11月12日,武漢理工大學(xué)吳勁松/木士春教授在Advanced Science上發(fā)表重要文章,論文題為“
Ultra-Fast and In-Depth Reconstruction of Transition Metal Fluorides in Electrocatalytic Hydrogen Evolution Processes”。迄今為止,幾乎沒(méi)有關(guān)于析氫反應(yīng)(HER)完全重建的報(bào)道。在此,作者開(kāi)發(fā)了一種新型的可重構(gòu)氟化物(如 CoF2)預(yù)催化劑,具有超快速和深度的自重構(gòu),極大地促進(jìn)了 HER 活性。通過(guò)實(shí)驗(yàn)和密度泛函理論 (DFT) 計(jì)算,氟化物、堿性電解質(zhì)和偏置電壓的獨(dú)特表面結(jié)構(gòu)被確定為 HER 過(guò)程中完全重建的關(guān)鍵因素。F原子在氟化物表面的富集提供了自發(fā)和連續(xù)重建的可行性。堿性電解質(zhì)引發(fā)快速 F-浸出并立即補(bǔ)充 OH-以形成無(wú)定形 α-Co(OH)2,該無(wú)定形 α-Co(OH)2 迅速轉(zhuǎn)化為 β-Co(OH)2。偏置電壓促進(jìn)非晶結(jié)晶并加速重建過(guò)程。這些賦予單組分和結(jié)晶 β-Co(OH)2 的生成具有松散和有缺陷的結(jié)構(gòu),導(dǎo)致在 10 mA cm-2下具有 54 mV 的超低過(guò)電位和超過(guò) Pt 的超長(zhǎng)期穩(wěn)定性/C。此外,DFT 計(jì)算證實(shí) F-浸出優(yōu)化了氫和水的吸附能,提高了 HER 動(dòng)力學(xué)。令人印象深刻的是,自重構(gòu)也適用于其他非貴重過(guò)渡金屬氟化物。這項(xiàng)工作建立了對(duì) HER 期間完全自我重建的基本理解,并為構(gòu)思先進(jìn)的催化劑提供了新的視角。
Figure 1. A) Synthetic scheme of hexagram star CoF2 supported on CC. B) FESEM image of CoF1.3(OH)0.7. C) FESEM, D) TEM, E) HAADF-STEM (inset, EELS spectra integrated from red box region), F) HRTEM, and G) HAADF-STEM (inset, SAED pattern) images of CoF2. H–J) Corresponding EDS elemental mappings. Scale bar: (B, C) 2 μm; (D) 500 nm; (E) 20 nm; (F) 5 nm; (G–J) 200 nm, 5 nm?1 (inset).
Figure 2. A) Consecutive LSV curves, B) corresponding overpotentials (@10, 400 mA cm?2), C) consecutive EIS plots, and D) i-t curve of CoF2. E) LSV curves and F) Tafel slopes of R-CoF2, R-NiF2, and R-FeF3 (H2O)0.33 in comparison with commercial Pt/C. G) LSV curves of R-CoF2 and Pt/C before and after successive 3000 cycles CV acceleration. H) i-t curves of R-CoF2 and Pt/C.
Figure 3. A) In situ Raman spectra of CoF2 measured during HER. B) XRD patterns of CoF2 at point A–C in the i-t curve. C) Co 2p, D) O 1s, and E) F 1s spectra of CoF2 at point A–C in i-t curve and initial CoF2.
Figure 4. A) HAADF-STEM image of initial CoF2. B–D) HAADF-STEM images of CoF2 at point A–C (inset, SAED pattern). E) FESEM, F) TEM, G) HRTEM (inset, local FFT-filtered HRTEM image, FFT pattern), and H) atomic-resolution HAADF-STEM (inset, FFT pattern) images of CoF2 at point C. I–L) HAADF-STEM image and corresponding EDS elemental mappings of CoF2 at point C. Scale bar: (A) 50 nm; (B–D) 10 nm, 2 nm?1 (inset); (E) 200 nm; (F) 10 nm; (G) 5 nm, 2 nm?1 (inset); (H) 1 nm, 5 nm?1 (inset); (I–L) 50 nm.
Figure 5. A–D) Optimized structure models, E) Calculated free energy diagram (inset, optimized H* adsorption structure models), and F) H2O adsorption energy diagram (inset, optimized H2O adsorption structure models) of CoF2, CoF2–xOHx, CoF2–y(OH)y, and β-Co(OH)2.
【總結(jié)】
總之,作者構(gòu)建了一類(lèi)新的過(guò)渡金屬氟化物預(yù)催化劑,能夠?qū)崿F(xiàn)超快速和完全自重建,顯著提高堿性介質(zhì)中的 HER 活性。它只需要 54 mV 的超低過(guò)電位即可提供接近商業(yè) Pt/C 催化劑的 10 mA cm-2電流密度,并且 110 小時(shí)的長(zhǎng)期穩(wěn)定性優(yōu)于 Pt/C。實(shí)驗(yàn)結(jié)果和理論計(jì)算共同證實(shí)了氟化物在獨(dú)特的表面結(jié)構(gòu)、堿性電解質(zhì)和偏壓三個(gè)重要條件下的動(dòng)態(tài)重建過(guò)程的發(fā)生。所有這些不僅加速了連續(xù)和更深重建的傳質(zhì),而且還促進(jìn)了堿性 HER 的動(dòng)力學(xué)過(guò)程。具有納米級(jí)結(jié)構(gòu)的重構(gòu)衍生的單組分氫氧化物結(jié)晶相是 HER 性能大大提高的原因。這項(xiàng)工作為 HER 過(guò)程中預(yù)催化劑的重建提供了非常重要的見(jiàn)解,并開(kāi)辟了設(shè)計(jì)高效催化劑的新策略。