study of silver-coated copper nanoparticles (Cu@Ag NPs) for the reduction of CO₂ are presented. Bimetallic CuAg NPs are typically difficult to produce due to the bulk immiscibility between these two metals. Slow injection of the silver precursor, concentrations of organic capping agents, and gas environment proved critical to control the size and metal distribution of the Cu@Ag NPs. The optimized Cu@Ag electrocatalyst exhibited a very low onset cell potential of −2.25 V for ethylene formation, reaching a FE towards C₂₊ products (FE_C2+) of 43% at −2.50 V, which is 1.0 V lower than a reference Cu catalyst to reach a similar FE_C2+. The high ethylene formation at low potentials is attributed to enhanced C C coupling on the Ag enriched shell of the Cu@Ag electrocatalysts. This study offers a new catalyst design towards increasing the efficiency for the electroreduction of CO₂ to value-added chemicals.     

MnO Enabling Highly Efficient and Stable Co-Nx/C for Oxygen Reduction Reaction in both Acidic and Alkaline Media

In situ growing transition metals on N-doped carbon by atomic doping produces a class of promising alternatives to replace Pt-based catalysts for redox reactions, yet still suffer from unsatisfactory activity and durability in acidic and basic media. Herein, a simple synthetic strategy to fabricate an MnO modifying Co-N_x/C catalyst with high activity and robust durability is presented. The interphase engineering well controls the Co and N species in the carbon matrix, affording the material with more pyridine N and graphite N; the interaction between Co-N_x and MnO phase is also well discussed. Accordingly, the obtained Co-N_x/C-MnO catalyst exhibits excellent electrocatalytic properties towards oxygen reduction reaction, achieving a half-wave potential of 0.87 and 0.66 V versus reversible hydrogen electrode in 0.1 m KOH and 0.1 m HClO₄ solutions, as well as excellent durability with only −16.9 and −12.2 mV shift after 1000 cycles, respectively. This study provides insights into the design of noble-metal-free electrocatalysts from the perspective of active sites and catalyst carriers.     

La2O3‐Modified LaTiO2N Photocatalyst with Spatially Separated Active Sites Achieving Enhanced CO2 Reduction

Activating CO₂ molecule and promoting proton release from kinetically sluggish water oxidation are two important half‐reaction processes for achieving efficient solar‐driven conversion of CO₂ to fuels. Here, an effective route is proposed that uses a solid base to modify photocatalyst with defects, aiming to simultaneously accelerate the two reaction processes. To verify this hypothesis, the La₂O₃ is decorated on surface of LaTiO₂N with oxygen vacancies, achieving a twofold increase in CH₄ yield rate for CO₂ reduction. The prominent activity results from the following two effects: (1) The O^2? in La₂O₃ as basic sites favors CO₂ chemisorption in the form of CO₃^2? species, greatly contributing to both the bending of O? C? O bond and the decrease of the lowest unoccupied molecule orbit energy of CO₂ molecule. (2) The oxygen vacancies on LaTiO₂N are beneficial in activating H₂O to adsorbed OH, thus effectively decreasing the reaction barriers of water oxidation to release protons. The design concept of simultaneously activating the CO₂ and H₂O at different spatial sites may offer a new strategy to suppress the reverse reactions for efficient solar energy conversion.     

High‐Performance Overall CO2 Splitting on Hierarchical Structured Cobalt Disulfide with Partially Removed Sulfur Edges

The ability to develop bifunctional electrocatalysts for concurrent CO₂ reduction reaction (CO₂RR) and oxygen evolution reaction (OER) is the key to the practical application of CO₂ splitting to produce CO. However, this remains a grand challenge. Herein, a robust strategy to rationally craft hierarchical structured bifunctional electrocatalysts composed of 3D CoS₂ nanocages interconnected on 2D CoS₂ nanosheet arrays (denoted hierarchical CoS₂ nanocages) for high‐performance CO₂ splitting is developed. The subsequent calcination removes the partial S edges of CoS₂, thereby strongly suppressing the hydrogen evolution reaction (HER) of CoS₂. By combining theoretic and experimental results, for the first time, it is discovered that the plane S of CoS₂, instead of S edges, are highly active for CO₂RR but inactive for HER, rendering the plane S as ideal active sites for CO₂RR. Intriguingly, the composition tuning via calcination and the presence of a hierarchical architecture confer hierarchical CoS₂ nanocages respective outstanding CO₂RR and OER performance. Notably, the hierarchical CoS₂ nanocages can be exploited as bifunctional electrocatalysts for overall CO₂ splitting to yield the current density of 1 mA cm^?2 at a small cell voltage of 1.92 V, much lower than the widely reported values (>2.5 V).