“…The sextet peaks (denoted as #) indexed to carbon radicals can be detected only when formic acid and applied potential coexist, confirming the successful activation and reduction of formic acid and implying the generation of *CHO intermediates catalyzed by ER–Cu . Under reduction conditions (−0.4 V vs RHE), the other peaks are attributed to hydrogen radicals . For nitrite reduction, the signals of m / z 33, 17, and 2 are detected by online DEMS, proving the existence of NH 2 OH, NH 3 , and H 2 (Figure d), respectively.…”