Iron–nitrogen (Fe–N) sites confined within carbon are highly active to catalyze the oxygen reduction reaction (ORR). The mesoporous structure of carbon facilitates the mass transport and availability to the Fe–N sites during the ORR; however, the construction of mesoporous carbon architecture with highly exposed and accessible Fe–N active sites remains challenging. Herein, 3D-to-2D transformation of zeolitic imidazolate framework-7 (ZIF-7) was successfully achieved via convenient impregnation in ammonium ferric citrate aqueous solution. After pyrolysis, isolated Fe–N sites are generated and confined within highly mesoporous carbon without using any additional modulator or template. The optimal Fe–N catalyst exhibits excellent performance toward ORR in alkaline medium, exceeding commercial 40% Pt/C catalyst in terms of activity, stability, and methanol resistance.Keywords: 3D-to-2D transformation; iron−nitrogen sites; oxygen reduction reaction; self-assembly; zeolitic imidazolate framework-7;

The electrochemical CO2 reduction reaction (CO2RR) typically uses transition metals as the catalysts. To improve the efficiency, tremendous efforts have been dedicated to tuning the morphology, size, and structure of metal catalysts and employing electrolytes that enhance the adsorption of CO2. We report here a strategy to enhance CO2RR by constructing the metal–oxide interface. We demonstrate that Au–CeOx shows much higher activity and Faradaic efficiency than Au or CeOx alone for CO2RR. In situ scanning tunneling microscopy and synchrotron-radiation photoemission spectroscopy show that the Au–CeOx interface is dominant in enhancing CO2 adsorption and activation, which can be further promoted by the presence of hydroxyl groups. Density functional theory calculations indicate that the Au–CeOx interface is the active site for CO2 activation and the reduction to CO, where the synergy between Au and CeOx promotes the stability of key carboxyl intermediate (*COOH) and thus facilitates CO2RR. Similar interface-enhanced CO2RR is further observed on Ag–CeOx, demonstrating the generality of the strategy for enhancing CO2RR.

Silver (Ag) is one of the widely investigated catalysts for CO2 electroreduction. To improve the faradaic efficiency for CO production over Ag catalysts, many efforts have been devoted to tuning the size and morphology of Ag catalysts, using Ag-containing complex compounds or ionic liquid electrolyte. Herein, we report a strategy to enhance CO2 electroreduction by constructing a Ag2O/layered zeolitic imidazolate framework (ZIF) composite structure via one-pot hydrothermal treatment of ZIF-7 nanoparticles (NPs) in AgNO3 aqueous solution. The Ag2O/layered ZIF shows much higher CO faradaic efficiency and current density than the layered ZIF or Ag/C alone. The performance improvement in CO2 electroreduction over the Ag2O/layered ZIF is probably attributed to the synergistic effect between Ag2O NPs and the layered ZIF, as well as facilitated mass transport due to the high specific surface area of the Ag2O/layered ZIF.

Correction for ‘Electrochemical promotion of catalysis over Pd nanoparticles for CO2 reduction’ by Fan Cai et al., Chem. Sci., 2017, DOI: 10.1039/c6sc04966d.

Active-phase engineering is regularly utilized to tune the selectivity of metal nanoparticles (NPs) in heterogeneous catalysis. However, the lack of understanding of the active phase in electrocatalysis has hampered the development of efficient catalysts for CO2 electroreduction. Herein, we report the systematic engineering of active phases of Pd NPs, which are exploited to select reaction pathways for CO2 electroreduction. In situ X-ray absorption spectroscopy, in situ attenuated total reflection-infrared spectroscopy, and density functional theory calculations suggest that the formation of a hydrogen-adsorbed Pd surface on a mixture of the α- and β-phases of a palladium-hydride core (α+β PdHx@PdHx) above −0.2 V (vs. a reversible hydrogen electrode) facilitates formate production via the HCOO* intermediate, whereas the formation of a metallic Pd surface on the β-phase Pd hydride core (β PdHx@Pd) below −0.5 V promotes CO production via the COOH* intermediate. The main product, which is either formate or CO, can be selectively produced with high Faradaic efficiencies (>90%) and mass activities in the potential window of 0.05 to −0.9 V with scalable application demonstration.

Zeolitic imidazolate frameworks (ZIFs) are widely employed in catalyst synthesis as parental materials for electrochemical energy storage and conversion. Herein, we have demonstrated a facile synthesis of highly efficient catalyst for oxygen reduction reaction in both alkaline and acidic medium, which is derived from ZIF-8 functionalized with ammonium ferric citrate via two-step pyrolysis in Ar and NH3 atmosphere. The results reveal that the catalytic activity improvement after NH3 pyrolysis benefits from mesopore-dominated morphology and high utilization of Fe-containing active sites. The optimum catalyst shows excellent performance in zinc-air battery and polymer electrolyte membrane fuel cell tests.ZIF-8 derived carbon material via two-step pyrolysis in Ar and NH3 atmosphere, demonstrates excellent performance towards oxygen reduction reaction in both alkaline and acidic medium, which also shows superior activities in polymer electrolyte membrane fuel cell and zinc-air battery tests. Download high-res image (146KB)Download full-size image

Co-electrolysis of CO2 and H2O using high-temperature solid oxide electrolysis cells (SOECs) into valuable chemicals has attracted great attentions recently due to the high conversion and energy efficiency, which provides opportunities of reducing CO2 emission, mitigating global warming and storing intermittent renewable energies. A single SOEC typically consists of an ion conducting electrolyte, an anode and a cathode where the co-electrolysis reaction takes place. The high operating temperature and difficult activated carbon–oxygen double-bond of CO2 put forward strict requirements for SOEC cathode. Great efforts are being devoted to develop suitable cathode materials with high catalytic activity and excellent long-term stability for CO2/H2O electro-reduction. The so far cathode material development is the key point of this review and alternative strategies of high-performance cathode material preparation is proposed. Understanding the mechanism of CO2/H2O electro-reduction is beneficial to highly active cathode design and optimization. Thus the possible reaction mechanism is also discussed. Especially, a method in combination with electrochemical impedance spectroscopy (EIS) measurement, distribution functions of relaxation times (DRT) calculation, complex nonlinear least square (CNLS) fitting and operando ambient pressure X-ray photoelectron spectroscopy (APXPS) characterization is introduced to correctly disclose the reaction mechanism of CO2/H2O co-electrolysis. Finally, different reaction modes of the CO2/H2O co-electrolysis in SOECs are summarized to offer new strategies to enhance the CO2 conversion. Otherwise, developing SOECs operating at 300–600 °C can integrate the electrochemical reduction and the Fischer–Tropsch reaction to convert the CO2/H2O into more valuable chemicals, which will be a new research direction in the future.Co-electrolysis of CO2 and H2O using high-temperature solid oxide electrolysis cells (SOECs) into valuable chemicals can provide opportunities of reducing CO2 emission, mitigating global warming and storing intermittent renewable energies, which have attracted great attentions recently due to the high conversion and energy efficiency. Download high-res image (212KB)Download full-size image

Nitrogen-doped carbon materials encapsulating 3d transition metals are promising alternatives to replace noble metal Pt catalysts for efficiently catalyzing the oxygen reduction reaction (ORR). Herein, we use cobalt substituted perfluorosulfonic acid/polytetrafluoroethylene copolymer and dicyandiamide as the pyrolysis precursor to synthesize nitrogen-doped carbon nanotube (NCNT) encapsulating cobalt nanoparticles hybrid material. The carbon layers and specific surface area of NCNT have a critical role to the ORR performance due to the exposed active sites, determined by the mass ratio of the two precursors. The optimum hybrid material exhibits high ORR activity and stability, as well as excellent performance and durability in zinc–air battery.High-surface-area and few-layered nitrogen-doped carbon nanotube encapsulating Co nanoparticles showed excellent performance and durability in Zn–air battery.Download high-res image (303KB)Download full-size image

•Surface functionalization of zeolitic imidazolate framework-8 (ZIF-8) is explored.•Ammonium ferric citrate is selectively confined on the surface of ZIF-8.•Highly exposed iron-nitrogen sites within carbon matrix are obtained by pyrolysis.•High mass activity toward oxygen reduction reaction in acidic medium is obtained.•Superior selectivity and mass activity toward CO2 electroreduction is achieved.Isolated metal-nitrogen sites are highly active to catalyze the oxygen and carbon dioxide electroreduction, however, the limited content of isolated metal-nitrogen sites within carbon matrix urgently requires full exposure of the active sites on the surface for efficient catalysis. Herein, post-synthetic modification strategy is explored to selectively confine ammonium ferric citrate on the surface of zeolitic imidazolate framework-8 (ZIF-8) nanoparticles. After pyrolysis, isolated iron-nitrogen sites are generated and located on the carbon matrix surface. The highly exposed iron-nitrogen sites demonstrate excellent mass activity toward oxygen reduction reaction in acidic medium, outperforming most reported non-noble metal catalysts, and also show superior selectivity and mass activity toward carbon dioxide electroreduction compared to most reported noble metal catalysts.Highly exposed iron-nitrogen sites on the carbon matrix surface, generated by surface functionalization of ZIF-8 with ammonium ferric citrate and subsequent pyrolysis, show efficient catalysis towards oxygen and carbon dioxide electroreduction.Download high-res image (452KB)Download full-size image

Electrochemical promotion of catalysis (EPOC) has been shown to accelerate the rate of many heterogeneous catalytic reactions; however, it has rarely been reported in low-temperature aqueous electrochemical reactions. Herein, we report a significant EPOC effect for the CO2 reduction to generate formate over Pd nanoparticles (NPs) in a 1 M KHCO3 aqueous solution. By applying a negative potential over differently-sized Pd NPs, the rate of formate production is greatly improved as compared to that at an open-circuit voltage, with a rate enhancement ratio ranging from 10 to 143. The thermocatalytic and electrocatalytic reduction of CO2 compete with each other and are promoted by the applied negative potential and H2 in the feeds, respectively. Inspired by the EPOC effect, a composite electrode containing Pd/C and Pt/C catalysts on different sides of a carbon paper was constructed for catalyzing the CO2 reduction without adding H2 to the feeds. Water electrolysis over Pt NPs generates H2, which then effectively promotes formate production over Pd NPs.

•Nanoporous ZnO was prepared by a hydrothermal method followed by thermal decomposition.•A maximum CO Faradaic efficiency of 92.0% was achieved at − 1.66 V (vs. Ag/AgCl).•The CO Faradaic efficiency is much higher than 55.5% over Zn foil.•In situ X-ray absorption spectroscopy results indicate that nanoporous ZnO was reduced to Zn.•The enhancement is due to increased surface area and more coordination unsaturated surface atoms.Nanoporous zinc oxide (ZnO) is prepared by a hydrothermal method followed by thermal decomposition for electrocatalytic reduction of CO2. In situ X-ray absorption spectroscopy results indicate that ZnO is reduced to Zn under the electrolysis conditions for catalyzing CO2 electroreduction. The reduced nanoporous ZnO exhibits obviously higher CO Faradaic efficiency and current density than commercial Zn foil with a maximum CO Faradaic efficiency of 92.0%, suggesting that the nanoporous structure facilitates electrocatalytic reduction of CO2 over reduced nanoporous ZnO, probably due to increased surface area and more coordination unsaturated surface atoms.

Silicon carbide (SiC) was extracted using CCl4 and NH3 at 800 °C to form a SiC core with a derived nitrogen-doped carbon shell (SiC@N–C), which is explored as a supporting material for iron nanoparticles encapsulated in nitrogen-doped carbon (Fe@N–C) due to its excellent corrosion resistance. The carbon shell around SiC is essential to successfully grow Fe@N–C around SiC@N–C during pyrolysis of cyanamide and iron acetate. In sharp contrast, Fe3Si supported on SiC was obtained using pristine SiC as the supporting material. Fe@N–C/SiC@N–C showed much higher activity for oxygen reduction reaction than SiC@N–C and Fe3Si/SiC, even exceeding that of a commercial Pt/C catalyst in alkaline medium. Furthermore, Fe@N–C/SiC@N–C also demonstrated higher durability and methanol resistance than the Pt/C catalyst.

•High selectivity for CO production can be achieved with PdCu alloy nanoparticles.•Controllable size and composition are critical to the catalytic activity enhancement.•Pd85Cu15/C shows highest Faradaic efficiency, current density and mass activity for CO.Selective and efficient conversion of carbon dioxide (CO2) to a reusable form of carbon via the electrochemical reduction of CO2 has attracted much attention recently, as it is a promising approach for the storage of renewable energy. Herein, we synthesize palladium-copper bimetallic nanoparticles with different compositions, which serve as a well-defined platform to understand their fundamental catalytic activity in CO2 reduction. Among PdCu/C and Pd/C catalysts tested, Pd85Cu15/C catalyst shows the highest CO Faradaic efficiency of 86%, CO current density of 6.9 mA cm−2 and mass activity for CO production of 24.5 A g−1 at −0.89 V vs. RHE in CO2-saturated 0.1 M KHCO3 solution, which is about 5 times, 8 times and 2.2 times higher than Pd/C catalyst, respectively. It was suggested from EXAFS and CO TPD-MS studies that the highly selective CO production on Pd85Cu15/C catalyst is due to the presence of an optimum ratio of the copper element and low-coordination sites over monometallic Pd active for H2 evolution with low overpotential. We believe that controllable size and composition for the bimetallic nanoparticles are critical to the CO2 reduction activity enhancement and high CO Faradaic efficiency. The insights gained through this work may shed light in a foundation for designing efficient catalysts for electrochemical reduction of CO2.The bimetallic palladium-copper nanoparticles with different compositions were loaded on the carbon support to obtain bimetallic PdCu/C catalysts towards CO2 electrochemical reduction. Among PdCu/C and Pd/C catalysts tested, Pd85Cu15/C catalyst shows the highest CO Faradaic efficiency of 86%, CO current density of 6.9 mA cm−2 and mass activity for CO production of 24.5 A g−1 at −0.89 V vs. RHE in CO2-saturated 0.1 M KHCO3 solution, which is about 5 times, 8 times and 2.2 times higher than Pd/C catalyst, respectively.

Size effect has been regularly utilized to tune the catalytic activity and selectivity of metal nanoparticles (NPs). Yet, there is a lack of understanding of the size effect in the electrocatalytic reduction of CO2, an important reaction that couples with intermittent renewable energy storage and carbon cycle utilization. We report here a prominent size-dependent activity/selectivity in the electrocatalytic reduction of CO2 over differently sized Pd NPs, ranging from 2.4 to 10.3 nm. The Faradaic efficiency for CO production varies from 5.8% at −0.89 V (vs reversible hydrogen electrode) over 10.3 nm NPs to 91.2% over 3.7 nm NPs, along with an 18.4-fold increase in current density. Based on the Gibbs free energy diagrams from density functional theory calculations, the adsorption of CO2 and the formation of key reaction intermediate COOH* are much easier on edge and corner sites than on terrace sites of Pd NPs. In contrast, the formation of H* for competitive hydrogen evolution reaction is similar on all three sites. A volcano-like curve of the turnover frequency for CO production within the size range suggests that CO2 adsorption, COOH* formation, and CO* removal during CO2 reduction can be tuned by varying the size of Pd NPs due to the changing ratio of corner, edge, and terrace sites.

•Significant pH dependence toward CO2 reduction was observed over Pd nanoparticles.•CO Faradaic efficiency over Pd nanoparticles varied from 3.2% to 93.2% in a narrow pH range from 1.5 to 4.2.•Pt nanoparticles completely contributed to hydrogen evolution reaction in the pH range.•Increased hydrogen binding energy at high pH suppressed hydrogen evolution reaction over Pd and Pt nanoparticles.•Lowered adsorption affinity of CO-like intermediate on Pd compared to Pt accounted for their different pH sensitivity.Adsorbed hydrogen participates in electrocatalytic reduction of CO2 and competitive hydrogen evolution reaction (HER) simultaneously, and its reaction pathway greatly affects the activity and selectivity of CO2 reduction. In this work, we investigate pH effect on electrocatalytic reduction of CO2 over Pd and Pt nanoparticles (NPs) with a similar size in a pH range from 1.5 to 4.2. Pt NPs completely contribute to HER in the pH range. Over Pd NPs, Faradaic efficiency for CO production at − 1.19 V (vs. reversible hydrogen electrode) varies from 3.2% at pH of 1.5 to 93.2% at pH of 4.2, and current density for CO production reaches maximum at pH of 2.2. The significant enhancement of Faradaic efficiency and current density for CO production over Pd NPs at high pH values is attributed to decreased kinetics of hydrogen evolution reaction by increasing hydrogen binding energy and lowered adsorption affinity of CO-like intermediate compared to Pt.

•High-density carbon-encapsulated iron nanoparticles are successfully obtained.•Dicyandiamide and ammonium ferric citrate are used as pyrolysis precursors.•Iron surface area and nitrogen content in the material can be tuned conveniently.•The material demonstrates excellent bifunctionality for oxygen electrolysis.•The material shows high performance and cycling durability in zinc-air battery.Exploring highly efficient electrocatalysts toward oxygen reduction and evolution reactions are critical for the development of rechargeable zinc–air batteries. As a novel class of electrocatalyst, transition metal nanoparticles encapsulated within nitrogen-doped carbon have been regarded as competitive alternative to replace noble metal electrocatalysts. Herein, we report successful synthesis of high-density iron nanoparticles encapsulated within nitrogen-doped carbon nanoshell (Fe@N–C) by solid-phase precursor׳s pyrolysis of dicyandiamide and ammonium ferric citrate. The resulting Fe@N–C material shows excellent bifunctionality for ORR and OER in alkaline medium compared to state-of-the-art commercial Pt/C and IrO2, which demonstrates high performance and cycling durability in zinc–air battery as efficient oxygen electrocatalyst.High-density iron nanoparticles encapsulated within nitrogen-doped carbon nanoshell demonstrates excellent bifunctionality for oxygen reduction and evolution reactions in alkaline medium, showing high performance and cycling durability in zinc–air battery as efficient oxygen electrocatalyst.

The hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are important electrocatalytic processes in water electrolyzers. Identifying efficient non-precious metal catalysts for HER and OER remains a great challenge for applications in different kinds of electrolyzers. Herein, we report that cobalt nanoparticles encapsulated in nitrogen-doped carbon (Co@N–C) show high activity and durability for HER in a wide pH range and for OER in alkaline medium as a bifunctional catalyst. The HER and OER activities of Co@N–C are higher than those of multiwall carbon nanotube and iron nanoparticles encapsulated in nitrogen-doped carbon with a similar content of nitrogen. Electrolyzer prototypes using Nafion NRE-212 as electrolyte membrane and Co@N–C as cathode or anode catalyst are constructed, showing potential practical applications in water splitting.

Ammonium ferric citrate (AFC) was used as a single-source molecular precursor to prepare Fe/Fe3C nanoparticles encapsulated in nitrogen-doped carbon by pyrolysis in Ar atmosphere followed by acid-leaching. Comparative studies, using citric acid and ferric citrate as the precursors, indicated that the ammonia and ferric ion in AFC and the pyrolysis temperature affected the composition of iron species and the properties of carbon in AFC-derived materials. Above the pyrolysis temperature of 600 °C, the iron species were Fe/Fe3C, and the carbon had a hollow graphitic nanoshell structure in AFC-derived materials. The specific surface area and content of nitrogen element decreased with increasing pyrolysis temperature. The AFC-derived material pyrolyzed at 600 °C had the optimal graphitization degree, specific surface area (489 m2 g−1) and content of nitrogen (1.8 wt.%), thus resulted in the greatest activity for oxygen reduction reaction among the AFC-derived materials pyrolyzed at different temperatures. The AFC-derived material pyrolyzed at 600 °C exhibited improved methanol-resistance ability compared with Pt/C catalyst.

A PtFe/C catalyst has been synthesized by impregnation and high-temperature reduction followed by acid-leaching. X-ray diffraction, X-ray photoelectron spectroscopy and X-ray atomic near edge spectroscopy characterization reveal that Pt3Fe alloy formation occurs during high-temperature reduction and that unstable Fe species are dissolved into acid solution. The difference in Fe concentration from the core region to the surface and strong O-Fe bonding may drive the outward diffusion of Fe to the highly corrugated Pt-skeleton, and the resulting highly dispersed surface FeOx is stable in acidic medium, leading to the construction of a Pt3Fe@Pt-FeOx architecture. The as prepared PtFe/C catalyst demonstrates a higher activity and comparable durability for the oxygen reduction reaction compared with a Pt/C catalyst, which might be due to the synergetic effect of surface and subsurface Fe species in the PtFe/C catalyst.

Vulcan XC-72R, Ketjen Black EC 300J and Black Pearls 2000 carbon blacks were used as the additive in Pt black cathode catalyst layer to investigate the effect on direct methanol fuel cell (DMFC) performance. The carbon blacks, Pt black catalyst and catalyst inks were characterized by N2 adsorption and scanning transmission electron microscopy (STEM) with Energy dispersive X-ray (EDX) spectroscopy. The cathode catalyst layers without and with carbon black additive were characterized by scanning electron microscopy, EDX, cyclic voltammetry and current-voltage curve measurements. Compared with Vulcan XC-72R and Black Pearls 2000, Ketjen Black EC 300J was more beneficial to increase the electrochemical surface area and DMFC performance of the cathode catalyst layer. The cathode catalyst layer with Ketjen Black EC 300J additive was kept intimately binding with the Nafion membrane after 360 h stability test of air-breathing DMFC.

Replacing platinum for catalyzing hydrogen evolution reaction (HER) in acidic medium remains great challenges. Herein, we prepared few-layered MoS2 by ball milling as an efficient catalyst for HER in acidic medium. The activity of as-prepared MoS2 had a strong dependence on the ball milling time. Furthermore, Ketjen Black EC 300J was added into the ball-milled MoS2 followed by a second ball milling, and the resultant MoS2/carbon black hybrid material showed a much higher HER activity than MoS2 and carbon black alone. The enhanced activity of the MoS2/carbon black hybrid material was attributed to the increased abundance of catalytic edge sites of MoS2 and excellent electrical coupling to the underlying carbon network.MoS2/Ketjen Black EC 300J hybrid material demonstrates high activity for hydrogen evolution reaction due to increased abundance of MoS2 edge sites and excellent electrical coupling to the underlying carbon network.Download high-res image (442KB)Download full-size image

Carbon dioxide transformation to fuels or chemicals provides an attractive approach for its utilization as feedstock and its emission reduction. Herein, we report a gas-phase electrocatalytic reduction of CO2 in an electrolytic cell, constructed using phosphoric acid-doped polybenzimidazole (PBI) membrane, which allowed operation at 170 °C. Pt/C and PtMo/C with variable ratio of Pt/Mo were studied as the cathode catalysts. The results showed that PtMo/C catalysts significantly enhanced CO formation and inhibited CH4 formation compared with Pt/C catalyst. Characterization by X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy revealed that most Mo species existed as MoO3 in PtMo/C catalysts and the interaction between Pt and MoOx was likely responsible for the enhanced CO formation rate although these bicomponent catalysts in general had a larger particle size than Pt/C catalyst.Electrolytic cell based on phosphoric acid-doped PBI (PA-PBI) membrane is developed to explore the gas-phase reduction of CO2 at 170 °C. Addition of Mo species to Pt in PtMo/C catalyst significantly promotes the formation of CO and inhibits the formation of CH4 compared with Pt/C catalyst.Download full-size image

•Pd-Pt/C catalysts with different metal deposition sequences were prepared.•The deposition of Pt prior to Pd showed the highest formate production rate.•The mass activity of the best Pd-Pt/C catalyst was 21.5 times that of Pd/C at − 0.3 V.Pd/C catalysts facilitate CO2 electroreduction to formate with high Faradaic efficiency at low overpotentials. However, they are prone to deactivation due to CO poisoning. In this work, three carbon-supported Pd-Pt catalysts with different metal deposition sequences are prepared and their efficacy towards formate production over the Pd surface is studied. X-ray photoelectron spectroscopy and X-ray absorption spectroscopy results show that the surface composition and coordination number of Pd-Pd in carbon-supported Pd-Pt catalysts are greatly influenced by the order in which Pd and Pt nanoparticles (NPs) are deposited. The deposition of Pt NPs prior to Pd NPs on the carbon support gives the best results for formate production with high Faradaic efficiency.

Electrochemical reduction of CO2 provides a sustainable solution to address the intermittent renewable electricity storage while recycling CO2 to produce fuels and chemicals. Highly efficient catalytic materials and reaction systems are required to drive this process economically. This Review highlights the new trends in advancing the electrochemical reduction of CO2 by developing and designing nanostructured heterogeneous catalysts. The activity, selectivity and reaction mechanism are significantly affected by the nano effects in nanostructured heterogeneous catalysts. In the future, energy efficiency and current density in electrochemical reduction of CO2 need to be further improved to meet the requirements for practical applications.

Silicon carbide (SiC) was extracted using CCl4 and NH3 at 800 °C to form a SiC core with a derived nitrogen-doped carbon shell (SiC@N–C), which is explored as a supporting material for iron nanoparticles encapsulated in nitrogen-doped carbon (Fe@N–C) due to its excellent corrosion resistance. The carbon shell around SiC is essential to successfully grow Fe@N–C around SiC@N–C during pyrolysis of cyanamide and iron acetate. In sharp contrast, Fe3Si supported on SiC was obtained using pristine SiC as the supporting material. Fe@N–C/SiC@N–C showed much higher activity for oxygen reduction reaction than SiC@N–C and Fe3Si/SiC, even exceeding that of a commercial Pt/C catalyst in alkaline medium. Furthermore, Fe@N–C/SiC@N–C also demonstrated higher durability and methanol resistance than the Pt/C catalyst.

The hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are important electrocatalytic processes in water electrolyzers. Identifying efficient non-precious metal catalysts for HER and OER remains a great challenge for applications in different kinds of electrolyzers. Herein, we report that cobalt nanoparticles encapsulated in nitrogen-doped carbon (Co@N–C) show high activity and durability for HER in a wide pH range and for OER in alkaline medium as a bifunctional catalyst. The HER and OER activities of Co@N–C are higher than those of multiwall carbon nanotube and iron nanoparticles encapsulated in nitrogen-doped carbon with a similar content of nitrogen. Electrolyzer prototypes using Nafion NRE-212 as electrolyte membrane and Co@N–C as cathode or anode catalyst are constructed, showing potential practical applications in water splitting.

Correction for ‘Electrochemical promotion of catalysis over Pd nanoparticles for CO2 reduction’ by Fan Cai et al., Chem. Sci., 2017, DOI: 10.1039/c6sc04966d.

Electrochemical promotion of catalysis (EPOC) has been shown to accelerate the rate of many heterogeneous catalytic reactions; however, it has rarely been reported in low-temperature aqueous electrochemical reactions. Herein, we report a significant EPOC effect for the CO2 reduction to generate formate over Pd nanoparticles (NPs) in a 1 M KHCO3 aqueous solution. By applying a negative potential over differently-sized Pd NPs, the rate of formate production is greatly improved as compared to that at an open-circuit voltage, with a rate enhancement ratio ranging from 10 to 143. The thermocatalytic and electrocatalytic reduction of CO2 compete with each other and are promoted by the applied negative potential and H2 in the feeds, respectively. Inspired by the EPOC effect, a composite electrode containing Pd/C and Pt/C catalysts on different sides of a carbon paper was constructed for catalyzing the CO2 reduction without adding H2 to the feeds. Water electrolysis over Pt NPs generates H2, which then effectively promotes formate production over Pd NPs.