Energy consumption and long-term stability of a cathode are two important aspects of great concern in electrocatalytic nitrate reduction. This work studied a binderless FeNi/graphitized mesoporous carbon directly formed on Ni Foam (FeNi/g-mesoC/NF, 7.3 wt % of Fe) and evaluated its electrocatalytic nitrate reduction performance. We proposed a unique structure model of FeNi/g-mesoC/NF cathode in which FeNi alloy nanoparticles were uniformly embedded in mesoporous carbon and graphitized carbon shells were coated on isolated alloy nanoparticles. Oxygen vacancies (OVs) in FeNi oxide passivating layer facilitate the conversion of NO 3 − -N anions on cathode. Toxic NO 2 − -N was almost undetected due to the synergetic effects of FeNi electrocatalysis, and the NO 3 − -N conversion was high in comparation with ever reported iron-based cathode. The NO 3 − -N conversion showed ultrahigh electrocatalytic stability during one-month-recycling test while the physiochemical properties showed negligible change for FeNi/g-mesoC/NF except the increase of OVs. The energy consumption to treat simulated underground water (50% of NO 3 − -N conversion) was low (0.7 kWh mol −1 ) for 50 mg L −1 NO 3 − -N. This binderless composite cathode shows great potential in electrocatalytic NO 3 − -N removal in underground water.

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The high reactivity of Fe(0) with Cr(VI) makes it the best choice for Cr(VI) removal. Interstitial compound Fe 3 C was produced during the carbothermic reduction of mesoporous phenolic resin/ferric ions to form Fe(0)/Fe 3 C nanoparticles embedded in mesoporous carbon (Fe(0)/Fe 3 C@ MesoC). Fe 3 C accelerates the electrochemical corrosion process of α-Fe(0) in solution, and the positive/negative equipotential interface that is formed by iron−carbon (Fe−C) microelectrolysis of Fe(0)/Fe 3 C@MesoC induces the capture of Cr(VI) anions and Cr(III) cations as a result of this process. Cr(VI) was completely reduced to Cr(III) by the Fe(0)/Fe 3 C@MesoC catalyst with a high electron efficiency (40.5%) relative to nanosized zero-valent iron (1.9%) and Fe@MesoC (32.7%). Surface ferrous ions are the principal reactive species responsible for Cr(VI) reduction (at least 64%); Fe(0)/Fe 3 C and undetectable surface ferrous ions account for a small part of Cr(VI) reduction (around 28%), and only 8% of Cr(VI) ions are reduced by active hydrogen (H*). The proposed structure of Fe(0)/Fe 3 C@MesoC provides new insight into iron−carbon material preparation and application in in situ chemical reduction.